Editing Permian–Triassic extinction event (section)

=== 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>