Editing Permian–Triassic extinction event (section)

== Hypotheses about cause ==

Explaining an event from 250 million years ago is inherently difficult, with much of the evidence on land eroded or deeply buried, while the [[seafloor spreading|spreading seafloor]] is completely recycled over 200&nbsp;million years, leaving no useful indications beneath the ocean.

Yet, scientists have gathered significant evidence for causes, and several mechanisms have been proposed. The proposals include both catastrophic and gradual processes (similar to those theorized for the [[Cretaceous–Paleogene extinction event]], but with much less current consensus).
*The ''catastrophic'' group includes one or more large [[bolide]] [[impact event]]s, increased [[volcanoes|volcanism]], and sudden release of methane from the seafloor, either due to dissociation of [[methane hydrate]] deposits or metabolism of organic carbon deposits by [[methanogen]]ic microbes.
*The ''gradual'' group includes sea level change, increasing [[Hypoxia (environmental)|hypoxia]], and increasing [[arid]]ity.

Any hypothesis about the cause must explain the selectivity of the event, which affected organisms with calcium carbonate skeletons most severely; the long period (4 to 6&nbsp;million years) before recovery started, and the minimal extent of biological mineralization (despite [[Inorganic compound|inorganic]] carbonates being deposited) once the recovery began.<ref name=Knoll2004 />

=== Volcanism ===
====Siberian Traps====
The flood basalt eruptions that produced the [[large igneous province]] of the [[Siberian Traps]] were among the largest known volcanic events, extruding lava over {{convert|2000000|km2|sqmi}}, roughly the size of Saudi Arabia, producing a catastrophic impact.<ref>{{cite web|author1=Andy Saunders |author2=Marc Reichow |year=2009|title=The Siberian Traps – area and volume |url=http://www.le.ac.uk/gl/ads/SiberianTraps/AreaVolume.html|access-date=2009-10-18}}</ref><ref>{{cite web|year=2023|title=Largest Countries in the World (by area)|url=https://www.worldometers.info/geography/largest-countries-in-the-world/|access-date=2023-05-25}}</ref><ref>{{cite journal |title = The Siberian Traps and the End-Permian mass extinction: a critical review |journal = [[Chinese Science Bulletin]]|volume = 54 |issue = 1 |pages = 20–37 |date = January 2009 |url = http://www.le.ac.uk/gl/ads/SiberianTraps/PDF%20Files/The%20Siberian%20Traps%20and%20the%20End-Permian%20mass.pdf |author1=Saunders, Andy |author2=Reichow, Marc |name-list-style=amp |doi =10.1007/s11434-008-0543-7 |bibcode=2009ChSBu..54...20S |hdl = 2381/27540 |s2cid = 1736350 |hdl-access = free }}</ref><ref>{{cite journal |last1=Reichow |first1=Marc K. |last2=Pringle |first2=M.S. |last3=Al'Mukhamedov |first3=A.I. |last4=Allen |first4=M.B. |last5=Andreichev |first5=V.L. |last6=Buslov |first6=M.M. |last7=Davies |first7=C.E. |last8=Fedoseev |first8=G.S. |last9=Fitton |first9=J.G. |last10=Inger |first10=S. |last11=Medvedev |first11=A.Ya. |last12=Mitchell |first12=C. |last13=Puchkov |first13=V.N. |last14=Safonova |first14=I.Yu. |last15=Scott |first15=R.A. |last16=Saunders |first16=A.D. |display-authors=6 |year=2009 |title= The timing and extent of the eruption of the Siberian Traps large igneous province: Implications for the end-Permian environmental crisis|journal= [[Earth and Planetary Science Letters]] |volume= 277 |issue= 1–2|pages= 9–20 |url= http://www.le.ac.uk/gl/ads/SiberianTraps/PDF%20Files/Reichow%20et%20al.%202009.pdf |doi =10.1016/j.epsl.2008.09.030 |bibcode=2009E&PSL.277....9R|hdl=2381/4204|hdl-access=free}}</ref><ref>{{cite journal |last1=Augland |first1=L. E. |last2=Ryabov |first2=V. V. |last3=Vernikovsky |first3=V. A. |last4=Planke |first4=S. |last5=Polozov |first5=A. G. |last6=Callegaro |first6=S. |last7=Jerram |first7=D. A. |last8=Svensen |first8=H. H. |date=10 December 2019 |title=The main pulse of the Siberian Traps expanded in size and composition |journal=[[Scientific Reports]] |volume=9 |issue=1 |page=18723 |doi=10.1038/s41598-019-54023-2 |pmid=31822688 |pmc=6904769 |bibcode=2019NatSR...918723A }}</ref> The date of the Siberian Traps eruptions matches well with the extinction event.<ref name="Burgess-2014" /><ref>{{Cite journal |title = Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian–Triassic boundary and mass extinction at 251 Ma|last = Kamo |first = SL |year=2003 |journal=[[Earth and Planetary Science Letters]] |doi = 10.1016/S0012-821X(03)00347-9 |bibcode=2003E&PSL.214...75K |volume=214 |issue = 1–2 |pages=75–91}}</ref><ref>{{Cite journal |last1=Black |first1=Benjamin A. |last2=Weiss |first2=Benjamin P. |last3=Elkins-Tanton |first3=Linda T. |last4=Veselovskiy |first4=Roman V. |last5=Latyshev |first5=Anton |date=30 April 2015 |title=Siberian Traps volcaniclastic rocks and the role of magma-water interactions |journal=[[Geological Society of America Bulletin]] |language=en |volume=127 |issue=9–10 |page=B31108.1 |bibcode=2015GSAB..127.1437B |doi=10.1130/B31108.1 |issn=0016-7606}}</ref><ref name="HighPrecisionGeochronology">{{Cite journal |last1=Burgess |first1=Seth D. |last2=Bowring |first2=Samuel A. |date=1 August 2015 |title=High-precision geochronology confirms voluminous magmatism before, during, and after Earth's most severe extinction |journal=[[Science Advances]] |language=en |volume=1 |issue=7 |page=e1500470 |bibcode=2015SciA....1E0470B |doi=10.1126/sciadv.1500470 |issn=2375-2548 |pmc=4643808 |pmid=26601239}}</ref><ref>{{cite AV media |title=Giant eruptions and giant extinctions |medium=video |last=Fischman |first=Josh |website=Scientific American |url=http://www.scientificamerican.com/article/giant-eruptions-and-giant-extinctions-video/ |access-date=2016-03-11}}</ref> A study of the Norilsk and Maymecha-Kotuy regions of the northern Siberian platform indicates that volcanic activity occurred during a few enormous pulses of magma, as opposed to more regular flows.<ref>{{cite journal |last1=Pavlov |first1=Vladimir E. |last2=Fluteau |first2=Frederic |last3=Latyshev |first3=Anton V. |last4=Fetisova |first4=Anna M. |last5=Elkins-Tanton |first5=Linda T. |last6=Black |first6=Ben A. |last7=Burgess |first7=Seth D. |last8=Veselovskiy |first8=Roman V. |date=17 January 2019 |title=Geomagnetic Secular Variations at the Permian-Triassic Boundary and Pulsed Magmatism During Eruption of the Siberian Traps |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GC007950 |journal=[[Geochemistry, Geophysics, Geosystems]] |volume=20 |issue=2 |pages=773–791 |doi=10.1029/2018GC007950 |bibcode=2019GGG....20..773P |s2cid=134521010 |access-date=20 February 2023}}</ref>

The Siberian Traps caused one of the most rapid rises of atmospheric carbon dioxide levels in the geologic record,<ref name="VolumeRateCO2">{{cite journal |last1=Jiang |first1=Qiang |last2=Jourdan |first2=Fred |last3=Olierook |first3=Hugo K. H. |last4=Merle |first4=Renaud E. |last5=Bourdet |first5=Julien |last6=Fougerouse |first6=Denis |last7=Godel |first7=Belinda |last8=Walker |first8=Alex T. |date=25 July 2022 |title=Volume and rate of volcanic {{CO2}} emissions governed the severity of past environmental crises |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=119 |issue=31 |pages=e2202039119 |doi=10.1073/pnas.2202039119 |doi-access=free |pmid=35878029 |pmc=9351498 |bibcode=2022PNAS..11902039J }}</ref> with the rate of carbon dioxide emissions estimated as five times faster than during the preceding catastrophic [[Capitanian mass extinction event|Capitanian mass extinction]]<ref>{{cite journal |last1=Wang |first1=Wen-qian |last2=Zheng |first2=Feifei |last3=Zhang |first3=Shuang |last4=Cui |first4=Ying |last5=Zheng |first5=Quan-feng |last6=Zhang |first6=Yi-chun |last7=Chang |first7=Dong-xun |last8=Zhang |first8=Hua |last9=Xu |first9=Yi-gang |last10=Shen |first10=Shu-zhong |date=15 January 2023 |title=Ecosystem responses of two Permian biocrises modulated by {{CO2}} emission rates |journal=[[Earth and Planetary Science Letters]] |volume=602 |page=117940 |doi=10.1016/j.epsl.2022.117940 |bibcode=2023E&PSL.60217940W |s2cid=254660567 |doi-access=free }}</ref> during the eruption of the [[Emeishan Traps]].<ref name="wignalletal">{{cite journal | url=https://www.science.org/doi/10.1126/science.1171956 | doi=10.1126/science.1171956 | title=Volcanism, Mass Extinction, and Carbon Isotope Fluctuations in the Middle Permian of China | year=2009 | last1=Wignall | first1=Paul Barry | last2=Sun | first2=Yadong | last3=Bond | first3=David P. G. | last4=Izon | first4=Gareth | last5=Newton | first5=Robert J. | last6=Védrine | first6=Stéphanie | last7=Widdowson | first7=Mike | last8=Ali | first8=Jason R. | last9=Lai | first9=Xulong | last10=Jiang | first10=Haishui | last11=Cope | first11=Helen | last12=Bottrell | first12=Simon H. | journal=[[Science (journal)|Science]] | volume=324 | issue=5931 | pages=1179–1182 | pmid=19478179 | bibcode=2009Sci...324.1179W | s2cid=206519019 |access-date=20 February 2023| url-access=subscription }}</ref><ref name="JerramEtAl2016PPP">{{cite journal |last1=Jerram |first1=Dougal A. |last2=Widdowson |first2=Mike |last3=Wignall |first3=Paul Barry |last4=Sun |first4=Yadong |last5=Lai |first5=Xulong |last6=Bond |first6=David P. G. |last7=Torsvik |first7=Trond H. |date=1 January 2016 |title=Submarine palaeoenvironments during Emeishan flood basalt volcanism, SW China: Implications for plume–lithosphere interaction during the Capitanian, Middle Permian ('end Guadalupian') extinction event |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018215003065 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=441 |pages=65–73 |doi=10.1016/j.palaeo.2015.06.009 |bibcode=2016PPP...441...65J |access-date=19 December 2022}}</ref><ref>{{cite journal |last1=Zhou |first1=Mei-Fu |last2=Malpas |first2=John |last3=Song |first3=Xie-Yan |last4=Robinson |first4=Paul T. |last5=Sun |first5=Min |last6=Kennedy |first6=Allen K. |last7=Lesher |first7=C. Michael |last8=Keays |first8=Ride R. |date=15 March 2002 |title=A temporal link between the Emeishan large igneous province (SW China) and the end-Guadalupian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X01006082 |journal=[[Earth and Planetary Science Letters]] |volume=196 |issue=3–4 |pages=113–122 |doi=10.1016/S0012-821X(01)00608-2 |bibcode=2002E&PSL.196..113Z |access-date=20 February 2023|url-access=subscription }}</ref> Overwhelming inorganic [[carbon sink]]s, carbon dioxide levels might have jumped from between 500 and 4,000 ppm prior to the extinction to around 8,000 ppm after, according to one estimate.<ref name="GlobalWarmingAndEPME">{{cite journal |last1=Cui |first1=Ying |last2=Kump |first2=Lee R. |title=Global warming and the end-Permian extinction event: Proxy and modeling perspectives |journal=[[Earth-Science Reviews]] |date=October 2015 |volume=149 |pages=5–22 |doi=10.1016/j.earscirev.2014.04.007 |doi-access=free |bibcode=2015ESRv..149....5C}}</ref> Another study estimated pre-extinction carbon dioxide levels at 400 ppm, which then rose to 2,500 ppm, with 3,900 to 12,000 gigatonnes of carbon added to the ocean-atmosphere system.<ref name="WuEtAl2021NatureCommunications" /> [[Greenhouse effect|Extreme temperature rise]] would have followed,<ref name="White" /> though some evidence suggests a lag of 12,000 to 128,000 years between the rise in volcanic carbon dioxide emissions and global warming.<ref>{{cite journal |last1=Joachimski |first1=Michael M. |last2=Alekseev |first2=A. S. |last3=Grigoryan |first3=A. |last4=Gatovsky |first4=Yu. A. |date=17 June 2019 |title=Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/132/1-2/427/571663/Siberian-Trap-volcanism-global-warming-and-the?redirectedFrom=fulltext |journal=[[Geological Society of America Bulletin]] |volume=132 |issue=1–2 |pages=427–443 |doi=10.1130/B35108.1 |s2cid=197561486 |access-date=26 May 2023|url-access=subscription }}</ref> Although this discrepancy could be also attributed to a incorrect [[biochronology]].<ref>{{Cite journal |last1=Horacek |first1=Micha |last2=Krystyn |first2=Leopold |last3=Baud |first3=Aymon |date=2021-07-23 |title=Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: New insights from Armenian Permian-Triassic sections: Comment |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/134/3-4/1085/606373/Siberian-Trap-volcanism-global-warming-and-the |journal=GSA Bulletin |volume=134 |issue=3–4 |pages=1085–1086 |doi=10.1130/B36099.1 |issn=0016-7606}}</ref> During the latest Permian before the extinction, global average surface temperatures were about 18.2&nbsp;°C,<ref>{{cite journal |last1=Kenny |first1=Ray |date=16 January 2018 |title=A geochemical view into continental palaeotemperatures of the end-Permian using oxygen and hydrogen isotope composition of secondary silica in chert rubble breccia: Kaibab Formation, Grand Canyon (USA) |journal=Geochemical Transactions |volume=19 |issue=2 |page=2 |doi=10.1186/s12932-017-0047-y |pmid=29340852 |pmc=5770344 |bibcode=2018GeoTr..19....2K |doi-access=free }}</ref> which shot up to as much as 35&nbsp;°C, this hyperthermal condition lasting as long as 500,000 years.<ref name="WuEtAl2021NatureCommunications" /> Air temperatures at Gondwana's high southern latitudes experienced a warming of ~10–14&nbsp;°C.<ref name="PaceMagnitudeNatureTerrestrialClimateChange">{{cite journal |last1=Frank |first1=T. D. |last2=Fielding |first2=Christopher R. |last3=Winguth |first3=A. M. E. |last4=Savatic |first4=K. |last5=Tevyaw |first5=A. |last6=Winguth |first6=C. |last7=McLoughlin |first7=Stephen |last8=Vajda |first8=Vivi |last9=Mays |first9=C. |last10=Nicoll |first10=R. |last11=Bocking |first11=M. |last12=Crowley |first12=J. L. |date=19 May 2021 |title=Pace, magnitude, and nature of terrestrial climate change through the end-Permian extinction in southeastern Gondwana |url=https://pubs.geoscienceworld.org/gsa/geology/article/49/9/1089/598763/Pace-magnitude-and-nature-of-terrestrial-climate |journal=[[Geology (journal)|Geology]] |volume=49 |issue=9 |pages=1089–1095 |doi=10.1130/G48795.1 |bibcode=2021Geo....49.1089F |s2cid=236381390 |access-date=2024-03-26}}</ref> According to oxygen isotope shifts from conodont apatite in South China, low latitude surface water temperatures surged about 8&nbsp;°C.<ref name="ClimateWarming">{{cite journal |last1=Joachimski |first1=Michael M. |last2=Lai |first2=Xulong |last3=Shen |first3=Shuzhong |last4=Jiang |first4=Haishui |last5=Luo |first5=Genming |last6=Chen |first6=Bo |last7=Chen |first7=Jun |last8=Sun |first8=Yadong |date=1 March 2012 |title=Climate warming in the latest Permian and the Permian–Triassic mass extinction |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/40/3/195/130777/Climate-warming-in-the-latest-Permian-and-the?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=40 |issue=3 |pages=195–198 |doi=10.1130/G32707.1 |bibcode=2012Geo....40..195J |access-date=2024-03-26|url-access=subscription }}</ref> In present-day Iran, tropical sea surface temperatures were between 27 and 33&nbsp;°C during the Changhsingian but jumped to over 35&nbsp;°C during the PTME.<ref>{{cite journal |last1=Schobben |first1=Martin |last2=Joachimski |first2=Michael M. |last3=Korn |first3=Dieter |last4=Leda |first4=Lucyna |last5=Korte |first5=Christoph |date=September 2014 |title=Palaeotethys seawater temperature rise and an intensified hydrological cycle following the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X13002694 |journal=[[Gondwana Research]] |volume=26 |issue=2 |pages=675–683 |doi=10.1016/j.gr.2013.07.019 |bibcode=2014GondR..26..675S |access-date=31 May 2023|url-access=subscription }}</ref> The increased mean state temperatures also brought stronger [[El Niño–Southern Oscillation|El Nino]] events, heightening short-term climate variability.<ref name=Sun2024>{{cite journal|author1=Yadong Sun|author2=Alexander Farnsworth|author3=Michael M. Joachimski|author4=Paul Barry Wignall|author5=Leopold Krystyn|author6=David P. G. Bond|author7=Domenico C. G. Ravidà|author8=Paul J. Valdes|date=September 12, 2024|title=Mega El Niño instigated the end-Permian mass extinction|journal=[[Science (journal)|Science]]|volume=385|issue=6714|pages=1189–1195 |doi=10.1126/science.ado2030|pmid=39265011 |bibcode=2024Sci...385.1189S |url=https://hull-repository.worktribe.com/file/4785016/1/Accepted%20manuscript |language=en}}</ref>

These extremely high atmospheric carbon dioxide concentrations persisted over a long period.<ref>{{cite journal |last1=Kump |first1=Lee R. |date=3 September 2018 |title=Prolonged Late Permian–Early Triassic hyperthermal: failure of climate regulation? |journal=[[Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences]] |volume=376 |issue=2130 |pages=1–9 |doi=10.1098/rsta.2017.0078 |pmid=30177562 |pmc=6127386 |bibcode=2018RSPTA.37670078K |s2cid=52152614 }}</ref> The position and alignment of Pangaea at the time made the inorganic carbon cycle very inefficient at burying carbon.<ref>{{cite journal |last1=Zhang |first1=Hongrui |last2=Torsvik |first2=Trond H. |date=15 April 2022 |title=Circum-Tethyan magmatic provinces, shifting continents and Permian climate change |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X22000899 |journal=[[Earth and Planetary Science Letters]] |volume=584 |page=117453 |doi=10.1016/j.epsl.2022.117453 |bibcode=2022E&PSL.58417453Z |s2cid=247298020 |access-date=31 May 2023|url-access=subscription }}</ref> In a 2020 paper, scientists reconstructed the mechanisms that led to the extinction event in a [[Biogeochemical cycle#Important cycles|biogeochemical]] model, showed the consequences of the [[greenhouse effect]] on the marine environment, and concluded that the mass extinction can be traced back to volcanic CO{{sub|2}} emissions.<ref>{{cite news |title=Driver of the largest mass extinction in the history of the Earth identified |website=phys.org |language=en |url=https://phys.org/news/2020-10-driver-largest-mass-extinction-history.html |access-date=8 November 2020}}</ref><ref name="Jurikova2020">{{cite journal |last1=Jurikova |first1=Hana |last2=Gutjahr |first2=Marcus |last3=Wallmann |first3=Klaus |last4=Flögel |first4=Sascha |last5=Liebetrau |first5=Volker |last6=Posenato |first6=Renato |last7=Angiolini |first7=Lucia |last8=Garbelli |first8=Claudio |last9=Brand |first9=Uwe |last10=Wiedenbeck |first10=Michael |last11=Eisenhauer |first11=Anton |display-authors=6 |title=Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations |journal=[[Nature Geoscience]] |date=November 2020 |volume=13 |issue=11 |pages=745–750 |doi=10.1038/s41561-020-00646-4 |bibcode=2020NatGe..13..745J |s2cid=224783993 |url=https://www.nature.com/articles/s41561-020-00646-4 |access-date=8 November 2020 |language=en |issn=1752-0908|hdl=11573/1707839 |hdl-access=free }}</ref> Evidence also points to volcanic combustion of underground fossil fuel deposits, based on paired [[Coronene#Occurrence and synthesis|coronene]]-mercury spikes<ref>{{cite news |title=Large volcanic eruption caused the largest mass extinction |website=phys.org |language=en |url=https://phys.org/news/2020-11-large-volcanic-eruption-largest-mass.html |access-date=8 December 2020}}</ref><ref name="KaihoAftabuzzamanJonesTian2020PulsedVolcano">{{cite journal |last1=Kaiho |first1=Kunio |last2=Aftabuzzaman |first2=Md |last3=Jones |first3=David S. |last4=Tian |first4=Li |title=Pulsed volcanic combustion events coincident with the end-Permian terrestrial disturbance and the following global crisis |journal=[[Geology (journal)|Geology]] |date=4 November 2020 |volume=49 |issue=3 |pages=289–293 |doi=10.1130/G48022.1 |issn=0091-7613 |doi-access=free |language=en }} [[File:CC-BY icon.svg|50px]] Available under [https://creativecommons.org/licenses/by/4.0/ CC BY 4.0].</ref> coinciding with geographically widespread mercury anomalies and the rise in isotopically light carbon.<ref>{{cite journal |last1=Shen |first1=Jun |last2=Yu |first2=Jianxin |last3=Chen |first3=Jiubin |last4=Algeo |first4=Thomas J. |last5=Xu |first5=Guozhen |last6=Feng |first6=Qinglai |last7=Shi |first7=Xiao |last8=Planavsky |first8=Noah J. |last9=Shu |first9=Wenchao |last10=Xie |first10=Shucheng |date=25 September 2019 |title=Mercury evidence of intense volcanic effects on land during the Permian-Triassic transition |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/47/12/1117/573755/Mercury-evidence-of-intense-volcanic-effects-on?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=47 |issue=12 |pages=1117–1121 |doi=10.1130/G46679.1 |bibcode=2019Geo....47.1117S |s2cid=204262451 |access-date=26 May 2023|url-access=subscription }}</ref> Te/Th values increase twentyfold over the PTME, further indicating it was concomitant with extreme volcanism.<ref>{{Cite journal |last1=Regelous |first1=Marcel |last2=Regelous |first2=Anette |last3=Grasby |first3=Stephen E. |last4=Bond |first4=David P. G. |last5=Haase |first5=Karsten M. |last6=Gleißner |first6=Stefan |last7=Wignall |first7=Paul Barry |date=31 October 2020 |title=Tellurium in Late Permian-Early Triassic Sediments as a Proxy for Siberian Flood Basalt Volcanism |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GC009064 |journal=[[Geochemistry, Geophysics, Geosystems]] |language=en |volume=21 |issue=11 |doi=10.1029/2020GC009064 |bibcode=2020GGG....2109064R |issn=1525-2027 |access-date=13 March 2024}}</ref> A major volcanogenic influx of isotopically light zinc from the Siberian Traps has also been recorded, further confirming that volcanism was contemporary with the PTME.<ref>{{cite journal |last1=Liu |first1=Sheng-Ao |last2=Wu |first2=Huaichun |last3=Shen |first3=Shu-zhong |last4=Jiang |first4=Ganqing |last5=Zhang |first5=Shihong |last6=Lv |first6=Yiwen |last7=Zhang |first7=Hua |last8=Li |first8=Shuguang |date=1 April 2017 |title=Zinc isotope evidence for intensive magmatism immediately before the end-Permian mass extinction |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/45/4/343/195425/Zinc-isotope-evidence-for-intensive-magmatism?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=45 |issue=4 |pages=343–346 |bibcode=2017Geo....45..343L |doi=10.1130/G38644.1 |access-date=28 March 2023|url-access=subscription }}</ref>

The Siberian Traps eruptions had unusual features that made them even more dangerous. The Siberian lithosphere is rich in [[halogens]] extremely destructive to the ozone layer, and evidence from subcontinental lithospheric xenoliths indicates that as much as 70% of their halogen content was released into the atmosphere.<ref name="BroadleyEtAl2018">{{cite journal |last1=Broadley |first1=Michael W. |last2=Barry |first2=Peter H. |last3=Ballentine |first3=Chris J. |last4=Taylor |first4=Lawrence A. |last5=Burgess |first5=Ray |date=27 August 2018 |title=End-Permian extinction amplified by plume-induced release of recycled lithospheric volatiles |url=https://www.nature.com/articles/s41561-018-0215-4?error=cookies_not_supported&code=eab6ab07-3e24-4b31-a6f9-5b52bbd88177 |journal=[[Nature Geoscience]] |volume=11 |issue=9 |pages=682–687 |doi=10.1038/s41561-018-0215-4 |bibcode=2018NatGe..11..682B |s2cid=133833819 |access-date=28 March 2023}}</ref> Around 18 teratonnes of [[hydrochloric acid]] were emitted,<ref>{{Cite journal |last1=Sobolev |first1=Stephan V. |last2=Sobolev |first2=Alexander V. |last3=Kuzmin |first3=Dmitry V. |last4=Krivolutskaya |first4=Nadezhda A. |last5=Petrunin |first5=Alexey G. |last6=Arndt |first6=Nicholas T. |last7=Radko |first7=Viktor A. |last8=Vasiliev |first8=Yuri R. |date=14 September 2011 |title=Linking mantle plumes, large igneous provinces and environmental catastrophes |url=https://www.nature.com/articles/nature10385 |journal=[[Nature (journal)|Nature]] |language=en |volume=477 |issue=7364 |pages=312–316 |doi=10.1038/nature10385 |pmid=21921914 |bibcode=2011Natur.477..312S |s2cid=205226146 |issn=0028-0836 |access-date=20 September 2023}}</ref> along with sulphur-rich volatiles that caused dust clouds and acid [[aerosols]], which would have blocked out sunlight and disrupted photosynthesis on land and in the [[photic zone]] of the ocean, causing food chains to collapse. These volcanic outbursts of sulphur also induced brief but severe global cooling punctuating the broader trend of rapid global warming,<ref>{{cite journal |last1=Brand |first1=Uwe |last2=Posenato |first2=Renato |last3=Came |first3=Rosemarie |last4=Affek |first4=Hagit |last5=Angiolini |first5=Lucia |last6=Azmy |first6=Karem |last7=Farabegoli |first7=Enzo |date=5 September 2012 |title=The end-Permian mass extinction: A rapid volcanic CO<sub>2</sub> and CH<sub>4</sub>-climatic catastrophe |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254112002938 |journal=[[Chemical Geology]] |volume=322-323 |pages=121–144 |doi=10.1016/j.chemgeo.2012.06.015 |bibcode=2012ChGeo.322..121B |access-date=5 March 2023|url-access=subscription }}</ref> with glacio-eustatic sea level fall.<ref name="BroadleyEtAl2018" /><ref>{{cite journal |last1=Baresel |first1=Björn |last2=Bucher |first2=Hugo |last3=Bagherpour |first3=Borhan |last4=Brosse |first4=Morgane |last5=Guodun |first5=Kuang |last6=Schaltegger |first6=Urs |date=6 March 2017 |title=Timing of global regression and microbial bloom linked with the Permian-Triassic boundary mass extinction: implications for driving mechanisms |journal=[[Scientific Reports]] |volume=7 |page=43630 |doi=10.1038/srep43630 |pmid=28262815 |pmc=5338007 |bibcode=2017NatSR...743630B }}</ref> However, the briefness of these cold events makes them unlikely to have been a significant kill mechanism.<ref>{{Cite journal |last1=Wignall |first1=Paul Barry |last2=Bond |first2=David P. G. |date=25 October 2023 |title=The great catastrophe: causes of the Permo-Triassic marine mass extinction |journal=[[National Science Review]] |language=en |volume=11 |issue=1 |pages=nwad273 |doi=10.1093/nsr/nwad273 |issn=2095-5138 |pmc=10753410 |pmid=38156041 }}</ref>

The eruptions may also have caused acid rain as the aerosols washed out of the atmosphere.<ref>{{cite journal |last1=Maruoka |first1=T. |last2=Koeberl |first2=C. |last3=Hancox |first3=P. J. |last4=Reimold |first4=W. U. |date=30 January 2003 |title=Sulfur geochemistry across a terrestrial Permian–Triassic boundary section in the Karoo Basin, South Africa |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X02010877 |journal=[[Earth and Planetary Science Letters]] |volume=206 |issue=1–2 |pages=101–117 |doi=10.1016/S0012-821X(02)01087-7 |bibcode=2003E&PSL.206..101M |access-date=31 May 2023|url-access=subscription }}</ref> That may have killed land plants and [[mollusk]]s and [[plankton]]ic organisms with calcium carbonate shells. Pure flood basalts produce fluid, low-viscosity lava, and do not hurl debris into the atmosphere. It appears, however, that 20% of the output of the Siberian Traps eruptions was [[Pyroclastic rock|pyroclastic]] ash thrown high into the atmosphere, increasing the short-term cooling effect.<ref>{{cite web |title=Volcanism |website=hoopermuseum.earthsci.carleton.ca |department=Hooper Museum |publisher=Carleton University |place=Ottawa, Ontario, Canada |url=http://hoopermuseum.earthsci.carleton.ca/pt_boundary/Causes/volcanics.html}}</ref> When this had washed out of the atmosphere, the excess carbon dioxide would have remained and global warming would have proceeded unchecked.<ref name="White">{{cite journal |author = White, R. V. |year = 2002 |title = Earth's biggest 'whodunnit': Unravelling the clues in the case of the end-Permian mass extinction |journal = [[Philosophical Transactions of the Royal Society of London]] |volume = 360 |issue = 1801 |pages = 2963–2985 |doi = 10.1098/rsta.2002.1097 |pmid = 12626276 |bibcode = 2002RSPTA.360.2963W |s2cid = 18078072 |url = http://www.le.ac.uk/gl/ads/SiberianTraps/Documents/White2002-P-Tr-whodunit.pdf |access-date = 2008-01-12 |archive-date = 2020-11-11 |archive-url = https://web.archive.org/web/20201111204457/https://www.le.ac.uk/gl/ads/SiberianTraps/Documents/White2002-P-Tr-whodunit.pdf |url-status = dead }}</ref>

Burning of hydrocarbon deposits may have exacerbated the extinction. The Siberian Traps are underlain by thick sequences of Early-Mid [[Paleozoic]] aged [[Carbonate rock|carbonate]] and [[evaporite]] deposits, as well as Carboniferous-Permian aged coal bearing [[clastic rock]]s. When heated, such as by [[igneous intrusion]]s, these rocks may emit large amounts of greenhouse and toxic gases.<ref>{{cite journal |last1=Elkins-Tanton |first1=L. T. |last2=Grasby |first2=Stephen E. |last3=Black |first3=B. A. |last4=Veselovskiy |first4=R. V. |last5=Ardakani |first5=O. H. |last6=Goodarzi |first6=F. |date=12 June 2020 |title=Field evidence for coal combustion links the 252 Ma Siberian Traps with global carbon disruption |journal=[[Geology (journal)|Geology]] |volume=48 |issue=10 |pages=986–991 |doi=10.1130/G47365.1 |bibcode=2020Geo....48..986E |doi-access=free }}</ref> The unique setting of the Siberian Traps over these deposits is likely the reason for the severity of the extinction.<ref>{{cite journal |last1=Svensen |first1=Henrik |last2=Planke |first2=Sverre |last3=Polozov |first3=Alexander G. |last4=Schmidbauer |first4=Norbert |last5=Corfu |first5=Fernando |last6=Podladchikov |first6=Yuri Y. |last7=Jamtveit |first7=Bjørn |date=30 January 2009 |title=Siberian gas venting and the end-Permian environmental crisis |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X08007292 |journal=[[Earth and Planetary Science Letters]] |volume=297 |issue=3–4 |pages=490–500 |doi=10.1016/j.epsl.2008.11.015 |bibcode=2009E&PSL.277..490S |access-date=13 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Konstantinov |first1=Konstantin M. |last2=Bazhenov |first2=Mikhail L. |last3=Fetisova |first3=Anna M. |last4=Khutorskoy |first4=Mikhail D. |date=May 2014 |title=Paleomagnetism of trap intrusions, East Siberia: Implications to flood basalt emplacement and the Permo–Triassic crisis of biosphere |journal=[[Earth and Planetary Science Letters]] |language=en |volume=394 |pages=242–253 |doi=10.1016/j.epsl.2014.03.029 |bibcode=2014E&PSL.394..242K |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X14001733|url-access=subscription }}</ref><ref>{{Cite journal |last1=Chen |first1=Chengsheng |last2=Qin |first2=Shengfei |last3=Wang |first3=Yunpeng |last4=Holland |first4=Greg |last5=Wynn |first5=Peter |last6=Zhong |first6=Wanxu |last7=Zhou |first7=Zheng |date=12 November 2022 |title=High temperature methane emissions from Large Igneous Provinces as contributors to late Permian mass extinctions |journal=[[Nature Communications]] |language=en |volume=13 |issue=1 |pages=6893 |doi=10.1038/s41467-022-34645-3 |pmid=36371500 |pmc=9653473 |bibcode=2022NatCo..13.6893C |issn=2041-1723 }}</ref> The basalt lava erupted or intruded into [[carbonate]] rocks and sediments in the process of forming large coal beds, which would have emitted large amounts of carbon dioxide, leading to stronger global warming after the dust and [[aerosol]]s settled.<ref name="White" /> The change of the eruptions from flood basalt to sill dominated emplacement, liberating even more trapped hydrocarbon deposits, coincides with the main onset of the extinction<ref name="InitialPulse">{{cite journal |last1=Burgess |first1=S. D. |last2=Muirhead |first2=J. D. |last3=Bowring |first3=S. A. |date=31 July 2017 |title=Initial pulse of Siberian Traps sills as the trigger of the end-Permian mass extinction |journal=[[Nature Communications]] |volume=8 |issue=1 |page=164 |doi=10.1038/s41467-017-00083-9 |pmid=28761160 |pmc=5537227 |bibcode=2017NatCo...8..164B |s2cid=3312150 }}</ref> and is linked to a major negative {{delta|13|C}} excursion.<ref>{{cite journal |last1=Dal Corso |first1=Jacopo |last2=Mills |first2=Benjamin J. W. |last3=Chu |first3=Daoling |last4=Newton |first4=Robert J. |last5=Mather |first5=Tamsin A. |last6=Shu |first6=Wenchao |last7=Wu |first7=Yuyang |last8=Tong |first8=Jinnan |last9=Wignall |first9=Paul Barry |date=11 June 2020 |title=Permo–Triassic boundary carbon and mercury cycling linked to terrestrial ecosystem collapse |journal=[[Nature Communications]] |volume=11 |issue=1 |page=2962 |doi=10.1038/s41467-020-16725-4 |pmid=32528009 |pmc=7289894 |bibcode=2020NatCo..11.2962D }}</ref> The intermediate temperature of the Siberian Traps magmas optimised the extremely voluminous release of CO<sub>2</sub> by way of heating of evaporites and carbonates.<ref>{{Cite journal |last=Kaiho |first=Kunio |date=30 April 2024 |title=Role of volcanism and impact heating in mass extinction climate shifts |journal=[[Scientific Reports]] |language=en |volume=14 |issue=1 |pages=9946 |doi=10.1038/s41598-024-60467-y |pmid=38688982 |issn=2045-2322 |pmc=11061309 |bibcode=2024NatSR..14.9946K }}</ref>

Venting of coal-derived methane was accompanied by explosive combustion of coal and discharge of coal-fly ash.<ref name="lava/coal fires" /> A 2011 study led by Stephen E. Grasby reported evidence that volcanism caused massive coal beds to ignite, possibly releasing more than 3&nbsp;trillion tons of carbon. They found ash deposits in deep rock layers near what is now the [[Buchanan Lake Formation]]: "coal ash dispersed by the explosive Siberian Trap eruption would be expected to have an associated release of toxic elements in impacted water bodies where [[fly ash]] slurries developed. ... Mafic megascale eruptions are long-lived events that would allow significant build-up of global ash clouds."<ref>{{cite news |author=Verango, Dan |date=24 January 2011 |title=Ancient mass extinction tied to torched coal |newspaper=[[USA Today]] |url=http://content.usatoday.com/communities/sciencefair/post/2011/01/ancient-mass-extinction-tied-to-torched-coal-/1}}</ref><ref>{{cite journal |author1=Grasby, Stephen E. |author2=Sanei, Hamed |author3=Beauchamp, Benoit |name-list-style=amp |date=January 23, 2011 |title=Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction |journal=[[Nature Geoscience]] |doi=10.1038/ngeo1069 |volume=4|issue=2|pages=104–107|bibcode = 2011NatGe...4..104G }}</ref> Grasby said, "In addition to these volcanoes causing fires through coal, the ash it spewed was highly toxic and was released in the land and water, potentially contributing to the worst extinction event in Earth history."<ref>{{cite press release |title=Researchers find smoking gun of world's biggest extinction: Massive volcanic eruption, burning coal and accelerated greenhouse gas choked out life |date=January 23, 2011 |publisher=University of Calgary |url=http://www.eurekalert.org/pub_releases/2011-01/uoc-rfs012111.php |access-date=26 January 2011}}</ref> However, some researchers propose that these supposed fly ashes were actually the result of wildfires not related to massive coal combustion by intrusive magmatism.<ref>{{cite journal |last1=Hudspith |first1=Victoria A. |last2=Brimmer |first2=Susan M. |last3=Belcher |first3=Claire M. |date=1 October 2014 |title=Latest Permian chars may derive from wildfires, not coal combustion |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/42/10/879/131412/Latest-Permian-chars-may-derive-from-wildfires-not?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=42 |issue=10 |pages=879–882 |doi=10.1130/G35920.1 |bibcode=2014Geo....42..879H |hdl=10871/20251 |access-date=31 May 2023|hdl-access=free }}</ref> A 2013 study led by Q.Y. Yang reported that the total amounts of important volatiles emitted from the Siberian Traps consisted of 8.5 × {{10^|7}} Tg CO{{sub|2}}, 4.4 × {{10^|6}} Tg CO, 7.0 × {{10^|6}} Tg H{{sub|2}}S, and 6.8 × {{10^|7}} Tg SO{{sub|2}}.<ref>{{cite journal |last = Yang |first = Q.Y. |date = 2013 |title = The chemical compositions and abundances of volatiles in the Siberian large igneous province: Constraints on magmatic CO<sub>2</sub> and SO<sub>2</sub> emissions into the atmosphere |journal = [[Chemical Geology]] |volume=339 |pages=84–91 |bibcode =2013ChGeo.339...84T |doi = 10.1016/j.chemgeo.2012.08.031}}</ref>

The sill-dominated emplacement of the Siberian Traps prolonged their warming effects; whereas extrusive volcanism generates an abundance of subaerial basalts that efficiently sequester carbon dioxide via the [[Carbonate–silicate cycle|silicate weathering]] process, underground sills cannot sequester atmospheric carbon dioxide and mitigate global warming.<ref>{{Cite journal |last1=Jones |first1=Morgan T. |last2=Jerram |first2=Dougal A. |last3=Svensen |first3=Henrik H. |last4=Grove |first4=Clayton |date=1 January 2016 |title=The effects of large igneous provinces on the global carbon and sulphur cycles |url=https://www.sciencedirect.com/science/article/pii/S0031018215003557 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Impact, Volcanism, Global changes and Mass Extinctions |volume=441 |pages=4–21 |bibcode=2016PPP...441....4J |doi=10.1016/j.palaeo.2015.06.042 |issn=0031-0182 |access-date=12 January 2024 |via=Elsevier Science Direct}}</ref> Additionally, enhanced reverse weathering and depletion of siliceous carbon sinks enabled extreme warmth to persist for much longer than expected if the excess carbon dioxide was sequestered by silicate rock.<ref name="EnhancedReverseWeathering" />

The reduction in marine primary productivity diminished emissions of [[Dimethyl sulfate|dimethyl sulphate]] and [[Dimethylsulfoniopropionate|dimethylsulphoniopropionate]], enhancing warming.<ref>{{Cite journal |last1=Winguth |first1=Arne M.E. |last2=Shields |first2=Christine A. |last3=Winguth |first3=Cornelia |date=15 December 2015 |title=Transition into a Hothouse World at the Permian–Triassic boundary—A model study |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018215004927 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=440 |pages=316–327 |doi=10.1016/j.palaeo.2015.09.008 |bibcode=2015PPP...440..316W |access-date=13 October 2024 |via=Elsevier Science Direct}}</ref> Also, the decline in biological silicate deposition resulting from the mass extinction of siliceous organisms acted as a positive feedback loop wherein mass death of marine life exacerbated and prolonged extreme hothouse conditions by depleting yet another siliceous carbon sink.<ref>{{cite journal |last1=Isson |first1=Terry T. |last2=Zhang |first2=Shuang |last3=Lau |first3=Kimberly V. |last4=Rauzi |first4=Sofia |last5=Tosca |first5=Nicholas J. |last6=Penman |first6=Donald E. |last7=Planavsky |first7=Noah J. |date=18 June 2022 |title=Marine siliceous ecosystem decline led to sustained anomalous Early Triassic warmth |journal=[[Nature Communications]] |volume=13 |issue=1 |page=3509 |bibcode=2022NatCo..13.3509I |doi=10.1038/s41467-022-31128-3 |pmc=9206662 |pmid=35717338}}</ref>

Mercury anomalies corresponding to the time of Siberian Traps activity have been found in many geographically disparate sites,<ref>{{Cite journal |last1=Wang |first1=Xiangdong |last2=Cawood |first2=Peter A. |last3=Zhao |first3=He |last4=Zhao |first4=Laishi |last5=Grasby |first5=Stephen E. |last6=Chen |first6=Zhong-Qiang |last7=Wignall |first7=Paul Barry |last8=Lv |first8=Zhengyi |last9=Han |first9=Chen |date=15 August 2018 |title=Mercury anomalies across the end Permian mass extinction in South China from shallow and deep water depositional environments |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X18303273 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=496 |pages=159–167 |doi=10.1016/j.epsl.2018.05.044 |bibcode=2018E&PSL.496..159W |access-date=13 October 2024 |via=Elsevier Science Direct}}</ref><ref>{{cite journal |last1=Shen |first1=Jun |last2=Shen |first2=Jiubin |last3=Yu |first3=Jianxin |last4=Algeo |first4=Thomas J. |last5=Smith |first5=Roger M. H. |last6=Botha |first6=Jennifer |last7=Frank |first7=Tracy D. |last8=Fielding |first8=Christopher R. |last9=Ward |first9=Peter D. |last10=Mather |first10=Tamsin A. |date=3 January 2023 |title=Mercury evidence from southern Pangea terrestrial sections for end-Permian global volcanic effects |journal=[[Nature Communications]] |volume=14 |issue=1 |page=6 |pmid=36596767 |doi=10.1038/s41467-022-35272-8 |pmc=9810726 |bibcode=2023NatCo..14....6S }}</ref><ref>{{Cite journal |last1=Wang |first1=Xiangdong |last2=Cawood |first2=Peter A. |last3=Zhao |first3=He |last4=Zhao |first4=Laishi |last5=Grasby |first5=Stephen E. |last6=Chen |first6=Zhong-Qiang |last7=Zhang |first7=Lei |date=1 May 2019 |title=Global mercury cycle during the end-Permian mass extinction and subsequent Early Triassic recovery |url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X19301232 |journal=[[Earth and Planetary Science Letters]] |language=en |volume=513 |pages=144–155 |doi=10.1016/j.epsl.2019.02.026 |bibcode=2019E&PSL.513..144W |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> indicating that these volcanic eruptions released significant quantities of toxic [[mercury (element)|mercury]] into the atmosphere and ocean, causing even larger terrestrial and marine die-offs.<ref name="GrasbyBeuchampBondWignallTalavera">{{cite journal |last1=Grasby |first1=Stephen E. |last2=Beauchamp |first2=Benoit |last3=Bond |first3=David P. G. |last4=Wignall |first4=Paul Barry |last5=Talavera |first5=Cristina |last6=Galloway |first6=Jennifer M. |last7=Piepjohn |first7=Karsten |last8=Reinhardt |first8=Lutz |last9=Blomeier |first9=Dirk |date=1 September 2015 |title=Progressive environmental deterioration in northwestern Pangea leading to the latest Permian extinction |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/127/9-10/1331/126156/Progressive-environmental-deterioration-in?redirectedFrom=fulltext&casa_token=SBzzNzoBSCYAAAAA:OtsqSN19ia2hYYHI9mHwRXG987jdyDf98sfQPKHSP_fJDlhKAZo8lg67LthiuORkeD1ziDTq |journal=[[Geological Society of America Bulletin]] |volume=127 |issue=9–10 |pages=1331–1347 |doi=10.1130/B31197.1 |bibcode=2015GSAB..127.1331G |access-date=14 January 2023}}</ref><ref>{{cite journal |last1=Grasby |first1=Stephen E. |last2=Beauchamp |first2=Benoit |last3=Bond |first3=David P. G. |last4=Wignall |first4=Paul Barry |last5=Sanei |first5=Hamed |year=2016 |title=Mercury anomalies associated with three extinction events (Capitanian Crisis, Latest Permian Extinction and the Smithian/Spathian Extinction) in NW Pangea |journal=[[Geological Magazine]] |volume=153 |issue=2 |pages=285–297 |doi=10.1017/S0016756815000436 |bibcode=2016GeoM..153..285G |s2cid=85549730 |doi-access=free }}</ref><ref>{{cite journal |last1=Sanei |first1=Hamed |last2=Grasby |first2=Stephen E. |last3=Beauchamp |first3=Benoit |date=1 January 2012 |title=Latest Permian mercury anomalies |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/40/1/63/130712/Latest-Permian-mercury-anomalies?redirectedFrom=fulltext&casa_token=6JfaFOQQFCEAAAAA:e5qnj64oyXQsKIktBioNo_B74H5BbzCLiOiY36lj5WmCFkl90xgKoaIAahEYNOQyuXKzqck5 |journal=[[Geology (journal)|Geology]] |volume=40 |issue=1 |pages=63–66 |doi=10.1130/G32596.1 |bibcode=2012Geo....40...63S |access-date=14 January 2023|url-access=subscription }}</ref> A series of surges raised terrestrial and marine environmental mercury concentrations by orders of magnitude above normal background levels and caused [[mercury poisoning]] over periods of a thousand years each.<ref>{{cite journal |last1=Grasby |first1=Stephen E. |last2=Liu |first2=Xiaojun |last3=Yin |first3=Runsheng |last4=Ernst |first4=Richard E. |last5=Chen |first5=Zhuoheng |date=19 May 2020 |title=Toxic mercury pulses into late Permian terrestrial and marine environments |journal=[[Geology (journal)|Geology]] |volume=48 |issue=8 |pages=830–833 |doi=10.1130/G47295.1 |bibcode=2020Geo....48..830G |s2cid=219495628 |doi-access=free }}</ref><ref>{{Cite journal |last1=Paterson |first1=Niall W. |last2=Rossi |first2=Valentina M. |last3=Schneebeli-Hermann |first3=Elke |date=October 2024 |title=Volcanogenic mercury and plant mutagenesis during the end-Permian mass extinction: Palaeoecological perturbation in northern Pangaea |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X24001862 |journal=[[Gondwana Research]] |language=en |volume=134 |pages=123–143 |doi=10.1016/j.gr.2024.06.018 |bibcode=2024GondR.134..123P |access-date=13 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> [[Mutagenesis]] in surviving plants after the PTME coeval with mercury and copper loading confirms volcanically induced [[heavy metal toxicity]].<ref name="MetalStress">{{cite journal |last1=Chu |first1=Daoliang |last2=Dal Corso |first2=Jacopo |last3=Shu |first3=Wenchao |last4=Song |first4=Haijun |last5=Wignall |first5=Paul Barry |last6=Grasby |first6=Stephen E. |last7=Van de Schootbrugge |first7=Bas |last8=Zong |first8=Keqing |last9=Wu |first9=Yuyang |last10=Tong |first10=Jinnan |date=5 February 2021 |title=Metal-induced stress in survivor plants following the end-Permian collapse of land ecosystems |journal=[[Geology (journal)|Geology]] |volume=49 |issue=6 |pages=657–661 |doi=10.1130/G48333.1 |bibcode=2021Geo....49..657C |s2cid=234074046 |doi-access=free }}</ref> Increased bioproductivity may have sequestered mercury and party mitigated poisoning.<ref>{{cite journal |last1=Grasby |first1=Stephen E. |last2=Sanei |first2=Hamed |last3=Beauchamp |first3=Benoit |last4=Chen |first4=Zhuoheng |date=2 August 2013 |title=Mercury deposition through the Permo–Triassic Biotic Crisis |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254113002283 |journal=[[Chemical Geology]] |volume=351 |pages=209–216 |doi=10.1016/j.chemgeo.2013.05.022 |bibcode=2013ChGeo.351..209G |access-date=31 May 2023|url-access=subscription }}</ref> Immense volumes of [[Nickel (element)|nickel]] aerosols and [[cobalt]] and [[arsenic]] emisions, were also released,<ref>{{cite journal |last1=Le Vaillant |first1=Margaux |last2=Barnes |first2=Stephen J. |last3=Mungall |first3=James E. |last4=Mungall |first4=Emma L. |date=21 February 2017 |title=Role of degassing of the Noril'sk nickel deposits in the Permian–Triassic mass extinction event |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=114 |issue=10 |pages=2485–2490 |doi=10.1073/pnas.1611086114 |pmid=28223492 |pmc=5347598 |bibcode=2017PNAS..114.2485L |doi-access=free }}</ref><ref>{{cite journal |last1=Rampino |first1=Michael R. |last2=Rodriguez |first2=Sedelia |last3=Baransky |first3=Eva |last4=Cai |first4=Yue |date=29 September 2017 |title=Global nickel anomaly links Siberian Traps eruptions and the latest Permian mass extinction |journal=[[Scientific Reports]] |volume=7 |issue=1 |page=12416 |doi=10.1038/s41598-017-12759-9 |pmid=28963524 |pmc=5622041 |bibcode=2017NatSR...712416R }}</ref><ref name="GrasbyBeuchampBondWignallTalavera" /> further contributing to metal poisoning.<ref>{{cite journal |last1=Li |first1=Menghan |last2=Grasby |first2=Stephen E. |last3=Wang |first3=Shui-Jiong |last4=Zhang |first4=Xiaolin |last5=Wasylenki |first5=Laura E. |last6=Xu |first6=Yilun |last7=Sun |first7=Mingzhao |last8=Beauchamp |first8=Benoit |last9=Hu |first9=Dongping |last10=Shen |first10=Yanan |date=1 April 2021 |title=Nickel isotopes link Siberian Traps aerosol particles to the end-Permian mass extinction |journal=[[Nature Communications]] |volume=12 |issue=1 |page=2024 |doi=10.1038/s41467-021-22066-7 |pmid=33795666 |pmc=8016954 |bibcode=2021NatCo..12.2024L }}</ref>

The devastation wrought by the Siberian Traps did not end following the Permian-Triassic boundary. Carbon isotope fluctuations suggest that massive Siberian Traps activity recurred many times during the Early Triassic,<ref>{{cite journal |last1=Clarkson |first1=M. O. |last2=Richoz |first2=Sylvain |last3=Wood |first3=R. A. |last4=Maurer |first4=F. |last5=Krystyn |first5=L. |last6=McGurty |first6=D. J. |last7=Astratti |first7=D. |date=July 2013 |title=A new high-resolution δ13C record for the Early Triassic: Insights from the Arabian Platform |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X12003139 |journal=[[Gondwana Research]] |volume=24 |issue=1 |pages=233–242 |doi=10.1016/j.gr.2012.10.002 |bibcode=2013GondR..24..233C |access-date=26 May 2023|url-access=subscription }}</ref><ref>{{Cite journal |last1=Lehrmann |first1=Daniel J. |last2=Stepchinski |first2=Leanne |last3=Altiner |first3=Demir |last4=Orchard |first4=Michael J. |last5=Montgomery |first5=Paul |last6=Enos |first6=Paul |last7=Ellwood |first7=Brooks B. |last8=Bowring |first8=Samuel A. |last9=Ramezani |first9=Jahandar |last10=Wang |first10=Hongmei |last11=Wei |first11=Jiayong |last12=Yu |first12=Meiyi |last13=Griffiths |first13=James D. |last14=Minzoni |first14=Marcello |last15=Schaal |first15=Ellen K. |last16=Li |first16=Xiaowei |last17=Meyer |first17=Katja M. |last18=Payne |first18=Jonathan L. |date=August 2015 |title=An integrated biostratigraphy (conodonts and foraminifers) and chronostratigraphy (paleomagnetic reversals, magnetic susceptibility, elemental chemistry, carbon isotopes and geochronology) for the Permian–Upper Triassic strata of Guandao section, Nanpanjiang Basin, south China |url=https://linkinghub.elsevier.com/retrieve/pii/S1367912015002394 |journal=[[Journal of Asian Earth Sciences]] |language=en |volume=108 |pages=117–135 |doi=10.1016/j.jseaes.2015.04.030 |bibcode=2015JAESc.108..117L |access-date=18 June 2024 |via=Elsevier Science Direct}}</ref> a finding corroborated by mercury spikes,<ref>{{Cite journal |last1=Shen |first1=Jun |last2=Algeo |first2=Thomas J. |last3=Planavsky |first3=Noah J. |last4=Yu |first4=Jianxin |last5=Feng |first5=Qinglai |last6=Song |first6=Haijun |last7=Song |first7=Huyue |last8=Rowe |first8=Harry |last9=Zhou |first9=Lian |last10=Chen |first10=Jiubin |date=August 2019 |title=Mercury enrichments provide evidence of Early Triassic volcanism following the end-Permian mass extinction |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825218302599 |journal=Earth-Science Reviews |language=en |volume=195 |pages=191–212 |doi=10.1016/j.earscirev.2019.05.010 |bibcode=2019ESRv..195..191S |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> causing further extinction events during the epoch.<ref>{{cite journal |last1=Caravaca |first1=Gwénaël |last2=Thomazo |first2=Christophe |last3=Vennin |first3=Emmanuelle |last4=Olivier |first4=Nicolas |last5=Cocquerez |first5=Théophile |last6=Escarguel |first6=Gilles |last7=Fara |first7=Emmanuel |last8=Jenks |first8=James F. |last9=Bylund |first9=Kevin G. |last10=Stephen |first10=Daniel A. |last11=Brayard |first11=Arnaud |date=July 2017 |title=Early Triassic fluctuations of the global carbon cycle: New evidence from paired carbon isotopes in the western USA basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818117300504 |journal=[[Global and Planetary Change]] |volume=154 |pages=10–22 |doi=10.1016/j.gloplacha.2017.05.005 |bibcode=2017GPC...154...10C |s2cid=135330761 |access-date=13 November 2022}}</ref>

====Choiyoi Silicic Large Igneous Province====
A second flood basalt event that produced the Choiyoi Silicic Large Igneous Province in southwestern Gondwana between around 286 Ma and 247 Ma has also been suggested as a significant additional extinction mechanism.<ref name="JosefinaBodnar" /> At 1,300,000 cubic kilometres in volume<ref>{{cite journal |last1=Nelson |first1=D. A. |last2=Cottle |first2=J. M. |date=29 March 2019 |title=Tracking voluminous Permian volcanism of the Choiyoi Province into central Antarctica |journal=[[Lithosphere (journal)|Lithosphere]] |volume=11 |issue=3 |pages=386–398 |doi=10.1130/L1015.1 |bibcode=2019Lsphe..11..386N |s2cid=135130436 |doi-access=free }}</ref> and 1,680,000 square kilometres in area, this event was 40% the size of the Siberian Traps.<ref name="JosefinaBodnar" /> Specifically, this flood basalt has been implicated in the regional demise of the Gondwanan ''Glossopteris'' flora.<ref>{{Cite journal |last1=Spalletti |first1=Luis A. |last2=Limarino |first2=Carlos O. |date=29 September 2017 |title=The Choiyoi magmatism in south western Gondwana: implications for the end-permian mass extinction - a review |url=http://www.andeangeology.cl/index.php/revista1/article/view/V44n3-a05 |journal=[[Andean Geology]] |volume=44 |issue=3 |pages=328 |doi=10.5027/andgeoV44n3-a05 |issn=0718-7106 |access-date=20 September 2023|doi-access=free |bibcode=2017AndGe..44..328S |hdl=11336/66408 |hdl-access=free }}</ref>

====Indochina–South China subduction-zone volcanic arc====
Mercury anomalies preceding the end-Permian extinction have been discovered in what was then the boundary between the South China craton and the Indochinese plate, a subduction zone with a volcanic arc. Hafnium isotopes from syndepositional magmatic zircons found in ash beds created by this volcanic pulse confirm its origin in subduction-zone volcanism rather than large igneous province activity.<ref name="MercuryFluxesRegionalVolcanismSouthChinaCraton" /> The enrichment of copper samples from these deposits in isotopically light copper provide additional confirmation.<ref>{{cite journal |last1=Zhang |first1=Hua |last2=Zhang |first2=Feifei |last3=Chen |first3=Jiubin |last4=Erwin |first4=Douglas H. |last5=Syverson |first5=Drew D. |last6=Ni |first6=Pei |last7=Rampino |first7=Michael R. |last8=Chi |first8=Zhe |last9=Cai |first9=Yao-Feng |last10=Xiang |first10=Lei |last11=Li |first11=We-Qiang |last12=Liu |first12=Sheng-Ao |last13=Wang |first13=Ru-Cheng |last14=Wang |first14=Xiang-Dong |last15=Feng |first15=Zhuo |last16=Li |first16=Hou-Min |last17=Zhang |first17=Ting |last18=Cai |first18=Mong-Ming |last19=Zheng |first19=Wang |last20=Cui |first20=Ying |last21=Zhu |first21=Xiang-Kun |last22=Hou |first22=Zeng-Qian |last23=Wu |first23=Fu-Yuan |last24=Xu |first24=Yi-Gang |last25=Planavsky |first25=Noah J. |last26=Shen |first26=Shu-zhong |date=17 November 2021 |title=Felsic volcanism as a factor driving the end-Permian mass extinction |journal=[[Science Advances]] |volume=7 |issue=47 |pages=eabh1390 |doi=10.1126/sciadv.abh1390 |pmid=34788084 |pmc=8597993 |bibcode=2021SciA....7.1390Z }}</ref> This volcanism has been speculated to have caused local biotic stress among radiolarians, sponges, and brachiopods over the 60,000 years preceding the end-Permian marine extinction, as well as an ammonoid crisis with decreased morphological complexity and size and increased rate of turnover beginning in the lower ''C. yini'' biozone, around 200,000 years before the extinction.<ref name="MercuryFluxesRegionalVolcanismSouthChinaCraton">{{cite journal |last1=Shen |first1=Jun |last2=Chen |first2=Jiubin |last3=Algeo |first3=Thomas J. |last4=Feng |first4=Qinglai |last5=Yu |first5=Jianxin |last6=Xu |first6=Yi-Gang |last7=Xu |first7=Guozhen |last8=Lei |first8=Yong |last9=Planavsky |first9=Noah J. |last10=Xie |first10=Shucheng |date=10 December 2020 |title=Mercury fluxes record regional volcanism in the South China craton prior to the end-Permian mass extinction |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/49/4/452/593185/Mercury-fluxes-record-regional-volcanism-in-the?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=49 |issue=4 |pages=452–456 |doi=10.1130/G48501.1 |s2cid=230524628 |access-date=28 March 2023|url-access=subscription }}</ref>

=== Methane clathrate gasification ===
{{Main|Clathrate gun hypothesis}}
{{Further|Arctic methane emissions}}[[Methane clathrate]]s, also known as methane hydrates, consist of molecules of methane trapped in the crystal lattice of ice. This methane, produced by [[methanogens|methanogen]] microbes, has a {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C [[isotope analysis|isotope ratio]]}} about 6% below normal ({{delta|13|C}} −6.0%). At the right combination of pressure and temperature, clathrates form near the surface of [[permafrost]] and in large quantities on [[continental shelf|continental shelves]] and nearby seabed at water depths of at least {{convert|300|m|ft|abbr=on}}, buried in sediments up to {{convert|2000|m|ft|abbr=on}} below the sea floor.<ref name="Dickens2001">{{cite journal |author=Dickens, G.R. |year=2001 |title=The potential volume of oceanic methane hydrates with variable external conditions |journal=[[Organic Geochemistry]] |volume=32 |issue=10 |pages=1179–1193 |doi=10.1016/S0146-6380(01)00086-9|bibcode=2001OrGeo..32.1179D }}</ref>

Massive release of methane from these clathrates may have contributed to the PTME, as scientists have found worldwide evidence of a swift decrease of about 1% in the{{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }}in [[Carbonate minerals|carbonate]] rocks from the end-Permian.<ref name="Twitchett" /><ref>
{{cite journal |vauthors=Palfy J, Demeny A, Haas J, Htenyi M, Orchard MJ, Veto I |year=2001 |title=Carbon isotope anomaly at the Triassic–Jurassic boundary from a marine section in Hungary |journal=[[Geology (journal)|Geology]] |volume=29 |issue=11 |pages=1047–1050 |bibcode=2001Geo....29.1047P |doi=10.1130/0091-7613(2001)029<1047:CIAAOG>2.0.CO;2 |issn=0091-7613}}</ref> This is the first, largest, and fastest of a series of excursions (decreases and increases) in the ratio, until it abruptly stabilised in the middle Triassic, followed soon afterwards by the recovery of calcifying shelled sealife.<ref name="Payne2004Local" /> The seabed probably contained [[methane hydrate]] deposits, and the lava caused the deposits to dissociate, releasing vast quantities of methane.<ref>{{cite journal |vauthors=Reichow MK, Saunders AD, White RV, Pringle MS, Al'Muhkhamedov AI, Medvedev AI, Kirda NP |year=2002 |title={{nobr| {{sup|40}}Ar ''⁄'' {{sup|39}}Ar }} dates from the West Siberian Basin: Siberian flood basalt province doubled |url=http://eprints.gla.ac.uk/468/1/Reichow_.pdf |journal=[[Science (journal)|Science]] |volume=296 |issue=5574 |pages=1846–1849 |bibcode=2002Sci...296.1846R |doi=10.1126/science.1071671 |pmid=12052954 |s2cid=28964473}}</ref>
A vast release of methane might cause significant global warming since methane is a very powerful [[Methane#Methane as a greenhouse gas|greenhouse gas]]. Strong evidence suggests the global temperatures increased by about 6&nbsp;°C (10.8&nbsp;°F) near the equator and therefore by more at higher latitudes: a sharp decrease in oxygen isotope ratios ({{nobr|{{sup|18}}O ''⁄'' {{sup|16}}O}});<ref>{{cite journal |vauthors=Holser WT, Schoenlaub HP, Attrep Jr M, Boeckelmann K, Klein P, Magaritz M, Orth CJ, Fenninger A, Jenny C, Kralik M, Mauritsch H, Pak E, Schramm JF, Stattegger K, Schmoeller R |year=1989 |title=A unique geochemical record at the Permian/Triassic boundary |journal=[[Nature (journal)|Nature]] |volume=337 |issue=6202 |pages=39–44 |bibcode=1989Natur.337...39H |doi=10.1038/337039a0 |s2cid=8035040}}</ref> the extinction of ''[[Glossopteris]]'' flora (''Glossopteris'' and plants that grew in the same areas), which needed a cold [[climate]], with its replacement by floras typical of lower paleolatitudes.<ref>{{cite journal |author=Dobruskina, I.A. |year=1987 |title=Phytogeography of Eurasia during the early Triassic |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=58 |issue=1–2 |pages=75–86 |bibcode=1987PPP....58...75D |doi=10.1016/0031-0182(87)90007-1}}</ref> It was also suggested that a large-scale release of methane and other [[greenhouse gas]]es from the ocean into the atmosphere was connected to the [[anoxic event]]s and euxinic (sulfidic) events at the time, with the exact mechanism compared to the 1986 [[Lake Nyos disaster]].<ref name="Ryskin 2003">{{cite journal |last=Ryskin |first=Gregory |date=September 2003 |title=Methane-driven oceanic eruptions and mass extinctions |journal=[[Geology (journal)|Geology]] |volume=31 |issue=9 |pages=741–744 |bibcode=2003Geo....31..741R |doi=10.1130/G19518.1}}</ref>

The clathrate hypothesis seemed the only proposed mechanism sufficient to cause a global 1% reduction in the {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }}.<ref>{{cite journal |last1=Krull |first1=Evelyn S. |last2=Retallack |first2=Gregory J. |date=1 September 2000 |title=<sup>13</sup>C depth profiles from paleosols across the Permian–Triassic boundary: Evidence for methane release |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/112/9/1459/183682/13C-depth-profiles-from-paleosols-across-the?redirectedFrom=fulltext |journal=[[Geological Society of America Bulletin]] |volume=112 |issue=9 |pages=1459–1472 |bibcode=2000GSAB..112.1459K |doi=10.1130/0016-7606(2000)112<1459:CDPFPA>2.0.CO;2 |issn=0016-7606 |access-date=3 July 2023|url-access=subscription }}</ref><ref name="Erwin1993" /> While a variety of factors may have contributed to the ratio drop, a 2002 review found most of them insufficient to account for the observed amount:<ref name="Berner2002" /> 
* Gases from volcanic eruptions have a{{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }}about 0.5 to 0.8% below standard ({{delta|13|C}} −0.5 to −0.8%), but a 1995 assessment concluded that the observed 1.0% worldwide reduction would have required eruptions massively larger than any found.<ref name="Dickens1995">{{cite journal |vauthors=Dickens GR, O'Neil JR, Rea DK, Owen RM |year=1995|title=Dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the Paleocene |journal=[[Paleoceanography and Paleoclimatology]] |volume=10 |issue=6 |pages=965–971 |doi=10.1029/95PA02087 |bibcode=1995PalOc..10..965D}}</ref> (However, this analysis addressed only CO<sub>2</sub> produced by the magma itself, not from interactions with carbon bearing sediments, as described below.)
* A reduction in organic activity would extract {{sup|12}}C more slowly from the environment and leave more of it to be incorporated into sediments, thus reducing the{{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio. }} [[Biochemistry|Biochemical]] processes preferentially use the lighter isotopes since chemical reactions are ultimately driven by electromagnetic forces between atoms and lighter isotopes respond more quickly to these forces, but a study of a smaller drop of 0.3 to 0.4% in {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C }} ({{delta|13|C}} −3 to −4&nbsp;‰) at the [[Paleocene-Eocene Thermal Maximum]] (PETM) concluded that even transferring all the organic [[carbon]] (in organisms, soils, and dissolved in the ocean) into sediments would be insufficient: Even such a large burial of material rich in {{sup|12}}C would not have produced the 'smaller' drop in the {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} of the rocks around the PETM.<ref name="Dickens1995" />
* Buried sedimentary organic matter has a {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} 2.0 to 2.5% below normal ({{delta|13|C}} −2.0 to −2.5%). Theoretically, if the sea level fell sharply, shallow [[marine sediment]]s would be exposed to oxidation. But 6,500–8,400 gigatonnes (1 gigatonne = {{10^|12}} kg) of organic carbon would have to be oxidized and returned to the ocean-atmosphere system within less than a few hundred thousand years to reduce the {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} by 1.0%, which is not thought to be a realistic possibility.<ref name="Erwin1993" /> Moreover, sea levels were rising rather than falling at the time of the extinction.<ref name="White" />
* Rather than a sudden decline in sea level, intermittent periods of ocean-bottom [[hyperoxia]] and [[Anoxic sea water|anoxia]] (high-oxygen and low- or zero-oxygen conditions) may have caused the {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} fluctuations in the Early Triassic;<ref name="Payne2004Local" /> and global anoxia may have been responsible for the end-Permian blip. The continents of the end-Permian and early Triassic were more clustered in the tropics than they are now, and large tropical rivers would have dumped sediment into smaller, partially enclosed ocean basins at low latitudes. Such conditions favor oxic and anoxic episodes; oxic/anoxic conditions would result in a rapid release/burial, respectively, of large amounts of organic carbon, which has a low {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} because biochemical processes use the lighter isotopes more.<ref name="SchragBernerEtAl2002">{{cite journal |vauthors=Schrag DP, Berner RA, Hoffman PF, Halverson GP |year=2002 |title=On the initiation of a snowball Earth |journal=[[Geochemistry, Geophysics, Geosystems]] |volume=3 |issue=6 |pages=1–21 |doi=10.1029/2001GC000219 |bibcode=2002GGG.....3.1036S |doi-access=free }}
Preliminary abstract at {{cite web | author=Schrag, D.P. | date=June 2001 | title=On the initiation of a snowball Earth | publisher=Geological Society of America | url=http://gsa.confex.com/gsa/2001ESP/finalprogram/abstract_8038.htm | access-date=2008-04-20 | url-status=dead | archive-url=https://web.archive.org/web/20180425115243/https://gsa.confex.com/gsa/2001ESP/finalprogram/abstract_8038.htm | archive-date=2018-04-25 }}</ref> That or another organic-based reason may have been responsible for both that and a late Proterozoic/Cambrian pattern of fluctuating {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratios.}}<ref name="Payne2004Local" />

However, the clathrate hypothesis has also been criticized. Carbon-cycle models that include consideration of roasting carbonate sediments by volcanism confirm that it would have had enough effect to produce the observed reduction.<ref name="Berner2002">
{{cite journal| author = Berner, R.A.| year = 2002| title = Examination of hypotheses for the Permo-Triassic boundary extinction by carbon cycle modeling |journal = [[Proceedings of the National Academy of Sciences of the United States of America]] |volume=99 |issue=7 |pages=4172–4177 |doi=10.1073/pnas.032095199 |doi-access=free |pmid=11917102 |pmc=123621  |bibcode = 2002PNAS...99.4172B }}</ref><ref name="Benton2003">{{cite journal|author1 = Benton, Michael James  | author1-link = Michael Benton | author2=Twitchett, R.J.| year = 2003 |title=How to kill (almost) all life: The end-Permian extinction event | journal = [[Trends in Ecology & Evolution]] |volume = 18 | issue = 7 | pages = 358–365 |doi = 10.1016/S0169-5347(03)00093-4 }}</ref> Also, the pattern of isotope shifts expected to result from a massive release of methane does not match the patterns seen throughout the Early Triassic. Not only would such a cause require the release of five times as much methane as postulated for the PETM, but would it also have to be reburied at an unrealistically high rate to account for the rapid increases in the {{nobr| {{sup|13}}C ''⁄'' {{sup|12}}C ratio }} (episodes of high positive {{delta|13|C}}) throughout the early Triassic before it was released several times again.<ref name="Payne2004Local" /> The latest research suggests that greenhouse gas release during the extinction event was dominated by volcanic carbon dioxide,<ref>{{cite journal |last1=Cui |first1=Ying |last2=Li |first2=Mingsong |last3=van Soelen |first3=Elsbeth E. |last4=Peterse |first4=Francien |last5=M. Kürschner |first5=Wolfram |date=7 September 2021 |title=Massive and rapid predominantly volcanic {{CO2}} emission during the end-Permian mass extinction |journal= [[Proceedings of the National Academy of Sciences of the United States of America]] |volume=118 |issue=37 |pages=e2014701118 |doi=10.1073/pnas.2014701118 |pmid=34493684 |pmc=8449420 |bibcode=2021PNAS..11814701C |doi-access=free }}</ref> and while methane release had to have contributed, isotopic signatures show that thermogenic methane released from the Siberian Traps had consistently played a larger role than methane from clathrates and any other biogenic sources such as wetlands during the event.<ref name="WuEtAl2021NatureCommunications">{{cite journal |last1=Wu |first1=Yuyang |last2=Chu |first2=Daoliang |last3=Tong |first3=Jinnan |last4=Song |first4=Haijun |last5=Dal Corso |first5=Jacopo |last6=Wignall |first6=Paul Barry |last7=Song |first7=Huyue |last8=Du |first8=Yong |last9=Cui |first9=Ying |date=9 April 2021 |title=Six-fold increase of atmospheric ''p''{{CO2}} during the Permian–Triassic mass extinction |url=https://www.researchgate.net/publication/350759904 |journal=[[Nature Communications]] |volume=12 |issue=1 |page=2137 |doi=10.1038/s41467-021-22298-7 |pmid=33837195 |pmc=8035180 |bibcode=2021NatCo..12.2137W |s2cid=233200774 |access-date=2024-03-26}}</ref>

Adding to the evidence against methane clathrate release as the central driver of warming, the main rapid warming event is also associated with marine transgression rather than regression; the former would not normally have initiated methane release, which would have instead required a decrease in pressure, something that would be generated by a retreat of shallow seas.<ref>{{cite journal |last1=Shen |first1=Shu-Zhong |last2=Cao |first2=Chang-Qun |last3=Henderson |first3=Charles M. |last4=Wang |first4=Xiang-Dong |last5=Shi |first5=Guang R. |last6=Wang |first6=Yue |last7=Wang |first7=Wei |date=January 2006 |title=End-Permian mass extinction pattern in the northern peri-Gondwanan region |url=https://www.sciencedirect.com/science/article/abs/pii/S1871174X06000072 |journal=[[Palaeoworld]] |volume=15 |issue=1 |pages=3–30 |doi=10.1016/j.palwor.2006.03.005 |access-date=26 May 2023|url-access=subscription }}</ref> The configuration of the world's landmasses into one supercontinent would also mean that the global gas hydrate reservoir was lower than today, further damaging the case for methane clathrate dissolution as a major cause of the carbon cycle disruption.<ref>{{Cite journal |last1=Majorowicz |first1=J. |last2=Grasby |first2=S. E. |last3=Safanda |first3=J. |last4=Beauchamp |first4=B. |date=1 May 2014 |title=Gas hydrate contribution to Late Permian global warming |url=https://www.sciencedirect.com/science/article/pii/S0012821X14001460 |journal=[[Earth and Planetary Science Letters]] |volume=393 |pages=243–253 |doi=10.1016/j.epsl.2014.03.003 |bibcode=2014E&PSL.393..243M |issn=0012-821X |access-date=12 January 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref>

=== Hypercapnia and acidification ===
Marine organisms are more sensitive to changes in {{CO2}} (carbon dioxide) levels than terrestrial organisms for a variety of reasons. {{CO2}} is 28 times more [[Solubility|soluble]] in water than oxygen. Marine animals normally function with lower concentrations of {{CO2}} in their bodies than land animals, as the removal of {{CO2}} in air-breathing animals is impeded by the need for the gas to pass through the respiratory system's [[Biological membrane|membrane]]s ([[lung]]s' [[Pulmonary alveolus|alveolus]], [[Invertebrate trachea|tracheae]], and the like), even when {{CO2}} diffuses more easily than oxygen. In marine organisms, relatively modest but sustained increases in {{CO2}} concentrations hamper the synthesis of [[protein]]s, reduce fertilization rates, and produce [[Deformity|deformities]] in calcareous hard parts.<ref name="KNollBambach2007Paleophysiology" /> Higher concentrations of {{CO2}} also result in decreased activity levels in many active marine animals, hindering their ability to obtain food.<ref>{{cite journal |last1=Reddin |first1=Carl J. |last2=Nätscher |first2=Paulina |last3=Kocsis |first3=Ádám T. |last4=Pörtner |first4=Hans-Otto |last5=Kiessling |first5=Wolfgang |date=10 February 2020 |title=Marine clade sensitivities to climate change conform across timescales |url=https://www.nature.com/articles/s41558-020-0690-7?error=cookies_not_supported&code=a63948f1-abe4-434a-8ad5-962232192c04 |journal=[[Nature Climate Change]] |volume=10 |issue=3 |pages=249–253 |doi=10.1038/s41558-020-0690-7 |bibcode=2020NatCC..10..249R |s2cid=211074044 |access-date=26 March 2023|url-access=subscription }}</ref> An analysis of marine fossils from the Permian's final [[Changhsingian]] stage found that marine organisms with a low tolerance for [[hypercapnia]] (high concentration of carbon dioxide) had high extinction rates, and the most tolerant organisms had very slight losses. The most vulnerable marine organisms were those that produced calcareous hard parts (from calcium carbonate) and had low [[metabolic rate]]s and weak [[respiratory system]]s, notably [[calcareous sponge]]s, [[Rugose coral|rugose]] and [[tabulate coral]]s, [[calcite]]-depositing brachiopods, bryozoans, and [[echinoderm]]s; about 81% of such genera became extinct. Close relatives without [[calcareous]] hard parts suffered only minor losses, such as [[sea anemone]]s, from which modern corals evolved. Animals with high metabolic rates, well-developed respiratory systems, and non-calcareous hard parts had negligible losses except for [[conodont]]s, in which 33% of genera died out. This pattern is also consistent with what is known about the effects of [[Hypoxia (environmental)|hypoxia]], a shortage but not total absence of [[oxygen]]. However, hypoxia cannot have been the only killing mechanism for marine organisms. Nearly all of the [[continental shelf]] waters would have had to become severely hypoxic to account for the magnitude of the extinction, but such a catastrophe would make it difficult to explain the very selective pattern of the extinction. [[Mathematical models]] of the Late Permian and Early Triassic atmospheres show a significant but protracted decline in atmospheric oxygen levels, with no acceleration near the P–Tr boundary. Minimum atmospheric oxygen levels in the Early Triassic are never less than present-day levels and so the decline in oxygen levels does not match the temporal pattern of the extinction.<ref name="KNollBambach2007Paleophysiology" />

In addition, an increase in {{CO2}} concentration is inevitably linked to ocean acidification,<ref>{{cite journal |last1=Cui |first1=Ying |last2=Kump |first2=Lee R. |last3=Ridgwell |first3=Andy |date=1 November 2013 |title=Initial assessment of the carbon emission rate and climatic consequences during the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018213003969 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=389 |pages=128–136 |doi=10.1016/j.palaeo.2013.09.001 |bibcode=2013PPP...389..128C |access-date=26 June 2023|url-access=subscription }}</ref> consistent with the preferential extinction of heavily calcified taxa and other signals in the rock record that suggest a more [[acid]]ic ocean,<ref name="CalciumIsotopeConstraints">{{Cite journal |last1=Payne |first1=J. |last2=Turchyn |first2=A. |last3=Paytan |first3=A. |last4=Depaolo |first4=D. |last5=Lehrmann |first5=D. |last6=Yu |first6=M. |last7=Wei |first7=J. |year=2010 |title=Calcium isotope constraints on the end-Permian mass extinction |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=107 |issue=19 |pages=8543–8548 |bibcode=2010PNAS..107.8543P |doi=10.1073/pnas.0914065107 |pmc=2889361 |pmid=20421502 |doi-access=free}}</ref> such as a carbonate production crisis that occurred a few thousand years after volcanic greenhouse gas emissions began.<ref>{{Cite journal |last1=He |first1=Jiawei |last2=Hu |first2=Xiumian |last3=Li |first3=Juan |last4=Kemp |first4=David B. |last5=Hou |first5=Mingcai |last6=Han |first6=Zhong |date=15 November 2024 |title=Millennial-scale sedimentary evolution of carbonate platforms during the Permian–Triassic boundary hyperthermal event |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018224004449 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=654 |pages=112455 |doi=10.1016/j.palaeo.2024.112455 |bibcode=2024PPP...65412455H |access-date=13 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> The decrease in ocean pH is calculated to be up to 0.7 units.<ref name="OceanAcidificaton">{{cite journal |last1=Clarkson |first1=M. |last2=Kasemann |first2=S. |last3=Wood |first3=R. |last4=Lenton |first4=T. |last5=Daines |first5=S. |last6=Richoz |first6=S. |last7=Ohnemueller |first7=F. |last8=Meixner |first8=A. |last9=Poulton |first9=S. |last10=Tipper |first10=E. |display-authors=6 |date=2015-04-10 |title=Ocean acidification and the Permo-Triassic mass extinction |url=http://eprints.whiterose.ac.uk/85124/1/Clarkson_Boron_final.pdf |journal=[[Science (journal)|Science]] |volume=348 |issue=6231 |pages=229–232 |bibcode=2015Sci...348..229C |doi=10.1126/science.aaa0193 |pmid=25859043 |hdl=10871/20741 |s2cid=28891777}}</ref> An extreme [[aragonite sea]] formed.<ref>{{Cite journal |last1=Li |first1=Fei |last2=Yan |first2=Jiaxin |last3=Chen |first3=Zhong-Qiang |last4=Ogg |first4=James G. |last5=Tian |first5=Li |last6=Korngreen |first6=Dorit |last7=Liu |first7=Ke |last8=Ma |first8=Zulu |last9=Woods |first9=Adam D. |date=October 2015 |title=Global oolite deposits across the Permian–Triassic boundary: A synthesis and implications for palaeoceanography immediately after the end-Permian biocrisis |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825214002268 |journal=[[Earth-Science Reviews]] |language=en |volume=149 |pages=163–180 |doi=10.1016/j.earscirev.2014.12.006 |bibcode=2015ESRv..149..163L |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Ocean acidification was most extreme at mid-latitudes, and the major marine transgression associated with the end-Permian extinction is believed to have devastated shallow shelf communities in conjunction with anoxia.<ref name="LysoclineShoaling">{{cite journal |last1=Beauchamp |first1=Benoit |last2=Grasby |first2=Stephen E. |date=15 September 2012 |title=Permian lysocline shoaling and ocean acidification along NW Pangea led to carbonate eradication and chert expansion |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018212003586 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=350-352 |pages=73–90 |doi=10.1016/j.palaeo.2012.06.014 |bibcode=2012PPP...350...73B |access-date=2024-03-26|url-access=subscription }}</ref> Evidence from paralic facies spanning the Permian-Triassic boundary in western [[Guizhou]] and eastern [[Yunnan]], however, shows a local [[marine transgression]] dominated by carbonate deposition, suggesting that ocean acidification did not occur across the entire globe and was likely limited to certain regions of the world's oceans.<ref name="WignallEtAl2020">{{cite journal |last1=Wignall |first1=Paul Barry |last2=Chu |first2=Daoliang |last3=Hilton |first3=Jason M. |last4=Dal Corso |first4=Jacopo |last5=Wu |first5=Yuyang |last6=Wang |first6=Yao |last7=Atkinson |first7=Jed |last8=Tong |first8=Jinnan |date=June 2020 |title=Death in the shallows: The record of Permo-Triassic mass extinction in paralic settings, southwest China |journal=[[Global and Planetary Change]] |volume=189 |page=103176 |doi=10.1016/j.gloplacha.2020.103176 |bibcode=2020GPC...18903176W |s2cid=216302513 |doi-access=free }}</ref> One study, published in ''[[Scientific Reports]]'', concluded that widespread ocean acidification, if it did occur, was not intense enough to impede calcification and only occurred during the beginning of the extinction event.<ref>{{cite journal |last1=Foster |first1=William J. |last2=Hirtz |first2=J. A. |last3=Farrell |first3=C. |last4=Reistroffer |first4=M. |last5=Twitchett |first5=Richard J. |last6=Martindale |first6=R. C. |date=24 January 2022 |title=Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction |journal=[[Scientific Reports]] |volume=12 |issue=1 |page=1202 |doi=10.1038/s41598-022-04991-9 |pmid=35075151 |pmc=8786885 |bibcode=2022NatSR..12.1202F }}</ref> The relative success of many marine organisms that were very vulnerable to acidification has further been used to argue that acidification was not a major extinction contributor.<ref>{{cite book |last1=Wignall |first1=Paul Barry |date=29 September 2015 |title=The Worst of Times: How Life on Earth Survived Eighty Million Years of Extinctions |chapter=The Killing Seas |location=Princeton |publisher=[[Princeton University Press]] |pages=83–84 |isbn=978-0-691-14209-8}}</ref> The persistence of highly elevated carbon dioxide concentrations in the atmosphere and ocean during the Early Triassic would have impeded the recovery of biocalcifying organisms after the PTME.<ref name="ElevatedAtmosphericCO2DelayedBioticRecovery">{{cite journal |last1=Fraiser |first1=Margaret L. |last2=Bottjer |first2=David P. |date=20 August 2007 |title=Elevated atmospheric CO2 and the delayed biotic recovery from the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018207001150 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=252 |issue=1–2 |pages=164–175 |doi=10.1016/j.palaeo.2006.11.041 |bibcode=2007PPP...252..164F |access-date=31 May 2023|url-access=subscription }}</ref>

Acidity generated by increased carbon dioxide concentrations in soil and sulphur dioxide dissolution in rainwater was also a kill mechanism on land.<ref>{{cite journal |last1=Heydari |first1=Ezat |last2=Arzani |first2=Nasser |last3=Hassanzadeh |first3=Jamshin |date=7 July 2008 |title=Mantle plume: The invisible serial killer — Application to the Permian–Triassic boundary mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018208002150 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=264 |issue=1–2 |pages=147–162 |doi=10.1016/j.palaeo.2008.04.013 |bibcode=2008PPP...264..147H |access-date=26 May 2023|url-access=subscription }}</ref> The increasing acidification of rainwater caused increased soil erosion as a result of the increased acidity of forest soils, evidenced by the increased influx of terrestrially derived organic sediments found in marine sedimentary deposits during the end-Permian extinction.<ref>{{cite journal |last1=Sephton |first1=Mark A. |last2=Jiao |first2=Dan |last3=Engel |first3=Michael H. |last4=Looy |first4=Cindy V. |last5=Visscher |first5=Henk |date=1 February 2015 |title=Terrestrial acidification during the end-Permian biosphere crisis? |url=https://pubs.geoscienceworld.org/gsa/geology/article/43/2/159/131802/Terrestrial-acidification-during-the-end-Permian |journal=[[Geology (journal)|Geology]] |volume=43 |issue=2 |pages=159–162 |doi=10.1130/G36227.1 |bibcode=2015Geo....43..159S |access-date=23 December 2022|hdl=10044/1/31566 |hdl-access=free }}</ref> Further evidence of an increase in soil acidity comes from elevated Ba/Sr ratios in earliest Triassic soils.<ref>{{cite journal |last1=Sheldon |first1=Nathan D.  |date=28 February 2006 |title=Abrupt chemical weathering increase across the Permian–Triassic boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018205005213 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=231 |issue=3–4 |pages=315–321 |doi=10.1016/j.palaeo.2005.09.001 |bibcode=2006PPP...231..315S |access-date=24 April 2023|url-access=subscription }}</ref> A positive feedback loop further enhancing and prolonging [[soil acidification]] may have resulted from the decline of infaunal invertebrates like tubificids and chironomids, which remove acid metabolites from the soil.<ref>{{cite journal |last1=Buatois |first1=Luis A. |last2=Borruel-Abadía |first2=Violeta |last3=De la Horra |first3=Raúl |last4=Galán-Abellán |first4=Ana Belén |last5=López-Gómez |first5=José |last6=Barrenechea |first6=José F. |last7=Arche |first7=Alfredo |date=25 March 2021 |title=Impact of Permian mass extinctions on continental invertebrate infauna |url=https://onlinelibrary.wiley.com/doi/full/10.1111/ter.12530 |journal=[[Terra Nova (journal)|Terra Nova]] |volume=33 |issue=5 |pages=455–464 |doi=10.1111/ter.12530 |bibcode=2021TeNov..33..455B |s2cid=233616369 |access-date=23 December 2022|url-access=subscription }}</ref> The increased abundance of vermiculitic clays in Shansi, South China coinciding with the Permian-Triassic boundary strongly suggests a sharp drop in soil pH causally related to volcanogenic emissions of carbon dioxide and sulphur dioxide.<ref>{{cite journal |last1=Xu |first1=Guozhen |last2=Deconinck |first2=Jean-François |last3=Feng |first3=Qinglai |last4=Baudin |first4=François |last5=Pellenard |first5=Pierre |last6=Shen |first6=Jun |last7=Bruneau |first7=Ludovic |date=15 May 2017 |title=Clay mineralogical characteristics at the Permian–Triassic Shangsi section and their paleoenvironmental and/or paleoclimatic significance |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018216302917 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=474 |pages=152–163 |doi=10.1016/j.palaeo.2016.07.036 |bibcode=2017PPP...474..152X |access-date=23 December 2022|url-access=subscription }}</ref> [[Hopane]] anomalies have also been interpreted as evidence of acidic soils and peats.<ref>{{cite journal |last1=Wang |first1=Chunjiang |date=January 2007 |title=Anomalous hopane distributions at the Permian–Triassic boundary, Meishan, China – Evidence for the end-Permian marine ecosystem collapse |url=https://www.sciencedirect.com/science/article/abs/pii/S0146638006002208 |journal=[[Organic Geochemistry]] |volume=38 |issue=1 |pages=52–66 |doi=10.1016/j.orggeochem.2006.08.014 |bibcode=2007OrGeo..38...52W |access-date=23 May 2023|url-access=subscription }}</ref> As with many other environmental stressors, acidity on land episodically persisted well into the Triassic, stunting the recovery of terrestrial ecosystems.<ref>{{cite journal |last1=Borruel-Abadía |first1=Violeta |last2=Barrenechea |first2=José F. |last3=Galán-Abellán |first3=Ana Belén |last4=De la Horra |first4=Raúl |last5=López-Gómez |first5=José |last6=Ronchi |first6=Ausonio |last7=Luque |first7=Francisco Javier |last8=Alonso-Azcárate |first8=Jacinto |last9=Marzo |first9=Mariano |date=20 June 2019 |title=Could acidity be the reason behind the Early Triassic biotic crisis on land? |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254119301597 |journal=[[Chemical Geology]] |volume=515 |pages=77–86 |doi=10.1016/j.chemgeo.2019.03.035 |bibcode=2019ChGeo.515...77B |s2cid=134704729 |access-date=18 December 2022|url-access=subscription }}</ref>

=== Anoxia and euxinia ===
{{See also|Anoxic event}}
Evidence for widespread ocean [[anoxic waters|anoxia]] (severe deficiency of oxygen) and [[euxinia]] (presence of [[hydrogen sulfide]]) is found from the Late Permian to the Early Triassic.<ref>{{cite journal |last1=Wang |first1=Han |last2=He |first2=Weihong |last3=Xiao |first3=Yifan |last4=Yang |first4=Tinglu |last5=Zhang |first5=Kexin |last6=Wu |first6=Huiting |last7=Huang |first7=Yafei |last8=Peng |first8=Xingfang |last9=Wu |first9=Shunbao |date=1 July 2023 |title=Stagewise collapse of biotic communities and its relations to oxygen depletion along the north margin of Nanpanjiang Basin during the Permian–Triassic transition |url=https://www.sciencedirect.com/science/article/pii/S0031018223001876 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=621 |page=111569 |doi=10.1016/j.palaeo.2023.111569 |bibcode=2023PPP...62111569W |access-date=31 May 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Hülse |first1=Dominik |last2=Lau |first2=Kimberly V. |last3=Van de Velde |first3=Sebastiaan J. |last4=Arndt |first4=Sandra |last5=Meyer |first5=Katja M. |last6=Ridgwell |first6=Andy |date=28 October 2021 |title=End-Permian marine extinction due to temperature-driven nutrient recycling and euxinia |url=https://www.nature.com/articles/s41561-021-00829-7?error=cookies_not_supported&code=65341cdd-dd3e-41c1-b577-b859ae06d053 |journal=[[Nature Geoscience]] |volume=14 |issue=11 |pages=862–867 |doi=10.1038/s41561-021-00829-7 |bibcode=2021NatGe..14..862H |hdl=2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/334194 |s2cid=240076553 |access-date=8 January 2023}}</ref><ref>{{Cite journal |last=Benton |first=Michael James |date=January 2008 |title=Presidential Address 2007: The end-Permian mass extinction — events on land in Russia |url=https://linkinghub.elsevier.com/retrieve/pii/S0016787808803136 |journal=[[Proceedings of the Geologists' Association]] |language=en |volume=119 |issue=2 |pages=119–136 |doi=10.1016/S0016-7878(08)80313-6 |bibcode=2008PrGA..119..119B |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Throughout most of the [[Tethys Ocean|Tethys]] and [[Panthalassic]] Oceans, evidence for anoxia appears at the extinction event, including small pyrite [[framboid]]s,<ref name=WignallandTwitchett2002>{{cite book |last1=Wignall |first1=Paul Barry |last2=Twitchett |first2=Richard J. |editor-last1=Koeberl |editor-first1=Christian |editor-last2=MacLeod |editor-first2=Kenneth G. |date=2002 |title=Catastrophic Events and Mass Extinction: Impacts and Beyond |chapter=Extent, duration, and nature of the Permian-Triassic superanoxic event |chapter-url=https://www.researchgate.net/publication/279396802 |access-date=17 February 2024 |publisher=Geological Society of America Special Papers No. 356 |pages=395–413 |doi=10.1130/0-8137-2356-6.395 |isbn=9780813723563 |ol=11351081M |bibcode=2002GSASP.356..395W }}</ref><ref>{{Cite journal |last1=Wei |first1=Hengye |last2=Algeo |first2=Thomas J. |last3=Yu |first3=Hao |last4=Wang |first4=Jiangguo |last5=Guo |first5=Chuan |last6=Shi |first6=Guo |date=15 April 2015 |title=Episodic euxinia in the Changhsingian (late Permian) of South China: Evidence from framboidal pyrite and geochemical data |url=https://linkinghub.elsevier.com/retrieve/pii/S0037073815000494 |journal=Sedimentary Geology |language=en |volume=319 |pages=78–97 |doi=10.1016/j.sedgeo.2014.11.008 |bibcode=2015SedG..319...78W |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> negative δ<sup>238</sup>U excursions,<ref name="BrenneckaEtAl2011" /><ref>{{cite journal |last1=Wang |first1=Wen-qian |last2=Zhang |first2=Feifei |last3=Shen |first3=Shu-zhong |last4=Bizzarro |first4=Martin |last5=Garbelli |first5=Claudio |last6=Zheng |first6=Quan-feng |last7=Zhang |first7=Yi-chun |last8=Yuan |first8=Dong-xun |last9=Shi |first9=Yu-kun |last10=Cao |first10=Mengchun |last11=Dahl |first11=Tais W. |date=15 September 2022 |title=Constraining marine anoxia under the extremely oxygenated Permian atmosphere using uranium isotopes in calcitic brachiopods and marine carbonates |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X22003508 |journal=[[Earth and Planetary Science Letters]] |volume=594 |page=117714 |doi=10.1016/j.epsl.2022.117714 |bibcode=2022E&PSL.59417714W |s2cid=250941149 |access-date=31 May 2023|url-access=subscription }}</ref> negative δ<sup>15</sup>N excursions,<ref>{{cite journal |last1=Luo |first1=Genming |last2=Wang |first2=Yongbiao |last3=Algeo |first3=Thomas J. |last4=Kump |first4=Lee R. |last5=Bai |first5=Xiao |last6=Yang |first6=Hao |last7=Yao |first7=Le |last8=Xie |first8=Shucheng |date=1 July 2011 |title=Enhanced nitrogen fixation in the immediate aftermath of the latest Permian marine mass extinction |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/39/7/647/130602/Enhanced-nitrogen-fixation-in-the-immediate |journal=[[Geology (journal)|Geology]] |volume=39 |issue=7 |pages=647–650 |doi=10.1130/G32024.1 |bibcode=2011Geo....39..647L |access-date=26 May 2023|url-access=subscription }}</ref> positive δ<sup>82/78</sup>Se isotope excursions,<ref>{{Cite journal |last1=Stüeken |first1=Eva E. |last2=Foriel |first2=Julien |last3=Buick |first3=Roger |last4=Schoepfer |first4=Shane D. |date=2 September 2015 |title=Selenium isotope ratios, redox changes and biological productivity across the end-Permian mass extinction |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254115002843 |journal=[[Chemical Geology]] |language=en |volume=410 |pages=28–39 |doi=10.1016/j.chemgeo.2015.05.021 |bibcode=2015ChGeo.410...28S |access-date=13 March 2024 |via=Elsevier Science Direct}}</ref> relatively positive δ<sup>13</sup>C ratios in polycyclic aromatic hydrocarbons,<ref>{{cite journal |last1=Grice |first1=Kliti |last2=Nabbefeld |first2=Birgit |last3=Maslen |first3=Ercin |date=November 2007 |title=Source and significance of selected polycyclic aromatic hydrocarbons in sediments (Hovea-3 well, Perth Basin, Western Australia) spanning the Permian–Triassic boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0146638007001581 |journal=[[Organic Geochemistry]] |volume=38 |issue=11 |pages=1795–1803 |doi=10.1016/j.orggeochem.2007.07.001 |bibcode=2007OrGeo..38.1795G |access-date=31 May 2023|url-access=subscription }}</ref> high Th/U ratios,<ref>{{cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul Barry |last3=Tong |first3=Jinnan |last4=Bond |first4=David P. G. |last5=Song |first5=Huyue |last6=Lai |first6=Xulong |last7=Zhang |first7=Kexin |last8=Wang |first8=Hongmei |last9=Chen |first9=Yanlong |date=1 November 2012 |title=Geochemical evidence from bio-apatite for multiple oceanic anoxic events during Permian–Triassic transition and the link with end-Permian extinction and recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003640 |journal=[[Earth and Planetary Science Letters]] |volume=353-354 |pages=12–21 |bibcode=2012E&PSL.353...12S |doi=10.1016/j.epsl.2012.07.005 |access-date=13 January 2023|url-access=subscription }}</ref><ref name="BrenneckaEtAl2011">{{cite journal |last1=Brennecka |first1=Gregory A. |last2=Herrmann |first2=Achim D. |last3=Algeo |first3=Thomas J. |last4=Anbar |first4=Ariel D. |date=10 October 2011 |title=Rapid expansion of oceanic anoxia immediately before the end-Permian mass extinction |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |volume=108 |issue=43 |pages=17631–17634 |doi=10.1073/pnas.1106039108 |pmid=21987794 |pmc=3203792 |doi-access=free }}</ref> positive Ce/Ce* anomalies,<ref>{{cite journal |last1=Müller |first1=J. |last2=Sun |first2=Y. D. |last3=Fang |first3=F. |last4=Regulous |first4=M. |last5=Joachimski |first5=Michael M. |date=March 2023 |title=Manganous water column in the Tethys Ocean during the Permian-Triassic transition |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818123000401 |journal=[[Global and Planetary Change]] |volume=222 |page=104067 |doi=10.1016/j.gloplacha.2023.104067 |bibcode=2023GPC...22204067M |s2cid=256800036 |access-date=26 June 2023|url-access=subscription }}</ref> depletions of molybdenum, uranium, and vanadium from seawater,<ref>{{Cite journal |last1=Xiang |first1=Lei |last2=Zhang |first2=Hua |last3=Schoepfer |first3=Shane D. |last4=Cao |first4=Chang-qun |last5=Zheng |first5=Quan-feng |last6=Yuan |first6=Dong-xun |last7=Cai |first7=Yao-feng |last8=Shen |first8=Shu-zhong |date=15 April 2020 |title=Oceanic redox evolution around the end-Permian mass extinction at Meishan, South China |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018219306078 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=544 |pages=109626 |doi=10.1016/j.palaeo.2020.109626 |bibcode=2020PPP...54409626X |access-date=1 August 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> and fine laminations in sediments.<ref name=WignallandTwitchett2002 /> However, evidence for anoxia precedes the extinction at some other sites, including [[Spiti]], [[India]],<ref>{{cite journal |last1=Stebbins |first1=Alan |last2=Williams |first2=Jeremy |last3=Brookfield |first3=Michael |last4=Nye Jr. |first4=Steven W. |last5=Hannigan |first5=Robyn |date=15 February 2019 |title=Frequent euxinia in southern Neo-Tethys Ocean prior to the end-Permian biocrisis: Evidence from the Spiti region, India |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=516 |pages=1–10 |doi=10.1016/j.palaeo.2018.11.030 |bibcode=2019PPP...516....1S |s2cid=134724104 |doi-access=free }}</ref> Shangsi, China,<ref>{{cite journal |last1=Zhang |first1=Li-Jun |last2=Zhang |first2=Xin |last3=Buatois |first3=Luis A. |last4=Mángano |first4=M. Gabriela |last5=Shi |first5=Guang R. Shi |last6=Gong |first6=Yi-Ming |last7=Qi |first7=Yong-An |date=December 2000 |title=Periodic fluctuations of marine oxygen content during the latest Permian |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818120302174 |journal=[[Global and Planetary Change]] |volume=195 |page=103326 |doi=10.1016/j.gloplacha.2020.103326 |s2cid=224881713 |access-date=2 March 2023|url-access=subscription }}</ref> [[Meishan]], China,<ref name=Caoetal2009>{{cite journal |last=Cao |first=Changqun |author2=Gordon D. Love |author3=Lindsay E. Hays |author4=Wei Wang |author5=Shuzhong Shen |author6=Roger E. Summons |title=Biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end-Permian mass extinction event |journal=[[Earth and Planetary Science Letters]] |year=2009 |volume=281 |issue=3–4 |pages=188–201 |doi=10.1016/j.epsl.2009.02.012 |bibcode=2009E&PSL.281..188C
}}</ref> Opal Creek, [[Alberta]],<ref>{{cite journal |last1=Schoepfer |first1=Shane D. |last2=Henderson |first2=Charles M. |last3=Garrison |first3=Geoffrey H. |last4=Ward |first4=Peter Douglas |date=1 January 2012 |title=Cessation of a productive coastal upwelling system in the Panthalassic Ocean at the Permian–Triassic Boundary |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018211005281 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=313-314 |pages=181–188 |doi=10.1016/j.palaeo.2011.10.019 |bibcode=2012PPP...313..181S |access-date=21 December 2022|url-access=subscription }}</ref> and Kap Stosch, Greenland.<ref name=Hays2012>{{cite journal|last=Hays|first=Lindsay|author2=Kliti Grice |author3=Clinton B. Foster |author4=Roger E. Summons |title=Biomarker and isotopic trends in a Permian–Triassic sedimentary section at Kap Stosch, Greenland|journal=[[Organic Geochemistry]]|year=2012|volume=43|pages=67–82|doi=10.1016/j.orggeochem.2011.10.010|bibcode=2012OrGeo..43...67H |url=https://espace.curtin.edu.au/bitstream/20.500.11937/26597/2/170581_StreamGate.pdf|hdl=20.500.11937/26597|hdl-access=free}}</ref> Biogeochemical evidence also points to the presence of euxinia during the PTME.<ref>{{cite journal |last1=Hays |first1=Lindsay E. |last2=Beatty |first2=Tyler |last3=Henderson |first3=Charles M. |last4=Love |first4=Gordon D. |last5=Summons |first5=Roger E. |date=January–September 2007 |title=Evidence for photic zone euxinia through the end-Permian mass extinction in the Panthalassic Ocean (Peace River Basin, Western Canada) |url=https://www.sciencedirect.com/science/article/abs/pii/S1871174X07000169 |journal=[[Palaeoworld]] |volume=16 |issue=1–3 |pages=39–50 |doi=10.1016/j.palwor.2007.05.008 |access-date=23 May 2023|url-access=subscription }}</ref> Biomarkers for green sulfur bacteria, such as isorenieratane, the [[Diagenesis|diagenetic]] product of [[isorenieratene]], are widely used as indicators of [[photic zone]] euxinia because green sulfur [[bacteria]] require both sunlight and hydrogen sulfide to survive. Their abundance in sediments from the P–T boundary indicates euxinic conditions were present even in the shallow waters of the photic zone.<ref>{{cite journal |last1=Xie |first1=Shucheng |last2=Algeo |first2=Thomas J. |last3=Zhou |first3=Wenfeng |last4=Ruan |first4=Xiaoyan |last5=Luo |first5=Genming |last6=Huang |first6=Junhua |last7=Yan |first7=Jiaxin |date=15 February 2017 |title=Contrasting microbial community changes during mass extinctions at the Middle/Late Permian and Permian/Triassic boundaries |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X16307282 |journal=[[Earth and Planetary Science Letters]] |volume=460 |pages=180–191 |doi=10.1016/j.epsl.2016.12.015 |bibcode=2017E&PSL.460..180X |access-date=4 January 2023|url-access=subscription }}</ref><ref>{{Cite journal |last1=Luo |first1=Genming |last2=Huang |first2=Junhuang |last3=Xie |first3=Shucheng |last4=Wignall |first4=Paul Barry |last5=Tang |first5=Xinyan |last6=Huang |first6=Xianyu |last7=Yin |first7=Hongfu |date=13 February 2009 |title=Relationships between carbon isotope evolution and variation of microbes during the Permian–Triassic transition at Meishan Section, South China |url=http://link.springer.com/10.1007/s00531-009-0421-9 |journal=[[International Journal of Earth Sciences]] |language=en |volume=99 |issue=4 |pages=775–784 |doi=10.1007/s00531-009-0421-9 |issn=1437-3254 |access-date=1 August 2024 |via=Springer Link|url-access=subscription }}</ref> Negative mercury isotope excursions further bolster evidence for extensive euxinia during the PTME.<ref>{{cite journal |last1=Sun |first1=Ruoyu |last2=Liu |first2=Yi |last3=Sonke |first3=Jeroen E. |last4=Feifei |first4=Zhang |last5=Zhao |first5=Yaqiu |last6=Zhang |first6=Yonggen |last7=Chen |first7=Jiubin |last8=Liu |first8=Cong-Qiang |last9=Shen |first9=Shuzhong |last10=Anbar |first10=Ariel D. |last11=Zheng |first11=Wang |date=8 May 2023 |title=Mercury isotope evidence for marine photic zone euxinia across the end-Permian mass extinction |journal=[[Communications Earth & Environment]] |volume=4 |issue=1 |page=159 |doi=10.1038/s43247-023-00821-6 |bibcode=2023ComEE...4..159S |s2cid=258577845 |doi-access=free }}</ref> The disproportionate extinction of high-latitude marine species provides further evidence for oxygen depletion as a killing mechanism; low-latitude species living in warmer, less oxygenated waters are naturally better adapted to lower levels of oxygen and are able to migrate to higher latitudes during periods of global warming, whereas high-latitude organisms are unable to escape from warming, hypoxic waters at the poles.<ref name="PennDeutschPayneSperling2018">{{cite journal |last1=Penn |first1=Justin L. |last2=Deutsch |first2=Curtis |last3=Payne |first3=Jonathan L. |last4=Sperling |first4=Erik A. |date=7 December 2018 |title=Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction |journal=[[Science (journal)|Science]] |volume=362 |issue=6419 |pages=1–6 |doi=10.1126/science.aat1327 |pmid=30523082 |bibcode=2018Sci...362.1327P |s2cid=54456989 |doi-access=free }}</ref> Evidence of a lag between volcanic mercury inputs and biotic turnovers provides further support for anoxia and euxinia as the key killing mechanism, because extinctions would be expected to be synchronous with volcanic mercury discharge if volcanism and hypercapnia was the primary driver of extinction.<ref>{{cite journal |last1=Shen |first1=Jun |last2=Chen |first2=Jiubin |last3=Algeo |first3=Thomas J. |last4=Yuan |first4=Shengliu |last5=Feng |first5=Qinglai |last6=Yu |first6=Jianxin |last7=Zhou |first7=Lian |last8=O'Connell |first8=Brennan |last9=Planavsky |first9=Noah J. |date=5 April 2019 |title=Evidence for a prolonged Permian–Triassic extinction interval from global marine mercury records |journal=[[Nature Communications]] |volume=10 |issue=1 |page=1563 |doi=10.1038/s41467-019-09620-0 |pmid=30952859 |pmc=6450928 |bibcode=2019NatCo..10.1563S }}</ref> The sequence of extinctions in some sections, with deep water organisms being affected first followed by shallow water and then by bottom water organisms, is believed to reflect the migration of oxygen minimum zones.<ref>{{Cite journal |last1=He |first1=Weihong |last2=Weldon |first2=Elizabeth A. |last3=Yang |first3=Tinglu |last4=Wang |first4=Han |last5=Xiao |first5=Yifan |last6=Zhang |first6=Kexin |last7=Peng |first7=Xingfang |last8=Feng |first8=Qinglai |date=1 September 2024 |title=An end-Permian two-stage extinction pattern in the deep-water Dongpan Section, and its relationship to the migration and vertical expansion of the oxygen minimum zone in the South China Basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018224002967 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=649 |pages=112307 |doi=10.1016/j.palaeo.2024.112307 |bibcode=2024PPP...64912307H |access-date=13 October 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Models of [[ocean chemistry]] suggest that anoxia and euxinia were closely associated with [[hypercapnia]]. This suggests that poisoning from [[hydrogen sulfide]], anoxia, and hypercapnia acted together as a killing mechanism. Hypercapnia best explains the selectivity of the extinction, but anoxia and euxinia probably contributed to the high mortality of the event.<ref name="Meyers2008">{{cite journal |last=Meyers |first=Katja |author2=L.R. Kump |author3=A. Ridgwell |date=September 2008 |title=Biogeochemical controls on photic-zone euxinia during the end-Permian mass extinction |journal=[[Geology (journal)|Geology]] |volume=36 |issue=9 |pages=747–750 |bibcode=2008Geo....36..747M |doi=10.1130/g24618a.1}}</ref>

The sequence of events leading to anoxic oceans may have been triggered by carbon dioxide emissions from the eruption of the Siberian Traps.<ref name="EPMEPETM" /> In that scenario, warming from the enhanced greenhouse effect would reduce the solubility of oxygen in seawater, causing the concentration of oxygen to decline. Increased coastal evaporation would have caused the formation of warm saline bottom water (WSBW) depleted in oxygen and nutrients, which spread across the world through the deep oceans. The influx of WSBW caused thermal expansion of water that raised sea levels, bringing anoxic waters onto shallow shelfs and enhancing the formation of WSBW in a positive feedback loop.<ref>{{cite journal |last1=Kidder |first1=David L. |last2=Worsley |first2=Thomas R. |date=15 February 2004 |title=Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018203006679 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=203 |issue=3–4 |pages=207–237 |doi=10.1016/S0031-0182(03)00667-9 |bibcode=2004PPP...203..207K |access-date=23 May 2023|url-access=subscription }}</ref> The flux of terrigeneous material into the oceans increased as a result of soil erosion, which would have facilitated increased eutrophication;<ref>{{cite journal |last1=Sephton |first1=Mark A. |last2=Looy |first2=Cindy V. |last3=Brinkhuis |first3=Henk |last4=Wignall |first4=Paul Barry |last5=De Leeuw |first5=Jan W. |last6=Visscher |first6=Henk |date=1 December 2005 |title=Catastrophic soil erosion during the end-Permian biotic crisis |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/33/12/941/129272/Catastrophic-soil-erosion-during-the-end-Permian?redirectedFrom=fulltext |journal=[[Geology (journal)|Geology]] |volume=33 |issue=12 |pages=941–944 |doi=10.1130/G21784.1 |bibcode=2005Geo....33..941S |access-date=26 May 2023|url-access=subscription }}</ref> marine regression likewise enhanced terrigeneous material inputs.<ref>{{Cite journal |last1=Duan |first1=Xiong |last2=Shi |first2=Zhiqiang |date=30 May 2024 |title=Sedimentary records of sea level fall during the end-Permian in the upper Yangtze region (southern China): Implications for the mass extinction |journal=[[Heliyon]] |language=en |volume=10 |issue=10 |pages=e31226 |doi=10.1016/j.heliyon.2024.e31226 |doi-access=free |pmc=11126861 |pmid=38799747 |bibcode=2024Heliy..1031226D }}</ref> Increased chemical weathering of the continents due to warming and the acceleration of the [[water cycle]] would increase the riverine flux of nutrients to the ocean.<ref>{{cite journal |last1=Algeo |first1=Thomas J. |last2=Henderson |first2=Charles M. |last3=Tong |first3=Jinnan |last4=Feng |first4=Qinglai |last5=Yin |first5=Hongfu |last6=Tyson |first6=Richard V. |date=June 2013 |title=Plankton and productivity during the Permian–Triassic boundary crisis: An analysis of organic carbon fluxes |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818112000380 |journal=[[Global and Planetary Change]] |volume=105 |pages=52–67 |doi=10.1016/j.gloplacha.2012.02.008 |bibcode=2013GPC...105...52A |access-date=3 July 2023|url-access=subscription }}</ref> Additionally, the Siberian Traps directly fertilised the oceans with iron and phosphorus as well, triggering bioblooms and marine snowstorms. Increased [[phosphate]] levels would have supported greater primary productivity in the surface oceans.<ref>{{Cite journal |last1=Grasby |first1=Stephen E. |last2=Ardakani |first2=Omid H. |last3=Liu |first3=Xiaojun |last4=Bond |first4=David P. G. |last5=Wignall |first5=Paul Barry |last6=Strachan |first6=Lorna J. |date=29 November 2023 |title=Marine snowstorm during the Permian−Triassic mass extinction |journal=[[Geology (journal)|Geology]] |volume=52 |issue=2 |pages=120–124 |language=en |doi=10.1130/G51497.1 |issn=0091-7613 |doi-access=free }}</ref> The increase in organic matter production would have caused more organic matter to sink into the deep ocean, where its respiration would further decrease oxygen concentrations. Once anoxia became established, it would have been sustained by a [[Positive feedback|positive feedback loop]] because deep water anoxia tends to increase the recycling efficiency of phosphate, leading to even higher productivity.<ref>{{cite journal |last1=Schobben |first1=Martin |last2=Foster |first2=William J. |last3=Sleveland |first3=Arve R. N. |last4=Zuchuat |first4=Valentin |last5=Svensen |first5=Henrik H. |last6=Planke |first6=Sverre |last7=Bond |first7=David P. G. |last8=Marcelis |first8=Fons |last9=Newton |first9=Robert J. |last10=Wignall |first10=Paul Barry |last11=Poulton |first11=Simon W. |date=17 August 2020 |title=A nutrient control on marine anoxia during the end-Permian mass extinction |url=https://www.nature.com/articles/s41561-020-0622-1?error=cookies_not_supported&code=bd1d48f1-9898-484a-9c4d-3329db200edb |journal=[[Nature Geoscience]] |volume=13 |issue=9 |pages=640–646 |doi=10.1038/s41561-020-0622-1 |bibcode=2020NatGe..13..640S |hdl=1874/408736 |s2cid=221146234 |access-date=8 January 2023|hdl-access=free }}</ref> Along the Panthalassan coast of South China, oxygen decline was also driven by large-scale upwelling of deep water enriched in various nutrients, causing this region of the ocean to be hit by especially severe anoxia.<ref>{{cite journal |last1=Liao |first1=Wei |last2=Bond |first2=David P. G. |last3=Wang |first3=Yongbiao |last4=He |first4=Lei |last5=Yang |first5=Hao |last6=Weng |first6=Zeting |last7=Li |first7=Guoshan |date=15 November 2017 |title=An extensive anoxic event in the Triassic of the South China Block: A pyrite framboid study from Dajiang and its implications for the cause(s) of oxygen depletion |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821630699X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=486 |pages=86–95 |doi=10.1016/j.palaeo.2016.11.012 |bibcode=2017PPP...486...86L |access-date=8 May 2023}}</ref> Convective overturn helped facilitate the expansion of anoxia throughout the water column.<ref>{{cite journal |last1=Fio |first1=Karmen |last2=Spangenberg |first2=Jorge E. |last3=Vlahović |first3=Igor |last4=Sremac |first4=Jasenka |last5=Velić |first5=Ivo |last6=Mrinjek |first6=Ervin |date=1 November 2010 |title=Stable isotope and trace element stratigraphy across the Permian–Triassic transition: A redefinition of the boundary in the Velebit Mountain, Croatia |url=https://www.sciencedirect.com/science/article/abs/pii/S0009254110003013 |journal=[[Chemical Geology]] |volume=278 |issue=1–2 |pages=38–57 |doi=10.1016/j.chemgeo.2010.09.001 |bibcode=2010ChGeo.278...38F |access-date=24 April 2023|url-access=subscription }}</ref> A severe [[anoxic event]] at the end of the Permian would have allowed [[sulfate-reducing bacteria]] to thrive, causing the production of large amounts of hydrogen sulfide in the anoxic ocean, turning it euxinic.<ref name="EPMEPETM">{{cite journal |last1=Saunders |first1=Andrew D. |date=9 June 2015 |title=Two LIPs and two Earth-system crises: the impact of the North Atlantic Igneous Province and the Siberian Traps on the Earth-surface carbon cycle |url=https://pubs.geoscienceworld.org/geolmag/article-abstract/153/2/201/251172/Two-LIPs-and-two-Earth-system-crises-the-impact-of?redirectedFrom=fulltext |journal=[[Geological Magazine]] |volume=153 |issue=2 |pages=201–222 |doi=10.1017/S0016756815000175 |s2cid=131273374 |access-date=26 May 2023|hdl=2381/32095 |hdl-access=free }}</ref> In some regions, anoxia briefly disappeared when transient cold snaps resulting from volcanic sulphur emissions occurred.<ref>{{Cite journal |last1=Newby |first1=Sean M. |last2=Owens |first2=Jeremy D. |last3=Schoepfer |first3=Shane D. |last4=Algeo |first4=Thomas J. |date=2 August 2021 |title=Transient ocean oxygenation at end-Permian mass extinction onset shown by thallium isotopes |url=https://www.nature.com/articles/s41561-021-00802-4 |journal=[[Nature Geoscience]] |language=en |volume=14 |issue=9 |pages=678–683 |doi=10.1038/s41561-021-00802-4 |bibcode=2021NatGe..14..678N |s2cid=236780878 |issn=1752-0908 |access-date=27 December 2023|url-access=subscription }}</ref>

The persistence of anoxia through the Early Triassic may explain the slow recovery of marine life and low levels of biodiversity after the extinction,<ref>{{cite journal |last1=Shen |first1=Jun |last2=Schoepfer |first2=Shane D. |last3=Feng |first3=Qinglai |last4=Zhou |first4=Lian |last5=Yu |first5=Jianxin |last6=Song |first6=Huyue |last7=Wei |first7=Hengye |last8=Algeo |first8=Thomas J. |date=October 2015 |title=Marine productivity changes during the end-Permian crisis and Early Triassic recovery |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825214001925 |journal=[[Earth-Science Reviews]] |volume=149 |pages=136–162 |doi=10.1016/j.earscirev.2014.11.002 |bibcode=2015ESRv..149..136S |access-date=20 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Wignall |first1=Paul Barry |last2=Hallam |first2=Anthony |date=May 1992 |title=Anoxia as a cause of the Permian/Triassic mass extinction: facies evidence from northern Italy and the western United States |url=https://www.sciencedirect.com/science/article/abs/pii/0031018292901825 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=93 |issue=1–2 |pages=21–46 |doi=10.1016/0031-0182(92)90182-5 |bibcode=1992PPP....93...21W |access-date=20 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Chen |first1=Zhong-Qiang |last2=Yang |first2=Hao |last3=Luo |first3=Mao |last4=Benton |first4=Michael James |last5=Kaiho |first5=Kunio |last6=Zhao |first6=Laishi |last7=Huang |first7=Yuangeng |last8=Zhang |first8=Kexing |last9=Fang |first9=Yuheng |last10=Jiang |first10=Haishui |last11=Qiu |first11=Huan |last12=Li |first12=Yang |last13=Tu |first13=Chengyi |last14=Shi |first14=Lei |last15=Zhang |first15=Lei |last16=Feng |first16=Xueqian |last17=Chen |first17=Long |date=October 2015 |title=Complete biotic and sedimentary records of the Permian–Triassic transition from Meishan section, South China: Ecologically assessing mass extinction and its aftermath |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825214001846 |journal=[[Earth-Science Reviews]] |volume=149 |pages=67–107 |doi=10.1016/j.earscirev.2014.10.005 |bibcode=2015ESRv..149...67C |hdl=1983/d2b89cc3-b0a8-41b5-a220-b3d7d75687e0 |access-date=14 January 2023|hdl-access=free }}</ref> particularly that of benthic organisms.<ref>{{cite journal |last1=Pietsch |first1=Carlie |last2=Mata |first2=Scott A. |last3=Bottjer |first3=David J. |date=1 April 2014 |title=High temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end-Permian mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214000583 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=399 |pages=98–113 |doi=10.1016/j.palaeo.2014.02.011 |bibcode=2014PPP...399...98P |access-date=2 April 2023|url-access=subscription }}</ref><ref name="OceanicAnoxiaAndTheEndPermianMassExtinction" /> Anoxia disappeared from shallow waters more rapidly than the deep ocean.<ref>{{Cite journal |last1=Algeo |first1=Thomas J. |last2=Chen |first2=Zhong Qiang |last3=Fraiser |first3=Margaret L. |last4=Twitchett |first4=Richard J. |date=15 July 2011 |title=Terrestrial–marine teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems |url=https://www.sciencedirect.com/science/article/pii/S0031018211000149 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |series=Permian - Triassic ecosystems: collapse and rebuilding |volume=308 |issue=1 |pages=1–11 |doi=10.1016/j.palaeo.2011.01.011 |bibcode=2011PPP...308....1A |issn=0031-0182 |access-date=24 November 2023|url-access=subscription }}</ref> Reexpansions of oxygen-minimum zones did not cease until the late Spathian, periodically setting back and restarting the biotic recovery process.<ref>{{cite journal |last1=Tian |first1=Li |last2=Tong |first2=Jinnan |last3=Algeo |first3=Thomas J. |last4=Song |first4=Haijun |last5=Song |first5=Huyue |last6=Chu |first6=Daoliang |last7=Shi |first7=Lei |last8=Bottjer |first8=David J. |date=15 October 2014 |title=Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214003733 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=412 |pages=68–79 |doi=10.1016/j.palaeo.2014.07.018 |bibcode=2014PPP...412...68T |access-date=8 May 2023|url-access=subscription }}</ref> The decline in continental weathering towards the end of the Spathian at last began ameliorating marine life from recurrent anoxia.<ref>{{Cite journal |last1=Song |first1=Haijun |last2=Wignall |first2=Paul Barry |last3=Tong |first3=Jinnan |last4=Song |first4=Huyue |last5=Chen |first5=Jing |last6=Chu |first6=Daoliang |last7=Tian |first7=Li |last8=Luo |first8=Mao |last9=Zong |first9=Keqing |last10=Chen |first10=Yanlong |last11=Lai |first11=Xulong |last12=Zhang |first12=Kexin |last13=Wang |first13=Hongmei |date=15 August 2015 |title=Integrated Sr isotope variations and global environmental changes through the Late Permian to early Late Triassic |url=https://www.sciencedirect.com/science/article/pii/S0012821X15003337 |journal=[[Earth and Planetary Science Letters]] |volume=424 |pages=140–147 |doi=10.1016/j.epsl.2015.05.035 |bibcode=2015E&PSL.424..140S |issn=0012-821X |access-date=24 November 2023}}</ref> In some regions of Panthalassa, pelagic zone anoxia continued to recur as late as the Anisian,<ref>{{Cite journal |last1=Muto |first1=Shun |last2=Takahashi |first2=Satoshi |last3=Yamakita |first3=Satoshi |last4=Suzuki |first4=Noritoshi |last5=Suzuki |first5=Nozomi |last6=Aita |first6=Yoshiaki |date=15 January 2018 |title=High sediment input and possible oceanic anoxia in the pelagic Panthalassa during the latest Olenekian and early Anisian: Insights from a new deep-sea section in Ogama, Tochigi, Japan |url=https://www.sciencedirect.com/science/article/pii/S0031018217304443 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=490 |pages=687–707 |doi=10.1016/j.palaeo.2017.11.060 |bibcode=2018PPP...490..687M |issn=0031-0182 |access-date=24 November 2023|url-access=subscription }}</ref> probably due to increased productivity and a return of aeolian upwelling.<ref>{{Cite journal |last1=Woods |first1=Adam D. |last2=Zonneveld |first2=John-Paul |last3=Wakefield |first3=Ryan |date=13 December 2023 |title=Hyperthermal-driven anoxia and reduced productivity in the aftermath of the Permian-Triassic mass extinction: a case study from Western Canada |journal=[[Frontiers in Earth Science]] |volume=11 |doi=10.3389/feart.2023.1323413 |doi-access=free |bibcode=2023FrEaS..1123413W |issn=2296-6463 }}</ref> Some sections show a rather quick return to oxic water column conditions, however, so for how long anoxia persisted remains debated.<ref>{{cite journal |last1=Li |first1=Guoshan |last2=Wang |first2=Yongbiao |last3=Shi |first3=Guang R. |last4=Liao |first4=Wei |last5=Yu |first5=Lixue |date=15 April 2016 |title=Fluctuations of redox conditions across the Permian–Triassic boundary—New evidence from the GSSP section in Meishan of South China |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821500560X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=448 |pages=48–58 |doi=10.1016/j.palaeo.2015.09.050 |bibcode=2016PPP...448...48L |access-date=26 May 2023|url-access=subscription }}</ref> The volatility of the Early Triassic sulphur cycle suggests marine life continued to face returns of euxinia as well.<ref>{{cite journal |last1=Schobben |first1=Martin |last2=Stebbins |first2=Alan |last3=Algeo |first3=Thomas J. |last4=Strauss |first4=Harald |last5=Leda |first5=Lucyna |last6=Haas |first6=János |last7=Struck |first7=Ulrich |last8=Korn |first8=Dieter |last9=Korte |first9=Christoph |date=15 November 2017 |title=Volatile earliest Triassic sulfur cycle: A consequence of persistent low seawater sulfate concentrations and a high sulfur cycle turnover rate? |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018217301931 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=486 |pages=74–85 |doi=10.1016/j.palaeo.2017.02.025 |bibcode=2017PPP...486...74S |access-date=26 May 2023|url-access=subscription }}</ref>

Some scientists have challenged the anoxia hypothesis on the grounds that long-lasting anoxic conditions could not have been supported if Late Permian thermohaline ocean circulation conformed to the "thermal mode" characterised by cooling at high latitudes. Anoxia may have persisted under a "haline mode" in which circulation was driven by subtropical evaporation, although the "haline mode" is highly unstable and was unlikely to have represented Late Permian oceanic circulation.<ref name="ZhangEtAl2001">{{cite journal| vauthors =Zhang R, Follows MJ, Grotzinger JP, Marshall J| title =Could the Late Permian deep ocean have been anoxic?| journal =[[Paleoceanography and Paleoclimatology]]| volume =16| issue =3| pages =317–329| year =2001| doi =10.1029/2000PA000522| bibcode =2001PalOc..16..317Z| doi-access =free}}</ref>

Oxygen depletion via extensive microbial blooms also played a role in the biological collapse of not just marine ecosystems but freshwater ones as well. Persistent lack of oxygen after the extinction event itself helped delay biotic recovery for much of the Early Triassic epoch.<ref>{{cite journal |last1=Mays |first1=Chris |last2=McLoughlin |first2=Stephen |last3=Frank |first3=Tracy D. |last4=Fielding |first4=Christopher R. |last5=Slater |first5=Sam M. |last6=Vajda |first6=Vivi |date=17 September 2021 |title=Lethal microbial blooms delayed freshwater ecosystem recovery following the end-Permian extinction |journal=[[Nature Communications]] |volume=12 |issue=1 |page=5511 |doi=10.1038/s41467-021-25711-3 |pmid=34535650 |pmc=8448769 |bibcode=2021NatCo..12.5511M }}</ref>

=== Aridification ===
Increasing continental aridity, a trend well underway even before the PTME as a result of the coalescence of the supercontinent Pangaea, was drastically exacerbated by terminal Permian volcanism and global warming.<ref name="SmithBothaViglietti2022">{{cite journal |last1=Smith |first1=Roger M. H. |last2=Botha |first2=Jennifer |last3=Viglietti |first3=Pia A. |date=15 October 2022 |title=Taphonomy of drought afflicted tetrapods in the Early Triassic Karoo Basin, South Africa |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018222003777 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=604 |page=111207 |doi=10.1016/j.palaeo.2022.111207 |bibcode=2022PPP...60411207S |s2cid=251781291 |access-date=23 May 2023|url-access=subscription }}</ref> The combination of global warming and drying generated an increased incidence of wildfires.<ref>{{cite journal |last1=Song |first1=Yi |last2=Tian |first2=Yuan |last3=Yu |first3=Jianxin |last4=Algeo |first4=Thomas J. |last5=Luo |first5=Genming |last6=Chu |first6=Daoliang |last7=Xie |first7=Shucheng |date=August 2022 |title=Wildfire response to rapid climate change during the Permian-Triassic biotic crisis |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818122001394 |journal=[[Global and Planetary Change]] |volume=215 |page=103872 |doi=10.1016/j.gloplacha.2022.103872 |bibcode=2022GPC...21503872S |s2cid=249857664 |access-date=23 May 2023|url-access=subscription }}</ref> Tropical coastal swamp floras such as those in South China may have been very detrimentally impacted by the increase in wildfires,<ref name="EcologicalDisturbanceTropicalPeatlands">{{cite journal |last1=Chu |first1=Daoliang |last2=Grasby |first2=Stephen E. |last3=Song |first3=Haijun |last4=Dal Corso |first4=Jacopo |last5=Wang |first5=Yao |last6=Mather |first6=Tamsin A. |last7=Wu |first7=Yuyang |last8=Song |first8=Huyue |last9=Shu |first9=Wenchao |last10=Tong |first10=Jinnan |last11=Wignall |first11=Paul Barry |date=3 January 2020 |title=Ecological disturbance in tropical peatlands prior to marine Permian-Triassic mass extinction |journal=[[Geology (journal)|Geology]] |volume=48 |issue=3 |pages=288–292 |doi=10.1130/G46631.1 |bibcode=2020Geo....48..288C |s2cid=214468383 |doi-access=free }}</ref> though it is ultimately unclear if an increase in wildfires played a role in driving taxa to extinction.<ref>{{cite journal |last1=Benton |first1=Michael James |last2=Newell |first2=Andrew J. |date=May 2014 |title=Impacts of global warming on Permo-Triassic terrestrial ecosystems |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X12004169 |journal=[[Gondwana Research]] |volume=25 |issue=4 |pages=1308–1337 |doi=10.1016/j.gr.2012.12.010 |bibcode=2014GondR..25.1308B |access-date=26 May 2023|url-access=subscription }}</ref>

Aridification trends varied widely in their tempo and regional impact. Analysis of the fossil river deposits of the floodplains of the Karoo Basin indicate a shift from [[meander]]ing to [[braided river]] patterns, indicating a very abrupt drying of the climate.<ref>{{cite journal |last=Smith |first=R.M.H. |date=16 November 1999 |title=Changing fluvial environments across the Permian–Triassic boundary in the Karoo Basin, South Africa and possible causes of tetrapod extinctions |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=117 |issue=1–2 |pages=81–104 |bibcode=1995PPP...117...81S |doi=10.1016/0031-0182(94)00119-S}}</ref> The climate change may have taken as little as 100,000 years, prompting the extinction of the unique ''Glossopteris'' flora and its associated herbivores, followed by the carnivorous guild.<ref>{{cite book |last=Chinsamy-Turan |title=Forerunners of mammals : radiation, histology, biology |publisher=[[Indiana University Press]] |year=2012 |isbn=978-0-253-35697-0 |editor=Anusuya |location=Bloomington}}</ref> A pattern of aridity-induced extinctions that progressively ascended up the food chain has been deduced from Karoo Basin biostratigraphy.<ref name="SmithBotha2014" /> Evidence for aridification in the Karoo across the Permian-Triassic boundary is not, however, universal, as some palaeosol evidence indicates a wettening of the local climate during the transition between the two geologic periods.<ref>{{cite journal |last1=Gastaldo |first1=Robert A. |last2=Kus |first2=Kaci |last3=Tabor |first3=Neil |last4=Neveling |first4=Johann |date=26 June 2020 |title=Calcic Vertisols in the upper Daptocephalus Assemblage Zone, Balfour Formation, Karoo Basin, South Africa: Implications for Late Permian Climate |url=https://pubs.geoscienceworld.org/sepm/jsedres/article-abstract/90/6/609/587564/Calcic-Vertisols-in-the-upper-Daptocephalus |journal=[[Journal of Sedimentary Research]] |volume=90 |issue=6 |pages=609–628 |doi=10.2110/jsr.2020.32 |bibcode=2020JSedR..90..609G |s2cid=221865490 |access-date=31 May 2023|url-access=subscription }}</ref> Evidence from the [[Sydney Basin]] of eastern Australia, on the other hand, suggests that the expansion of semi-arid and arid climatic belts across Pangaea was not immediate but was instead a gradual, prolonged process. Apart from the disappearance of [[peatland]]s, there was little evidence of significant sedimentological changes in depositional style across the Permian-Triassic boundary.<ref name="Fielding2020">{{cite journal |last1=Fielding |first1=Christopher R. |last2=Frank |first2=Tracy D. |last3=Tevyaw |first3=Allen P. |last4=Savatic |first4=Katarina |last5=Vajda |first5=Vivi |last6=McLoughlin |first6=Stephen |last7=Mays |first7=Chris |last8=Nicoll |first8=Robert S. |last9=Bocking |first9=Malcolm |last10=Crowley |first10=James L. |date=19 July 2020 |title=Sedimentology of the continental end-Permian extinction event in the Sydney Basin, eastern Australia |url=https://onlinelibrary.wiley.com/doi/10.1111/sed.12782 |journal=Sedimentology |volume=68 |issue=1 |pages=30–62 |doi=10.1111/sed.12782 |s2cid=225605914 |access-date=30 October 2022}}</ref> Instead, a modest shift to amplified seasonality and hotter summers is suggested by palaeoclimatological models based on weathering proxies from the region's Late Permian and Early Triassic deposits.<ref name="Fielding2019">{{cite journal |last1=Fielding |first1=Christopher R. |last2=Frank |first2=Tracy D. |last3=McLoughlin |first3=Stephen |last4=Vajda |first4=Vivi |last5=Mays |first5=Chris |last6=Tevyaw |first6=Allen P. |last7=Winguth |first7=Arne |last8=Winguth |first8=Cornelia |last9=Nicoll |first9=Robert S. |last10=Bocking |first10=Malcolm |last11=Crowley |first11=James L. |date=23 January 2019 |title=Age and pattern of the southern high-latitude continental end-Permian extinction constrained by multiproxy analysis |journal=[[Nature Communications]] |volume=10 |issue=385 |page=385 |doi=10.1038/s41467-018-07934-z |pmid=30674880 |pmc=6344581 |bibcode=2019NatCo..10..385F }}</ref> In the Kuznetsk Basin of southwestern Siberia, an increase in aridity led to the demise of the humid-adapted ''Cordaites'' forests in the region a few hundred thousand years before the Permian-Triassic boundary. Drying of this basin has been attributed to a broader poleward shift of drier, more arid climates during the late Changhsingian before the more abrupt main phase of the extinction at the Permian-Triassic boundary that disproportionately affected tropical and subtropical species.<ref name="DavydovEtAl2021PPP" />

The persistence of hyperaridity varied regionally as well. In the North China Basin, highly arid climatic conditions are recorded during the latest Permian, near the Permian-Triassic boundary, with a swing towards increased precipitation during the Early Triassic, the latter likely assisting biotic recovery following the mass extinction.<ref name="YuEtAl2022">{{cite journal |last1=Yu |first1=Yingyue |last2=Tian |first2=Li |last3=Chu |first3=Daoliang |last4=Song |first4=Huyue |last5=Guo |first5=Wenwei |last6=Tong |first6=Jinnan |date=1 January 2022 |title=Latest Permian–Early Triassic paleoclimatic reconstruction by sedimentary and isotopic analyses of paleosols from the Shichuanhe section in central North China Basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018221005113 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=585 |page=110726 |doi=10.1016/j.palaeo.2021.110726 |bibcode=2022PPP...58510726Y |s2cid=239498183 |access-date=6 November 2022|url-access=subscription }}</ref><ref name="ZhuEtAl2022">{{cite journal |last1=Zhu |first1=Zhicai |last2=Liu |first2=Yongqing |last3=Kuang |first3=Hongwei |last4=Newell |first4=Andrew J. |last5=Peng |first5=Nan |last6=Cui |first6=Mingming |last7=Benton |first7=Michael J. |date=September 2022 |title=Improving paleoenvironment in North China aided Triassic biotic recovery on land following the end-Permian mass extinction |doi-access=free |journal=[[Global and Planetary Change]] |volume=216 |page=103914 |doi=10.1016/j.gloplacha.2022.103914 |bibcode=2022GPC...21603914Z }}</ref> Elsewhere, such as in the Karoo Basin, episodes of dry climate recurred regularly in the Early Triassic, with profound effects on terrestrial tetrapods.<ref name="SmithBothaViglietti2022" />

The types and diversity of ichnofossils in a locality has been used as an indicator measuring aridity. Nurra, an ichnofossil site on the island of [[Sardinia]], shows evidence of major drought-related stress among crustaceans. Whereas the Permian subnetwork at Nurra displays extensive horizontal backfilled traces and high ichnodiversity, the Early Triassic subnetwork is characterised by an absence of backfilled traces, an ichnological sign of aridification.<ref>{{cite journal |last1=Baucon |first1=Andrea |last2=Ronchi |first2=Ausonio |last3=Felletti |first3=Fabrizio |last4=Neto de Carvalho |first4=Carlos |date=15 September 2014 |title=Evolution of Crustaceans at the edge of the end-Permian crisis: Ichnonetwork analysis of the fluvial succession of Nurra (Permian–Triassic, Sardinia, Italy) |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018214002909 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=410 |pages=74–103 |doi=10.1016/j.palaeo.2014.05.034 |bibcode=2014PPP...410...74B |access-date=8 April 2023|url-access=subscription }}</ref>

=== Ozone depletion ===
A collapse of the atmospheric ozone shield has been invoked as an explanation for the mass extinction,<ref>{{Cite journal |last1=Black |first1=Benjamin A. |last2=Lamarque |first2=Jean-François |last3=Shields |first3=Christine A. |last4=Elkins-Tanton |first4=Linda T. |last5=Kiehl |first5=Jeffrey T. |date=1 January 2014 |title=Acid rain and ozone depletion from pulsed Siberian Traps magmatism |url=http://pubs.geoscienceworld.org/geology/article/42/1/67/131353/Acid-rain-and-ozone-depletion-from-pulsed-Siberian |journal=[[Geology (journal)|Geology]] |language=en |volume=42 |issue=1 |pages=67–70 |doi=10.1130/G34875.1 |bibcode=2014Geo....42...67B |issn=1943-2682 |access-date=18 June 2024 |via=GeoScienceWorld|url-access=subscription }}</ref><ref>{{cite journal |last1=Van de Schootbrugge |first1=Bas |last2=Wignall |first2=Paul Barry |date=26 October 2015 |title=A tale of two extinctions: converging end-Permian and end-Triassic scenarios |url=https://pubs.geoscienceworld.org/geolmag/article-abstract/153/2/332/251216/A-tale-of-two-extinctions-converging-end-Permian?redirectedFrom=fulltext |journal=[[Geological Magazine]] |volume=153 |issue=2 |pages=332–354 |doi=10.1017/S0016756815000643 |hdl=1874/329922 |s2cid=131750128 |access-date=26 May 2023|hdl-access=free }}</ref> particularly that of terrestrial plants.<ref name="BencaDuijnsteeLooy2018">{{cite journal |last1=Benca |first1=Jeffrey P. |last2=Duijnstee |first2=Ivo A. P. |last3=Looy |first3=Cindy V. |date=7 February 2018 |title=UV-B–induced forest sterility: Implications of ozone shield failure in Earth's largest extinction |journal=[[Science Advances]] |volume=4 |issue=2 |pages=e1700618 |doi=10.1126/sciadv.1700618 |pmid=29441357 |pmc=5810612 |bibcode=2018SciA....4..618B }}</ref> Ozone production may have been reduced by 60–70%, increasing the flux of ultraviolet radiation by 400% at equatorial latitudes and 5,000% at polar latitudes.<ref>{{cite journal |last1=Benton |first1=Michael James |date=3 September 2018 |title=Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction |journal=[[Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences]] |volume=376 |issue=2130 |pages=1–19 |doi=10.1098/rsta.2017.0076 |pmid=30177561 |pmc=6127390 |bibcode=2018RSPTA.37670076B }}</ref> The hypothesis has the advantage of explaining the mass extinction of plants, which would have added to the methane levels and should otherwise have thrived in an atmosphere with a high level of carbon dioxide. Fossil spores from the end-Permian further support the theory; many spores show deformities that could have been caused by [[ultraviolet radiation]], which would have been more intense after hydrogen sulfide emissions weakened the ozone layer.<ref name="FosterAndAfonin2005">{{cite journal |last1=Foster |first1=C. B. |last2=Afonin |first2=S. A. |date=July 2005 |title=Abnormal pollen grains: an outcome of deteriorating atmospheric conditions around the Permian–Triassic boundary |url=https://www.lyellcollection.org/doi/10.1144/0016-764904-047 |journal=[[Journal of the Geological Society]] |volume=162 |issue=4 |pages=653–659 |doi=10.1144/0016-764904-047 |bibcode=2005JGSoc.162..653F |s2cid=128829042 |access-date=26 May 2023|url-access=subscription }}</ref><ref name="EnvironmentalMutagenesis" /> Malformed plant spores from the time of the extinction event show an increase in ultraviolet B absorbing compounds, confirming that increased ultraviolet radiation played a role in the environmental catastrophe and excluding other possible causes of mutagenesis, such as heavy metal toxicity, in these mutated spores.<ref name="DyingInTheSun">{{cite journal |last1=Liu |first1=Feng |last2=Peng |first2=Huiping |last3=Marshall |first3=John E. A. |last4=Lomax |first4=Barry H. |last5=Bomfleur |first5=Benjamin |last6=Kent |first6=Matthew S. |last7=Fraser |first7=Wesley T. |last8=Jardine |first8=Phillip E. |date=6 January 2023 |title=Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction |journal=[[Science Advances]] |volume=9 |issue=1 |pages=eabo6102 |doi=10.1126/sciadv.abo6102 |pmid=36608140 |pmc=9821938 |bibcode=2023SciA....9O6102L }}</ref> Extremely positive Δ<sup>33</sup>S anomalies provide evidence of photolysis of volcanic SO<sub>2</sub>, indicating increased ultraviolet radiation flux.<ref>{{Cite journal |last1=Li |first1=Rucao |last2=Shen |first2=Shu-Zhong |last3=Xia |first3=Xiao-Ping |last4=Xiao |first4=Bing |last5=Feng |first5=Yuzhou |last6=Chen |first6=Huayong |date=5 March 2024 |title=Atmospheric ozone destruction and the end-Permian crisis: Evidence from multiple sulfur isotopes |url=https://linkinghub.elsevier.com/retrieve/pii/S0009254124000160 |journal=[[Chemical Geology]] |language=en |volume=647 |pages=121936 |doi=10.1016/j.chemgeo.2024.121936 |access-date=21 May 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Sulphur isotope data from North China are inconsistent with a total collapse of the ozone layer, however, suggesting it may have not been as major a kill mechanism as others.<ref>{{Cite journal |last1=Dal Corso |first1=Jacopo |last2=Newton |first2=Robert J. |last3=Zerkle |first3=Aubrey L. |last4=Chu |first4=Daoliang |last5=Song |first5=Haijun |last6=Song |first6=Huyue |last7=Tian |first7=Li |last8=Tong |first8=Jinnan |last9=Di Rocco |first9=Tommaso |last10=Claire |first10=Mark W. |last11=Mather |first11=Tamsin A. |last12=He |first12=Tianchen |last13=Gallagher |first13=Timothy |last14=Shu |first14=Wenchao |last15=Wu |first15=Yuyang |last16=Bottrell |first16=Simon H. |last17=Metcalfe |first17=Ian |last18=Cope |first18=Helen A. |last19=Novak |first19=Martin |last20=Jamieson |first20=Robert A. |last21=Wignall |first21=Paul Barry |date=2 September 2024 |title=Repeated pulses of volcanism drove the end-Permian terrestrial crisis in northwest China |journal=[[Nature Communications]] |language=en |volume=15 |issue=1 |pages=7628 |doi=10.1038/s41467-024-51671-5 |pmid=39223125 |issn=2041-1723 |pmc=11368959 |bibcode=2024NatCo..15.7628D }}</ref>

Multiple mechanisms could have reduced the ozone shield and rendered it ineffective. Computer modelling shows high atmospheric methane levels are associated with ozone shield decline and may have contributed to its reduction during the PTME.<ref>{{cite journal |last1=Lamarque |first1=J.-F. |last2=Kiehl |first2=J. T. |last3=Shields |first3=C. A. |last4=Boville |first4=B. A. |last5=Kinnison |first5=D. E. |date=9 August 2006 |title=Modeling the response to changes in tropospheric methane concentration: Application to the Permian-Triassic boundary |journal=[[Paleoceanography and Paleoclimatology]] |volume=21 |issue=3 |pages=1–15 |doi=10.1029/2006PA001276 |bibcode=2006PalOc..21.3006L |doi-access=free }}</ref> Volcanic emissions of sulphate aerosols into the stratosphere would have dealt significant destruction to the ozone layer.<ref name="FosterAndAfonin2005" /> As mentioned previously, the rocks in the region where the Siberian Traps were emplaced are extremely rich in halogens.<ref name="BroadleyEtAl2018" /> The intrusion of Siberian Traps volcanism into deposits rich in organohalogens, such as [[methyl bromide]] and [[methyl chloride]], would have been another source of ozone destruction.<ref>{{Cite journal |last1=Beerling |first1=David J |last2=Harfoot |first2=Michael |last3=Lomax |first3=Barry |last4=Pyle |first4=John A |date=15 July 2007 |title=The stability of the stratospheric ozone layer during the end-Permian eruption of the Siberian Traps |url=https://royalsocietypublishing.org/doi/10.1098/rsta.2007.2046 |journal=[[Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences]] |language=en |volume=365 |issue=1856 |pages=1843–1866 |doi=10.1098/rsta.2007.2046 |pmid=17513258 |bibcode=2007RSPTA.365.1843B |issn=1364-503X |access-date=18 June 2024|url-access=subscription }}</ref><ref name="EnvironmentalMutagenesis" /> An uptick in wildfires, a natural source of methyl chloride, would have had further deleterious effects still on the atmospheric ozone shield.<ref>{{cite journal |last1=Black |first1=Benjamin A. |last2=Lamarque |first2=Jean-François |last3=Shields |first3=Christine A. |last4=Elkins-Tanton |first4=Linda T. |last5=Kiehl |first5=Jeffrey T. |date=1 January 2014 |title=Acid rain and ozone depletion from pulsed Siberian Traps magmatism |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/42/1/67/131353/Acid-rain-and-ozone-depletion-from-pulsed-Siberian |journal=[[Geology (journal)|Geology]] |volume=42 |issue=1 |pages=67–70 |doi=10.1130/G34875.1 |bibcode=2014Geo....42...67B |access-date=31 May 2023|url-access=subscription }}</ref> Upwelling of euxinic water may have released massive [[hydrogen sulphide]] emissions into the atmosphere and would poison terrestrial plants and animals and severely weaken the [[ozone layer]], exposing much of the life that remained to fatal levels of [[UV radiation]],<ref>{{cite journal |last1=Lamarque |first1=J.-F. |last2=Kiehl |first2=J. T. |last3=Orlando |first3=J. J. |date=16 January 2007 |title=Role of hydrogen sulfide in a Permian-Triassic boundary ozone collapse |journal=[[Geophysical Research Letters]] |volume=34 |issue=2 |pages=1–4 |doi=10.1029/2006GL028384 |bibcode=2007GeoRL..34.2801L |s2cid=55812439 |doi-access=free }}</ref> although other modelling work has found that the release of this gas would not have significantly damaged the ozone layer.<ref>{{Cite journal |last1=Kaiho |first1=Kunio |last2=Koga |first2=Seizi |date=August 2013 |title=Impacts of a massive release of methane and hydrogen sulfide on oxygen and ozone during the late Permian mass extinction |url=https://linkinghub.elsevier.com/retrieve/pii/S0921818113000945 |journal=[[Global and Planetary Change]] |language=en |volume=107 |pages=91–101 |doi=10.1016/j.gloplacha.2013.04.004 |bibcode=2013GPC...107...91K |access-date=18 June 2024 |via=Elsevier Science Direct|url-access=subscription }}</ref> Indeed, [[Biosignature|biomarker]] evidence for anaerobic photosynthesis by [[Chlorobiaceae]] (green sulfur bacteria) from the Late-Permian into the Early Triassic indicates that hydrogen sulphide did upwell into shallow waters because these bacteria are restricted to the photic zone and use sulfide as an [[electron donor]].<ref name=Kump2005>{{cite journal |last1=Kump |first1=Lee |last2=Pavlov |first2=Alexander |first3=Michael A. |last3=Arthur |title=Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia |journal=[[Geology (journal)|Geology]] |date=1 May 2005 |volume=33 |issue=5 |pages=397–400 |url=https://www.researchgate.net/publication/253144294 |doi=10.1130/G21295.1 |bibcode=2005Geo....33..397K |access-date=2 April 2023}}</ref>

=== Asteroid impact ===
[[File:Impact event.jpg|thumb|left|Artist's impression of a major impact event: A collision between Earth and an [[asteroid]] a few kilometers in diameter would release as much energy as the detonation of several million nuclear weapons.]]
Evidence that an [[impact event]] may have caused the [[Cretaceous–Paleogene extinction]] has led to speculation that similar impacts may have been the cause of other extinction events, including the P–Tr extinction, and thus to a search for evidence of impacts at the times of other extinctions, such as large [[impact craters]] of the appropriate age.<ref name="UnderAGreenSky">{{cite book |last1=Ward |first1=Peter Douglas |date=17 April 2007 |title=Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future |chapter=The Mother of All Extinctions |location=New York |publisher=HarperCollins |pages=61–86 |isbn=978-0-06-113791-4}}</ref> However, suggestions that an asteroid impact was the trigger of the Permian-Triassic extinction are now largely rejected.<ref>{{Cite journal |last1=Algeo |first1=Thomas J |last2=Shen |first2=Jun |date=8 September 2023 |title=Theory and classification of mass extinction causation |journal=National Science Review |volume=11 |issue=1 |pages=nwad237 |language=en |doi=10.1093/nsr/nwad237 |issn=2095-5138|doi-access=free |pmid=38116094 |pmc=10727847 }}</ref><ref name=":1" />

Reported evidence for an impact event from the P–Tr boundary level includes rare grains of [[shocked quartz]] in Australia and Antarctica;<ref name="Retallack_etal_1998">{{cite journal |vauthors=Retallack GJ, Seyedolali A, Krull ES, Holser WT, Ambers CP, Kyte FT | title=Search for evidence of impact at the Permian–Triassic boundary in Antarctica and Australia | journal=[[Geology (journal)|Geology]] | volume=26 | issue=11 | year=1998 | pages=979–982 | doi=10.1130/0091-7613(1998)026<0979:SFEOIA>2.3.CO;2
|bibcode = 1998Geo....26..979R }}
<br /></ref><ref name="becker_etal_2004">{{cite journal |vauthors=Becker L, Poreda RJ, Basu AR, Pope KO, Harrison TM, Nicholson C, Iasky R | title=Bedout: a possible end-Permian impact crater offshore of northwestern Australia | journal=[[Science (journal)|Science]] | volume=304 | issue=5676 | year=2004 | pages=1469–1476 |doi=10.1126/science.1093925 | pmid=15143216
|bibcode = 2004Sci...304.1469B | s2cid=17927307 }}</ref> [[fullerenes]] trapping extraterrestrial noble gases;<ref name="becker_etal_2001">{{cite journal |vauthors=Becker L, Poreda RJ, Hunt AG, Bunch TE, Rampino M | title=Impact event at the Permian–Triassic boundary: Evidence from extraterrestrial noble gases in fullerenes | journal=[[Science (journal)|Science]] | volume=291 | issue=5508 | year=2001 | pages=1530–1533 | doi=10.1126/science.1057243 | pmid=11222855
|bibcode = 2001Sci...291.1530B | s2cid=45230096 }}</ref> meteorite fragments in Antarctica;<ref name="basu_etal_2003">{{cite journal |vauthors=Basu AR, Petaev MI, Poreda RJ, Jacobsen SB, Becker L | title=Chondritic meteorite fragments associated with the Permian–Triassic boundary in Antarctica | journal=[[Science (journal)|Science]] | volume=302 | issue=5649 | year=2003 | pages=1388–1392 |doi=10.1126/science.1090852 | pmid=14631038
|bibcode = 2003Sci...302.1388B | s2cid=15912467 }}</ref> and grains rich in iron, nickel, and silicon, which may have been created by an impact.<ref name="Kaiho_etal_2001">{{cite journal |vauthors=Kaiho K, Kajiwara Y, Nakano T, Miura Y, Kawahata H, Tazaki K, Ueshima M, Chen Z, Shi GR | title=End-Permian catastrophe by a bolide impact: Evidence of a gigantic release of sulfur from the mantle | journal=[[Geology (journal)|Geology]] | volume=29 | issue=9 | year=2001 | pages=815–818 | doi=10.1130/0091-7613(2001)029<0815:EPCBAB>2.0.CO;2 | issn=0091-7613
|bibcode = 2001Geo....29..815K }}</ref> However, the accuracy of most of these claims has been challenged.<ref name="Farley_etal_2001">{{cite journal |vauthors=Farley KA, Mukhopadhyay S, Isozaki Y, Becker L, Poreda RJ | title=An extraterrestrial impact at the Permian–Triassic boundary? | journal=[[Science (journal)|Science]] | volume=293 | issue=5539 | year=2001 | pages=2343a–2343 | doi=10.1126/science.293.5539.2343a | pmid=11577203
|doi-access= }}</ref><ref name="Koeberl_etal_2002">{{cite journal |vauthors=Koeberl C, Gilmour I, Reimold WU, Philippe Claeys P, Ivanov B | title=End-Permian catastrophe by bolide impact: Evidence of a gigantic release of sulfur from the mantle: Comment and Reply | journal=[[Geology (journal)|Geology]] | volume=30 | issue=9 | year=2002 | pages=855–856|doi=10.1130/0091-7613(2002)030<0855:EPCBBI>2.0.CO;2 | issn=0091-7613
|bibcode = 2002Geo....30..855K }}</ref><ref name="Isbell_etal_1999">{{cite journal |vauthors=Isbell JL, Askin RA, Retallack GR | title=Search for evidence of impact at the Permian–Triassic boundary in Antarctica and Australia; discussion and reply | journal=[[Geology (journal)|Geology]] | volume=27 | issue=9 | year=1999 | pages=859–860|doi=10.1130/0091-7613(1999)027<0859:SFEOIA>2.3.CO;2
|bibcode = 1999Geo....27..859I }}</ref><ref name="Koeberl_etal_2004">{{cite journal |vauthors=Koeberl K, Farley KA, Peucker-Ehrenbrink B, Sephton MA | title=Geochemistry of the end-Permian extinction event in Austria and Italy: No evidence for an extraterrestrial component | journal=[[Geology (journal)|Geology]] | volume=32 | issue=12 | year=2004 | pages=1053–1056 |doi=10.1130/G20907.1
|bibcode = 2004Geo....32.1053K }}</ref> For example, quartz from [[Graphite Peak]] in Antarctica, once considered "shocked", has been re-examined by optical and transmission electron microscopy. The observed features were concluded to be due not to shock, but rather to [[plastic deformation]], consistent with formation in a [[tectonics|tectonic]] environment such as [[volcanism]].<ref name="Langanhorst_etal_2005">{{cite conference |vauthors=Langenhorst F, Kyte FT, Retallack GJ | title=Reexamination of quartz grains from the Permian–Triassic boundary section at Graphite Peak, Antarctica | book-title=Lunar and Planetary Science Conference XXXVI |year=2005 |url=http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2358.pdf|access-date=2007-07-13
}}</ref> Iridium levels in many sites straddling the Permian-Triassic boundaries are not anomalous, providing evidence against an extraterrestrial impact as the PTME's cause.<ref>{{cite journal |last1=Zhou |first1=Lei |last2=Kyte |first2=Frank T. |date=25 November 1988 |title=The Permian-Triassic boundary event: a geochemical study of three Chinese sections |url=https://www.sciencedirect.com/science/article/abs/pii/0012821X88901392 |journal=[[Earth and Planetary Science Letters]] |volume=90 |issue=4 |pages=411–421 |doi=10.1016/0012-821X(88)90139-2 |bibcode=1988E&PSL..90..411L |access-date=31 May 2023|url-access=subscription }}</ref>

An impact crater on the seafloor would be evidence of a possible cause of the P–Tr extinction, but such a crater would by now have disappeared. As 70% of the Earth's surface is currently sea, an [[asteroid]] or [[comet]] fragment is now perhaps more than twice as likely to hit the ocean as it is to hit land. However, Earth's oldest ocean-floor crust is only 200&nbsp;million years old as it is continually being destroyed and renewed by spreading and [[subduction]]. Furthermore, craters produced by very large impacts may be masked by extensive [[flood basalt]]ing from below after the crust is punctured or weakened.<ref name="Jones_etal_2002">{{cite journal |vauthors=Jones AP, Price GD, Price NJ, DeCarli PS, Clegg RA | title=Impact induced melting and the development of large igneous provinces | journal=[[Earth and Planetary Science Letters]] | volume=202 | issue=3 | year=2002 | pages=551–561 |doi=10.1016/S0012-821X(02)00824-5 | bibcode=2002E&PSL.202..551J
| citeseerx=10.1.1.469.3056 }}</ref> Yet, subduction should not be entirely accepted as an explanation for the lack of evidence: as with the K-T event, an ejecta blanket stratum rich in [[Siderophile element|siderophilic elements]] (such as [[iridium]]) would be expected in formations from the time.

A large impact might have triggered other mechanisms of extinction described above,<ref name="White" /> such as the Siberian Traps eruptions at either an impact site<ref name="Hager, Bradford H, 2001; Elkins Tanton, Linda T">{{cite conference | author=AHager, Bradford H. | title=Giant Impact Craters Lead To Flood Basalts: A Viable Model | book-title=CCNet 33/2001: Abstract 50470 | year=2001 | url=http://abob.libs.uga.edu/bobk/ccc/cc030101.html | access-date=2008-04-06 | archive-date=2008-04-22 | archive-url=https://web.archive.org/web/20080422015709/http://abob.libs.uga.edu/bobk/ccc/cc030101.html | url-status=dead }}</ref> or the [[Antipodes|antipode]] of an impact site.<ref name="White" /><ref name="Hagstrum, Jonathan T, 2001">{{cite conference | author=Hagstrum, Jonathan T. | title=Large Oceanic Impacts As The Cause Of Antipodal Hotspots And Global Mass Extinctions | book-title=CCNet 33/2001: Abstract 50288 | year=2001 | url=http://abob.libs.uga.edu/bobk/ccc/cc030101.html | access-date=2008-04-06 | archive-date=2008-04-22 | archive-url=https://web.archive.org/web/20080422015709/http://abob.libs.uga.edu/bobk/ccc/cc030101.html | url-status=dead }}</ref> The abruptness of an impact also explains why more species did not [[Rapid modes of evolution|rapidly evolve]] to survive, as would be expected if the Permian–Triassic event had been slower and less global than a meteorite impact.

Bolide impact claims have been criticised on the grounds that they are unnecessary as explanations for the extinctions, and they do not fit the known data compatible with a protracted extinction spanning thousands of years.<ref>{{cite journal |last1=Romano |first1=Marco |last2=Bernardi |first2=Massimo |last3=Petti |first3=Fabio Massimo |last4=Rubidge |first4=Bruce |last5=Hancox |first5=John |last6=Benton |first6=Michael James |date=November 2020 |title=Early Triassic terrestrial tetrapod fauna: a review |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825220303779 |journal=[[Earth-Science Reviews]] |volume=210 |page=103331 |doi=10.1016/j.earscirev.2020.103331 |bibcode=2020ESRv..21003331R |s2cid=225066013 |access-date=4 January 2023|url-access=subscription }}</ref> Additionally, many sites spanning the Permian-Triassic boundary display a complete lack of evidence of an impact event.<ref>{{cite journal |last1=Burger |first1=Benjamin J. |last2=Vargas Estrada |first2=Margarita |last3=Gustin |first3=Mae Sexauer |date=June 2019 |title=What caused Earth's largest mass extinction event? New evidence from the Permian-Triassic boundary in northeastern Utah |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818118301322 |journal=[[Global and Planetary Change]] |volume=177 |pages=81–100 |doi=10.1016/j.gloplacha.2019.03.013 |bibcode=2019GPC...177...81B |s2cid=134324242 |access-date=2 April 2023}}</ref>

==== Possible impact sites ====
Possible impact craters proposed as the site of an impact causing the P–Tr extinction include the {{convert|250|km|mi|abbr=on}} [[Bedout]] structure off the northwest coast of Australia<ref name="becker_etal_2004" /> and the hypothesized {{convert|480|km|mi|abbr=on}} [[Wilkes Land crater]] of East Antarctica.<ref name="vfp06">{{cite journal |last1=Frese |first1=Ralph R. B. von |author-link1=Ralph von Frese |last2=Potts |first2=Laramie V. |author-link2=Laramie Potts |last3=Wells |first3=Stuart B. |last4=Gaya-Piqué |first4=Luis-Ricardo |last5=Golynsky |first5=Alexander V. |last6=Hernandez |first6=Orlando |last7=Kim |first7=Jeong Woo |last8=Kim |first8=Hyung Rae |last9=Hwang |first9=Jong Sun |title=Permian–Triassic mascon in Antarctica |journal=American Geophysical Union, Fall Meeting 2007 |date=2006 |volume=2007 |pages=Abstract T41A–08 |bibcode=2006AGUSM.T41A..08V |url=https://www.researchgate.net/publication/241531088 }}</ref><ref name="vf09">{{cite journal |last1=Frese |first1=Ralph R. B. von |author-link1=Ralph von Frese |last2=Potts |first2=Laramie V. |author-link2=Laramie Potts |last3=Wells |first3=Stuart B. |last4=Leftwich |first4=Timothy E. |last5=Kim |first5=Hyung Rae |last6=Kim |first6=Jeong Woo |last7=Golynsky |first7=Alexander V. |last8=Hernandez |first8=Orlando |last9=Gaya-Piqué |first9=Luis-Ricardo |title=GRACE gravity evidence for an impact basin in Wilkes Land, Antarctica |journal=[[Geochemistry, Geophysics, Geosystems]] |volume=10 |number=2 |date=25 February 2009 |doi=10.1029/2008GC002149 |bibcode=2009GGG....10.2014V |issn=1525-2027 |url=https://www.researchgate.net/publication/241531088 |doi-access=free }}</ref> An impact has not been proved in either case, and the idea has been widely criticized. The Wilkes Land geophysical feature is of very uncertain age, possibly later than the Permian–Triassic extinction.

Another impact hypothesis postulates that the impact event that formed the [[Araguainha crater]], whose formation has been dated to {{nowrap|254.7 ± 2.5 million}}, a possible temporal range overlapping with the end-Permian extinction,<ref name="Tohver2012">{{cite journal |title=Geochronological constraints on the age of a Permo–Triassic impact event: U–Pb and {{sup|40}}Ar ''/'' {{sup|39}}Ar results for the 40&nbsp;km Araguainha structure of central Brazil |author1=Tohver, Eric |author2=Lana, Cris |author3=Cawood, P.A. |author4=Fletcher, I.R. |author5=Jourdan, F. |author6=Sherlock, S. |author7=Rasmussen, B. |author8=Trindade, R.I.F. |author9=Yokoyama, E. |author10=Souza Filho, C.R. |author11=Marangoni, Y. |display-authors=6 |journal=[[Geochimica et Cosmochimica Acta]] |volume=86 |date=1 June 2012 |pages=214–227 |doi=10.1016/j.gca.2012.03.005 |bibcode=2012GeCoA..86..214T}}</ref> precipitated the mass extinction.<ref name="UWAPressRelease">{{cite press release |title=Biggest extinction in history caused by climate-changing meteor |publisher=University of Western Australia |newspaper=University News |date=31 July 2013 |url=http://www.news.uwa.edu.au/201307315921/international/biggest-extinction-history-caused-climate-changing-meteor}}</ref> The impact occurred around extensive deposits of oil shale in the shallow marine Paraná–Karoo Basin, whose perturbation by the seismicity resulting from impact likely discharged about 1.6 teratonnes of methane into Earth's atmosphere, buttressing the already rapid warming caused by hydrocarbon release due to the Siberian Traps.<ref name="Tohver2013">{{cite journal |last1=Tohver |first1=Eric |last2=Cawood |first2=P. A. |last3=Riccomini |first3=Claudio |last4=Lana |first4=Cris |last5=Trindade |first5=R. I. F. |date=1 October 2013 |title=Shaking a methane fizz: Seismicity from the Araguainha impact event and the Permian–Triassic global carbon isotope record |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018213003313 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=387 |pages=66–75 |doi=10.1016/j.palaeo.2013.07.010 |bibcode=2013PPP...387...66T |access-date=2024-03-26}}</ref> The large earthquakes generated by the impact would have additionally generated massive tsunamis across much of the globe.<ref name="UWAPressRelease" /><ref name="Tohver2018">{{cite journal |last1=Tohver |first1=Eric |last2=Schmieder |first2=Martin |last3=Lana |first3=Cris |last4=Mendes |first4=Pedro S. T. |last5=Jourdan |first5=Fred |last6=Warren |first6=Lucas |last7=Riccomini |first7=Claudio |date=2 January 2018 |title=End-Permian impactogenic earthquake and tsunami deposits in the intracratonic Paraná Basin of Brazil |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article/130/7-8/1099/525698/End-Permian-impactogenic-earthquake-and-tsunami |journal=[[Geological Society of America Bulletin]] |volume=130 |issue=7–8 |pages=1099–1120 |doi=10.1130/B31626.1 |bibcode=2018GSAB..130.1099T |access-date=2024-03-26|url-access=subscription }}</ref> Despite this, most palaeontologists reject the impact as being a significant driver of the extinction, citing the relatively low energy (equivalent to 10<sup>5</sup> to 10<sup>6</sup> of TNT, around two orders of magnitude lower than the impact energy believed to be required to induce mass extinctions) released by the impact.<ref name="Tohver2013" />

A 2017 paper noted the discovery of a circular gravity anomaly near the [[Falkland Islands]] that might correspond to an impact crater with a diameter of {{convert|250|km|mi|abbr=on}},<ref name="rocca">{{cite journal |author1=Rocca, M. |author2=Rampino, M. |author3=Baez Presser, J. |year=2017 |title=Geophysical evidence for a la impact structure on the Falkland (Malvinas) Plateau|journal=[[Terra Nova (journal)|Terra Nova]] |volume=29 |issue=4 |pages=233–237 |bibcode=2017TeNov..29..233R |doi=10.1111/ter.12269 |s2cid=134484465 }}</ref> as supported by seismic and magnetic evidence. Estimates for the age of the structure range up to 250&nbsp;million years old. This would be substantially larger than the well-known {{convert|180|km|mi|abbr=on}} [[Chicxulub crater|Chicxulub impact crater]] associated with a later extinction. However, Dave McCarthy and colleagues from the British Geological Survey illustrated that the gravity anomaly is not circular and also that the seismic data presented by Rocca, Rampino and Baez Presser did not cross the proposed crater or provide any evidence for an impact crater.<ref>{{Cite journal |last1=McCarthy |first1=Dave |last2=Aldiss |first2=Don |last3=Arsenikos |first3=Stavros |last4=Stone |first4=Phil |last5=Richards |first5=Phil |date=24 August 2017 |title=Comment on "Geophysical evidence for a large impact structure on the Falkland (Malvinas) Plateau" |journal=[[Terra Nova (journal)|Terra Nova]] |language=en |volume=29 |issue=6 |pages=411–415 |doi=10.1111/ter.12285 |issn=0954-4879 |bibcode=2017TeNov..29..411M |s2cid=133781924 |url=http://nora.nerc.ac.uk/id/eprint/525290/1/McCarthy%20et%20al%20Terra_Nova%202017.pdf |access-date=26 March 2023}}</ref>

=== Methanogens ===
A hypothesis published in 2014 posits that a genus of [[Anaerobic respiration|anaerobic]] methanogenic [[archaea]] known as ''[[Methanosarcina]]'' was responsible for the event. Three lines of evidence suggest that these microbes acquired a new metabolic pathway via [[gene transfer]] at about that time, enabling them to efficiently metabolize acetate into methane. That would have led to their exponential reproduction, allowing them to rapidly consume vast deposits of organic carbon that had accumulated in marine sediment. The result would have been a sharp buildup of methane and carbon dioxide in the oceans and atmosphere, in a manner that may be consistent with the <sup>13</sup>C/<sup>12</sup>C isotopic record. Massive volcanism facilitated this process by releasing large amounts of [[nickel]], a scarce metal that is a cofactor for enzymes involved in producing methane.<ref name="Rothman2014">{{Cite journal | doi = 10.1073/pnas.1318106111| title = Methanogenic burst in the end-Permian carbon cycle| journal = [[Proceedings of the National Academy of Sciences of the United States of America]]| date = 31 March 2014 | last1 = Rothman | first1 = D.H.| last2 = Fournier | first2 = G.P.| last3 = French | first3 = K.L.| last4 = Alm | first4 = E.J.| last5 = Boyle | first5 = E.A.| last6 = Cao | first6 = C.| last7 = Summons | first7 = R.E.| pmid = 24706773 | pmc=3992638 | volume=111 | issue=15 | pages=5462–5467| bibcode = 2014PNAS..111.5462R| doi-access = free}} – Lay summary: {{cite web | url=https://www.sciencedaily.com/releases/2014/03/140331153608.htm | title=Ancient whodunit may be solved: Methane-producing microbes did it! | first=David L. | last=Chandler | website=Science Daily | date=March 31, 2014}}</ref> Chemostratigraphic analysis of Permian-Triassic boundary sediments in Chaotian demonstrates a methanogenic burst could be responsible for some percentage of the carbon isotopic fluctuations.<ref name="SaitohIsozaki2021">{{cite journal |last1=Saitoh |first1=Masafumi |last2=Isozaki |first2=Yukio |date=5 February 2021 |title=Carbon Isotope Chemostratigraphy Across the Permian-Triassic Boundary at Chaotian, China: Implications for the Global Methane Cycle in the Aftermath of the Extinction |journal=[[Frontiers in Earth Science]] |volume=8 |page=665 |doi=10.3389/feart.2020.596178 |bibcode=2021FrEaS...8..665S |doi-access=free }}</ref> On the other hand, in the canonical Meishan sections, the nickel concentration increases somewhat after the {{delta|13|C|}} concentrations have begun to fall.<ref>{{cite journal |doi=10.1093/nsr/nwu047 |title=The end-Permian mass extinction: A still unexplained catastrophe |journal=[[National Science Review]] |volume=1 |issue=4 |pages=492–495 |year=2014 |last1=Shen |first1=Shu-Zhong |last2=Bowring |first2=Samuel A. |doi-access=free}}</ref>

=== Interstellar dust ===
[[John Gribbin]] argues that the [[Solar System]] last passed through a [[spiral arm]] of the [[Milky Way]] around 250&nbsp;million years ago and that the resultant [[interstellar dust|dusty gas clouds]] may have caused a dimming of the Sun, which combined with the effect of Pangaea to produce an ice age.<ref>{{cite book |last=Gribbin |first=John |author-link=John Gribbin |title=Alone in the Universe: Why our Planet is Unique |pages=72–73 |publisher=John Wiley & Sons |location=Hoboken, NJ |year=2012 |isbn=978-1-118-14797-9}}</ref>