Editing Extinction event (section)

===Most widely supported explanations===
MacLeod (2001)<ref>{{cite web | vauthors = MacLeod N | date=2001-01-06 | title=Extinction! | website=firstscience.com | url=http://www.firstscience.com/SITE/ARTICLES/macleod.asp}}</ref> summarized the relationship between mass extinctions and events that are most often cited as causes of mass extinctions, using data from Courtillot, Jaeger & Yang ''et al.'' (1996),<ref>{{cite book | vauthors = Courtillot V, Jaeger JJ, Yang Z, Feraud G, Hofmann C | year = 1996 | chapter = The influence of continental flood basalts on mass extinctions: Where do we stand? | title = The Cretaceous-Tertiary Event and other Catastrophes in Earth History | isbn = 9780813723075 | doi = 10.1130/0-8137-2307-8.513 }}</ref> Hallam (1992)<ref>{{cite book | vauthors = Hallam A | author-link = Anthony Hallam | year = 1992 | title = Phanerozoic sea-level changes | location = New York, NY | publisher = Columbia University Press | isbn = 978-0-231-07424-7 }}</ref> and Grieve & Pesonen (1992):<ref>{{cite journal | vauthors = Grieve RA, Pesonen LJ | date = December 1992 | title = The Terrestrial Impact Cratering Record | journal = Tectonophysics | volume = 216 | issue = 1–2 | pages = 1–30 | doi = 10.1016/0040-1951(92)90152-V | bibcode = 1992Tectp.216....1G }}</ref>
* [[Flood basalt]] events (giant volcanic eruptions): 11&nbsp;occurrences, all associated with significant extinctions.{{efn| name=i|The earliest known flood basalt event is the one that produced the [[Siberian Traps]] and is associated with the [[Permian–Triassic extinction event|end-Permian extinction]].}}{{efn|name=ii|
Some of the extinctions associated with flood basalts and sea-level falls were significantly smaller than the "major" extinctions, but still much greater than the background extinction level.}} But Wignall (2001) concluded that only five of the major extinctions coincided with flood basalt eruptions and that the main phase of extinctions started before the eruptions.<ref>{{cite journal | vauthors = Wignall PB | year = 2001 | title = Large igneous provinces and mass extinctions | journal = Earth-Science Reviews | volume = 53 | issue = 1–2 | pages = 1–33 | doi = 10.1016/S0012-8252(00)00037-4 | bibcode = 2001ESRv...53....1W }}</ref>
* Sea-level falls: 12, of which seven were associated with significant extinctions.{{efn|name=ii}}
* [[Impact event|Asteroid impacts]]: one large impact is associated with a mass extinction, that is, the Cretaceous–Paleogene extinction event; there have been many smaller impacts but they are not associated with significant extinctions,<ref>{{cite book | vauthors = Brannen P | year = 2017 | title = The Ends of the World: Volcanic Apocalypses, Lethal Oceans, and Our Quest to Understand Earth's Past Mass Extinctions | publisher = Harper Collins | page = 336 | isbn = 978-0-06-236480-7 }}</ref> or cannot be dated precisely enough. The impact that created the [[Siljan Ring]] either was just before the Late Devonian Extinction or coincided with it.<ref>{{cite conference | vauthors = Morrow JR, Sandberg CA | url =  http://www.lpi.usra.edu/meetings/metsoc2005/pdf/5148.pdf | title = Revised Dating Of Alamo And Some Other Late Devonian Impacts In Relation To Resulting Mass Extinction | conference = 68th Annual Meteoritical Society Meeting | date = 2005 }}</ref>

The most commonly suggested causes of mass extinctions are listed below.

====Flood basalt events====
[[File:Extent of Siberian traps german.png|thumb|right|240px|The scientific consensus is that the main cause of the End-Permian extinction event was the large amount of [[carbon dioxide]] emitted by the volcanic eruptions that created the [[Siberian Traps]], which elevated global temperatures.]]
The formation of [[large igneous province]]s by flood basalt events could have:
* produced dust and [[particulates|particulate]] aerosols, which inhibited photosynthesis and thus caused [[food chain]]s to collapse both on land and at sea<ref>{{cite magazine | vauthors = Courtillot VE |year=1990 |title=A volcanic eruption |magazine=[[Scientific American]] |volume=263 |issue=4 |pages=85–93 |pmid=11536474 |jstor=24997065 |doi=10.1038/scientificamerican1090-85 |bibcode=1990SciAm.263d..85C |url=https://www.scientificamerican.com/article/a-volcanic-eruption/ }}</ref>
* emitted sulfur oxides that were precipitated as [[acid rain]] and poisoned many organisms, contributing further to the collapse of food chains
* emitted [[carbon dioxide]] and thus possibly causing [[greenhouse effect|sustained global warming]] once the dust and particulate aerosols dissipated.
Flood basalt events occur as pulses of activity punctuated by dormant periods. As a result, they are likely to cause the climate to oscillate between cooling and warming, but with an overall trend towards warming as the carbon dioxide they emit can stay in the atmosphere for hundreds of years.

Flood basalt events have been implicated as the cause of many major extinction events.<ref>{{cite journal |last1=Rampino |first1=Michael R. |date=13 April 2010 |title=Mass extinctions of life and catastrophic flood basalt volcanism |journal= Proceedings of the National Academy of Sciences|volume=107 |issue=15 |pages=6555–6556 |doi=10.1073/pnas.1002478107 |pmid=20360556 |pmc=2872464 |bibcode=2010PNAS..107.6555R |doi-access=free }}</ref><ref>{{cite journal |last1=Bryan |first1=Scott E. |last2=Peate |first2=Ingrid Ukstins |last3=Peate |first3=David W. |last4=Self |first4=Stephen |last5=Jerram |first5=Dougal A. |last6=Mawby |first6=Michael R. |last7=Marsh |first7=J. S. (Goonie) |last8=Miller |first8=Jodie A. |date=October 2010 |title=The largest volcanic eruptions on Earth |url=https://www.sciencedirect.com/science/article/abs/pii/S0012825210000814 |journal=[[Earth-Science Reviews]] |volume=102 |issue=3–4 |pages=207–229 |doi=10.1016/j.earscirev.2010.07.001 |bibcode=2010ESRv..102..207B |access-date=11 January 2023}}</ref> It is speculated that massive volcanism caused or contributed to the [[Kellwasser event|Kellwasser Event]],<ref name=":1">{{cite journal |title=New <sup>40</sup>Ar/<sup>39</sup>Ar and K–Ar ages of the Viluy traps (Eastern Siberia): Further evidence for a relationship with the Frasnian–Famennian mass extinction |author=Ricci, J. |display-authors=etal |year=2013 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=386 |pages=531–540 |doi=10.1016/j.palaeo.2013.06.020|bibcode=2013PPP...386..531R }}</ref><ref name=B2014>{{cite journal |last1=Bond |first1=D. P. G. |last2=Wignall |first2=P. B. |year=2014 |title=Large igneous provinces and mass extinctions: An update |journal=GSA Special Papers |volume=505 |pages=29–55 |url=http://specialpapers.gsapubs.org/content/505/29.abstract |doi=10.1130/2014.2505(02) |isbn=9780813725055 |access-date=23 December 2022}}</ref><ref>{{cite journal |last1=Kaiho |first1=Kunio |last2=Miura |first2=Mami |last3=Tezuka |first3=Mio |last4=Hayashi |first4=Naohiro |last5=Jones |first5=David S. |last6=Oikawa |first6=Kazuma |last7=Casier |first7=Jean-Georges |last8=Fujibayashi |first8=Megumu |last9=Chen |first9=Zhong-Qiang |date=April 2021 |title=Coronene, mercury, and biomarker data support a link between extinction magnitude and volcanic intensity in the Late Devonian |url=https://www.sciencedirect.com/science/article/abs/pii/S0921818121000370 |journal=[[Global and Planetary Change]] |volume=199 |page=103452 |doi=10.1016/j.gloplacha.2021.103452 |bibcode=2021GPC...19903452K |s2cid=234364043 |access-date=11 January 2023|url-access=subscription }}</ref> the [[Capitanian mass extinction event|End-Guadalupian Extinction Event]],<ref name="JerramEtAl2016PPP">{{cite journal |last1=Jerram |first1=Dougal A. |last2=Widdowson |first2=Mike |last3=Wignall |first3=Paul B. |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=11 January 2023}}</ref><ref>{{cite journal |last1=Retallack |first1=Gregory J. |last2=Jahren |first2=A. Hope |date=1 October 2007 |title=Methane Release from Igneous Intrusion of Coal during Late Permian Extinction Events |url=https://www.journals.uchicago.edu/doi/epdf/10.1086/524120 |journal=[[The Journal of Geology]] |volume=116 |issue=1 |pages=1–20 |doi=10.1086/524120 |s2cid=46914712 |access-date=11 January 2023|url-access=subscription }}</ref><ref>{{cite journal |last1=Sheldon |first1=Nathan D. |last2=Chakrabarti |first2=Ramananda |last3=Retallack |first3=Gregory J. |last4=Smith |first4=Roger M. H. |date=20 February 2014 |title=Contrasting geochemical signatures on land from the Middle and Late Permian extinction events |url=https://onlinelibrary.wiley.com/doi/10.1111/sed.12117 |journal=Sedimentology |volume=61 |issue=6 |pages=1812–1829 |doi=10.1111/sed.12117 |bibcode=2014Sedim..61.1812S |hdl=2027.42/108696 |s2cid=129862176 |access-date=11 January 2023|hdl-access=free }}</ref> the [[Permian–Triassic extinction event|End-Permian Extinction Event]],<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=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=11 January 2023 |language=en |issn=1752-0908|hdl=11573/1707839 |hdl-access=free }}</ref><ref>{{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> the [[Smithian-Spathian extinction|Smithian-Spathian Extinction]],<ref>{{cite journal |last1=Paton |first1=M. T. |last2=Ivanov |first2=A. V. |last3=Fiorentini |first3=M. L. |last4=McNaughton |first4=M. J. |last5=Mudrovska |first5=I. |last6=Reznitskii |first6=L. Z. |last7=Demonterova |first7=E. 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event|Cretaceous-Palaeogene Extinction Event]],<ref name="Petersen, Sierra V. 2016">{{cite journal | last1 = Petersen|first1= Sierra V.|last2= Dutton|first2= Andrea|last3=Lohmann |first3=Kyger C. | year = 2016 | title = End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change | journal = Nature Communications | volume = 7 | page = 12079 | doi = 10.1038/ncomms12079 | pmid = 27377632 | pmc = 4935969 | bibcode = 2016NatCo...712079P}}</ref><ref>{{cite journal |author1=Keller, G. |author2=Adatte, T. |author3=Gardin, S. |author4=Bartolini, A. |author5=Bajpai, S. |title=Main Deccan volcanism phase ends near the K–T boundary: Evidence from the Krishna-Godavari Basin, SE India |year=2008 |doi=10.1016/j.epsl.2008.01.015 |journal=Earth and Planetary Science Letters |volume=268 |pages=293–311 |bibcode=2008E&PSL.268..293K |issue=3–4}}</ref><ref>{{cite web |title=Causes of the Cretaceous Extinction |website=park.org/Canada |url=http://park.org/Canada/Museum/extinction/cretcause.html}}</ref> and the [[Palaeocene-Eocene Thermal Maximum]].<ref name=Gutjahr2017>{{cite journal |last1=Gutjahr |first1=Marcus |last2=Ridgwell |first2=Andy |last3=Sexton |first3=Philip F. |last4=Anagnostou |first4=Eleni |last5=Pearson |first5=Paul N. |last6=Pälike |first6=Heiko |last7=Norris |first7=Richard D. |last8=Thomas |first8=Ellen |author8-link=Ellen Thomas (scientist) |last9=Foster |first9=Gavin L. |title=Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum |journal=Nature |date=August 2017 |volume=548 |issue=7669 |pages=573–577 |doi=10.1038/nature23646 |pmid=28858305 |pmc=5582631 |language=en |issn=1476-4687|bibcode=2017Natur.548..573G }}</ref><ref name="Kender2021">{{cite journal |last1=Kender |first1=Sev |last2=Bogus |first2=Kara |last3=Pedersen |first3=Gunver K. |last4=Dybkjær |first4=Karen |last5=Mather |first5=Tamsin A. |last6=Mariani |first6=Erica |last7=Ridgwell |first7=Andy |last8=Riding |first8=James B. |last9=Wagner |first9=Thomas |last10=Hesselbo |first10=Stephen P. |last11=Leng |first11=Melanie J. |title=Paleocene/Eocene carbon feedbacks triggered by volcanic activity |journal=Nature Communications |date=31 August 2021 |volume=12 |issue=1 |pages=5186 |doi=10.1038/s41467-021-25536-0 |pmid=34465785 |pmc=8408262 |bibcode=2021NatCo..12.5186K |language=en |issn=2041-1723|hdl=10871/126942 |hdl-access=free }}</ref><ref>{{cite journal |last1=Jones |first1=Sarah M. |last2=Hoggett |first2=Murray |last3=Greene |first3=Sarah E. |last4=Jones |first4=Tom Dunkley |date=5 December 2019 |title=Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change |journal=[[Nature Communications]] |volume=10 |issue=1 |page=5547 |doi=10.1038/s41467-019-12957-1 |pmid=31804460 |pmc=6895149 |bibcode=2019NatCo..10.5547J }}</ref> The correlation between gigantic volcanic events expressed in the large igneous provinces and mass extinctions was shown for the last 260 million years.<ref>{{cite journal | vauthors = Courtillot V | year = 1994 | title = Mass extinctions in the last 300&nbsp;million years: one impact and seven flood basalts? | journal = Israel Journal of Earth Sciences | volume = 43 | pages = 255–266 }}</ref><ref>{{cite journal | vauthors = Courtillot VE, Renne PR |title=On the ages of flood basalt events |journal=Comptes Rendus Geoscience |date=January 2003 |volume=335 |issue=1 |pages=113–140 |doi=10.1016/S1631-0713(03)00006-3 |bibcode=2003CRGeo.335..113C }}</ref> Recently such possible correlation was extended across the whole [[Phanerozoic Eon]].<ref>{{cite journal | vauthors = Kravchinsky VA |year = 2012 |title = Paleozoic large igneous provinces of Northern Eurasia: Correlation with mass extinction events |journal = Global and Planetary Change |volume = 86 |pages = 31–36 |bibcode = 2012GPC....86...31K |doi=10.1016/j.gloplacha.2012.01.007 |url=https://www.ualberta.ca/~vadim/Publications-Kravchinsky_files/2012-Kravchinsky%20-%20Paleozoic%20large%20igneous%20provinces%20of%20Northern%20Eurasia-%20Correlation%20with%20mass%20extinction%20events.pdf}}</ref>

====Sea-level fall====
These are often clearly marked by worldwide sequences of contemporaneous sediments that show all or part of a transition from sea-bed to tidal zone to beach to dry land – and where there is no evidence that the rocks in the relevant areas were raised by geological processes such as [[orogeny]]. Sea-level falls could reduce the continental shelf area (the most productive part of the oceans) sufficiently to cause a marine mass extinction, and could disrupt weather patterns enough to cause extinctions on land. But sea-level falls are very probably the result of other events, such as sustained [[global cooling]] or the sinking of the [[plate tectonics|mid-ocean ridges]].

Sea-level falls are associated with most of the mass extinctions, including all of the "Big Five"—[[Ordovician–Silurian extinction events|End-Ordovician]], [[Late Devonian extinction|Late Devonian]], [[Permian–Triassic extinction event|End-Permian]], [[Triassic–Jurassic extinction event|End-Triassic]], and [[Cretaceous–Paleogene extinction event|End-Cretaceous]], along with the more recently recognised Capitanian mass extinction of comparable severity to the Big Five.<ref name="Weidlich2002">{{cite journal| author=Weidlich, O.| year=2002| title=Permian reefs re-examined: extrinsic control mechanisms of gradual and abrupt changes during 40 my of reef evolution| url=https://www.sciencedirect.com/science/article/abs/pii/S0016699502000669| journal=[[Geobios]]| volume=35| issue=1| pages=287–294| doi=10.1016/S0016-6995(02)00066-9| bibcode=2002Geobi..35..287W| access-date=8 November 2022| url-access=subscription}}</ref><ref name="CapitanianCoralFaunas">{{cite journal |author1=Wang, X.-D. |author2=Sugiyama, T. |name-list-style=amp |title=Diversity and extinction patterns of Permian coral faunas of China |url=https://onlinelibrary.wiley.com/doi/abs/10.1080/002411600750053853 |journal=[[Lethaia]] |volume=33 |issue=4 |pages=285–294 |date=December 2000 |doi=10.1080/002411600750053853 |bibcode=2000Letha..33..285W |access-date=8 November 2022|url-access=subscription }}</ref>

A 2008 study, published in the journal ''Nature'', established a relationship between the speed of mass extinction events and changes in sea level and sediment.<ref name=Peters2008>{{cite journal | vauthors = Peters SE | title = Environmental determinants of extinction selectivity in the fossil record | journal = Nature | volume = 454 | issue = 7204 | pages = 626–629 | date = July 2008 | pmid = 18552839 | doi = 10.1038/nature07032 | s2cid = 205213600 | bibcode = 2008Natur.454..626P | url = http://doc.rero.ch/record/15860/files/PAL_E2269.pdf }}
</ref> The study suggests changes in ocean environments related to sea level exert a driving influence on rates of extinction, and generally determine the composition of life in the oceans.<ref>{{cite news |url=http://newswise.com/articles/view/541743/ |website=Newswise |title=Ebb and flow of the sea drives world's big extinction events |date=13 June 2008 |publisher=[[University of Wisconsin]] |place=Madison, WI |access-date=June 15, 2008}}</ref>

====Extraterrestrial threats====

===== Impact events =====
[[File:Impact event.jpg|thumb|alt=Meteoroid entering the atmosphere with fireball.|An artist's rendering of an [[asteroid]] a few kilometers across colliding with the Earth. Such an impact can release the equivalent energy of several million nuclear weapons detonating simultaneously.]]
The impact of a sufficiently large asteroid or comet could have caused [[food chain]]s to collapse both on land and at sea by producing dust and [[Atmospheric particulate matter|particulate]] aerosols and thus inhibiting photosynthesis.<ref>{{cite journal | vauthors = Alvarez W, Kauffman EG, Surlyk F, Alvarez LW, Asaro F, Michel HV | title = Impact theory of mass extinctions and the invertebrate fossil record | journal = Science | volume = 223 | issue = 4641 | pages = 1135–1141 | date = March 1984 | pmid = 17742919 | doi = 10.1126/science.223.4641.1135 | s2cid = 24568931 | bibcode = 1984Sci...223.1135A | jstor = 1692570 }}</ref> Impacts on [[sulfur]]-rich rocks could have emitted sulfur oxides precipitating as poisonous [[acid rain]], contributing further to the collapse of food chains. Such impacts could also have caused [[megatsunami]]s and/or global [[forest fire]]s.

Most paleontologists now agree that an asteroid did hit the Earth about 66&nbsp;Ma, but there is lingering dispute whether the impact was the sole cause of the [[Cretaceous–Paleogene extinction event]].<ref name="Keller_2009">{{cite journal |vauthors=Keller G, Abramovich S, Berner Z, Adatte T |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=271 |issue=1–2 |date=1 January 2009 |pages=52–68 |title=Biotic effects of the Chicxulub impact, K–T catastrophe and sea level change in Texas |doi=10.1016/j.palaeo.2008.09.007 |bibcode=2009PPP...271...52K}}</ref><ref name="Morgan">{{cite journal |title=Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub |vauthors=Morgan J, Lana C, Kersley A, Coles B, Belcher C, Montanari S, Diaz-Martinez E, Barbosa A, Neumann V |journal=Earth and Planetary Science Letters |volume=251 |issue=3–4 |year=2006 |pages=264–279 |doi=10.1016/j.epsl.2006.09.009 |bibcode=2006E&PSL.251..264M|url=http://spiral.imperial.ac.uk/bitstream/10044/1/1208/1/EPSL-D-05-00905%5b1%5d.pdf |hdl=10044/1/1208 }}</ref> Nonetheless, in October 2019, researchers reported that the [[Chicxulub impactor|Cretaceous Chicxulub asteroid impact]] that resulted in the [[Cretaceous–Paleogene extinction event|extinction]] of non-avian [[dinosaurs]] 66&nbsp;Ma, also rapidly [[Ocean acidification|acidified the oceans]], producing [[ecological collapse]] and long-lasting effects on the climate, and was a key reason for end-Cretaceous mass extinction.<ref name="NYT-20191021">{{cite news | vauthors = Joel L |date=21 October 2019 |title=The dinosaur-killing asteroid acidified the ocean in a flash: The Chicxulub event was as damaging to life in the oceans as it was to creatures on land, a study shows |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2019/10/21/science/chicxulub-asteroid-ocean-acid.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2019/10/21/science/chicxulub-asteroid-ocean-acid.html |archive-date=2022-01-01 |url-access=limited |access-date=22 October 2019 }}{{cbignore}}</ref><ref name="PNAS-20191021">{{cite journal | vauthors = Henehan MJ, Ridgwell A, Thomas E, Zhang S, Alegret L, Schmidt DN, Rae JW, Witts JD, Landman NH, Greene SE, Huber BT, Super JR, Planavsky NJ, Hull PM | display-authors = 6 | title = Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact | journal =  Proceedings of the National Academy of Sciences| volume = 116 | issue = 45 | pages = 22500–22504 | date = November 2019 | pmid = 31636204 | pmc = 6842625 | doi = 10.1073/pnas.1905989116 | doi-access = free | bibcode = 2019PNAS..11622500H }}</ref>

The [[Permian-Triassic extinction event]] has also been hypothesised to have been caused by an asteroid impact that formed the [[Araguainha crater]] due to the estimated date of the crater's formation overlapping with the end-Permian extinction event.<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=12 January 2023}}</ref><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=GSA Bulletin |volume=130 |issue=7–8 |pages=1099–1120 |doi=10.1130/B31626.1 |bibcode=2018GSAB..130.1099T |access-date=12 January 2023|url-access=subscription }}</ref><ref name=Tohver_2012>{{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> However, this hypothesis has been widely challenged, with the impact hypothesis being rejected by most researchers.<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 | volume=293 | issue=5539 | year=2001 | pages=2343a–2343 | doi=10.1126/science.293.5539.2343a | pmid=11577203
|doi-access=free }}</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 | volume=32 | issue=12 | year=2004 | pages=1053–1056 |doi=10.1130/G20907.1
|bibcode = 2004Geo....32.1053K }}</ref><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=12 January 2023|url-access=subscription }}</ref>

According to the [[Shiva hypothesis]], the Earth is subject to increased asteroid impacts about once every 27&nbsp;million years because of the Sun's passage through the plane of the [[Milky Way]] galaxy, thus causing extinction events at 27&nbsp;million year intervals. Some evidence for this hypothesis has emerged in both marine and non-marine contexts.<ref>{{cite journal | vauthors = Rampino M, Caldeira K, Zhu Y |doi= 10.1080/08912963.2020.1849178 |title=A 27.5&nbsp;My underlying periodicity detected in extinction episodes of non-marine tetrapods |journal=[[Historical Biology]] |date=December 2020 |volume=33 |issue=11 |pages=3084–3090 |s2cid=230580480}}</ref> Alternatively, the Sun's passage through the higher density spiral arms of the galaxy could coincide with mass extinction on Earth, perhaps due to increased [[impact events]].<ref name="extinction">{{Cite journal | vauthors = Gillman M, Erenler H |title=The galactic cycle of extinction |journal=[[International Journal of Astrobiology]] |volume=7 |issue=1 |pages=17–26 |date=2008 |doi=10.1017/S1473550408004047|bibcode=2008IJAsB...7...17G |url=http://oro.open.ac.uk/11603/1/S1473550408004047a.pdf |citeseerx=10.1.1.384.9224|s2cid=31391193 }}</ref> However, a reanalysis of the effects of the Sun's transit through the spiral structure based on maps of the spiral structure of the Milky Way in CO molecular line emission has failed to find a correlation.<ref>{{cite journal | vauthors = Overholt AC, Melott AL, Pohl M |title=Testing the Link Between Terrestrial Climate Change and Galactic Spiral Arm Transit |journal=The Astrophysical Journal |date=10 November 2009 |volume=705 |issue=2 |pages=L101–L103|arxiv=0906.2777|s2cid=734824 |doi=10.1088/0004-637X/705/2/L101|bibcode=2009ApJ...705L.101O }}</ref>

==== A nearby nova, supernova or gamma ray burst ====
A nearby [[gamma-ray burst]] (less than 6000 [[light-year]]s away) would be powerful enough to destroy the Earth's [[ozone layer]], leaving organisms vulnerable to [[Ultraviolet|ultraviolet radiation]] from the Sun.<ref name="20 ways">{{cite web | vauthors = Powell CS |author-link=Corey S. Powell |date=2001-10-01 |title=20 Ways the World Could End |url=http://discovermagazine.com/2000/oct/featworld/article_view?b_start:int=0&-C= |access-date=2011-03-29 |publisher=Discover Magazine}}</ref> Gamma ray bursts are fairly rare, occurring only a few times in a given galaxy per million years.<ref>{{cite journal | vauthors = Podsiadlowski P, Mazzali PA, Nomoto K, Lazzati D, Cappellaro E |year=2004 |title=The Rates of Hypernovae and Gamma-Ray Bursts: Implications for Their Progenitors |journal=[[Astrophysical Journal Letters]] |volume=607 |issue=1 |page=L17 |arxiv=astro-ph/0403399 |bibcode=2004ApJ...607L..17P |doi=10.1086/421347 |s2cid=119407415}}</ref>
It has been suggested that a gamma ray burst caused the [[Ordovician–Silurian extinction events|End-Ordovician]] extinction,<ref>{{cite journal |last1=Melott |first1=Adrian L. |last2=Lieberman |first2=B. S. |last3=Laird |first3=Claude M. |last4= Martin |first4=L. D. |last5=Medvedev |first5=M. V. |last6=Thomas |first6=Brian C. |last7=Cannizzo |first7=John K. |last8=Gehrels |first8=Neil |last9=Jackman |first9=Charles H. |url=https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/abs/did-a-gammaray-burst-initiate-the-late-ordovician-mass-extinction/F37A58C811EB82496CEF6CF989159807 |title=Did a gamma-ray burst initiate the late Ordovician mass extinction? |journal=International Journal of Astrobiology |date=5 August 2004 |volume=3 | issue=2 | pages=55–61 |arxiv=astro-ph/0309415 |doi=10.1017/S1473550404001910 |bibcode=2004IJAsB...3...55M |hdl=1808/9204 |s2cid=13124815 |access-date=27 December 2022}}</ref><ref name="Melott & Thomas 2009">{{cite journal | vauthors = Melott AL, Thomas BC |year=2009 |title=Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionizing radiation damage |journal=Paleobiology |volume=35 |issue=3 |pages=311–20 |arxiv=0809.0899 |doi=10.1666/0094-8373-35.3.311 |bibcode=2009Pbio...35..311M |s2cid=11942132}}</ref> while a supernova has been proposed as the cause of the [[Hangenberg event]].<ref>{{Cite journal|last1=Fields|first1=Brian D.|last2=Melott|first2=Adrian L.|last3=Ellis|first3=John|last4=Ertel|first4=Adrienne F.|last5=Fry|first5=Brian J.|last6=Lieberman|first6=Bruce S.|last7=Liu|first7=Zhenghai|last8=Miller|first8=Jesse A.|last9=Thomas|first9=Brian C.|date=2020-09-01|title=Supernova triggers for end-Devonian extinctions|journal= Proceedings of the National Academy of Sciences|language=en|volume=117|issue=35|pages=21008–21010|doi=10.1073/pnas.2013774117| arxiv=2007.01887|issn=0027-8424|pmid=32817482|pmc=7474607|bibcode=2020PNAS..11721008F |doi-access=free }}</ref> A supernova within 25 light-years would strip Earth of its atmosphere. Today there is in the Solar System's neighbourhood no critical star capable to produce a supernova dangerous to life on Earth.<ref name="ESO Supernova Exhibition f453">{{cite web | title=ESO Supernova | website=ESO Supernova Exhibition | url=https://supernova.eso.org/exhibition/1218/#:~:text=If%20a%20supernova%20explosion%20were,there's%20no%20reason%20to%20worry. | access-date=2024-04-08}}</ref>

====Global cooling====
Sustained and significant global cooling could kill many [[Polar circle|polar]] and [[temperate]] species and force others to migrate towards the [[equator]]; reduce the area available for [[Tropics|tropical]] species; often make the Earth's climate more arid on average, mainly by locking up more of the planet's water in ice and snow. The [[glaciation]] cycles of the [[current ice age]] are believed to have had only a very mild impact on biodiversity, so the mere existence of a significant cooling is not sufficient on its own to explain a mass extinction.

It has been suggested that global cooling caused or contributed to the [[Ordovician–Silurian extinction events|End-Ordovician]], [[Permian–Triassic extinction event|Permian–Triassic]], [[Late Devonian extinction|Late Devonian]] extinctions, and possibly others. Sustained global cooling is distinguished from the temporary climatic effects of flood basalt events or impacts.

====Global warming====
{{Main|Extinction risk from global warming}}
This would have the opposite effects: expand the area available for [[Tropics|tropical]] species; kill [[temperate]] species or force them to migrate towards the [[Polar circle|poles]]; possibly cause severe extinctions of polar species; often make the Earth's climate wetter on average, mainly by melting ice and snow and thus increasing the volume of the [[water cycle]]. It might also cause anoxic events in the oceans (see below).

Global warming as a cause of mass extinction is supported by several recent studies.<ref>{{cite journal | vauthors = Mayhew PJ, Jenkins GB, Benton TG | title = A long-term association between global temperature and biodiversity, origination and extinction in the fossil record | journal = Proceedings. Biological Sciences | volume = 275 | issue = 1630 | pages = 47–53 | date = January 2008 | pmid = 17956842 | pmc = 2562410 | doi = 10.1098/rspb.2007.1302 }}</ref>

The most dramatic example of sustained warming is the [[Paleocene–Eocene Thermal Maximum]], which was associated with one of the smaller mass extinctions. It has also been suggested to have caused the [[Triassic–Jurassic extinction event]], during which 20% of all marine families became extinct. Furthermore, the [[Permian–Triassic extinction event]] has been suggested to have been caused by warming.<ref>{{cite journal | vauthors = Knoll AH, Bambach RK, Canfield DE, Grotzinger JP | title = Comparative Earth History and Late Permian Mass Extinction | journal = Science | volume = 273 | issue = 5274 | pages = 452–457 | date = July 1996 | pmid = 8662528 | doi = 10.1126/science.273.5274.452 | s2cid = 35958753 | bibcode = 1996Sci...273..452K }}</ref><ref>{{cite journal | vauthors = Ward PD, Botha J, Buick R, De Kock MO, Erwin DH, Garrison GH, Kirschvink JL, Smith R | display-authors = 6 | title = Abrupt and gradual extinction among Late Permian land vertebrates in the Karoo basin, South Africa | journal = Science | volume = 307 | issue = 5710 | pages = 709–714 | date = February 2005 | pmid = 15661973 | doi = 10.1126/science.1107068 | s2cid = 46198018 | citeseerx = 10.1.1.503.2065 | bibcode = 2005Sci...307..709W }}</ref><ref>{{cite journal | vauthors = Kiehl JT, Shields CA |date=September 2005 |title=Climate simulation of the latest Permian: Implications for mass extinction |journal=Geology |volume=33 |issue=9 |pages=757–760|doi=10.1130/G21654.1 |bibcode = 2005Geo....33..757K }}</ref>

===== Clathrate gun hypothesis =====
{{Main|Clathrate gun hypothesis}}
[[Clathrates]] are composites in which a lattice of one substance forms a cage around another. [[Methane clathrate]]s (in which water molecules are the cage) form on [[continental shelf|continental shelves]]. These clathrates are likely to break up rapidly and release the methane if the temperature rises quickly or the pressure on them drops quickly – for example in response to sudden [[global warming]] or a sudden drop in sea level or even [[earthquake]]s. Methane is a much more powerful [[greenhouse effect|greenhouse]] gas than carbon dioxide, so a methane eruption ("clathrate gun") could cause rapid global warming or make it much more severe if the eruption was itself caused by global warming.

The most likely signature of such a methane eruption would be a sudden decrease in the [[Isotope analysis|ratio of carbon-13 to carbon-12]] in sediments, since methane clathrates are low in carbon-13; but the change would have to be very large, as other events can also reduce the percentage of carbon-13.<ref>{{cite magazine | vauthors = Hecht J | title=Methane prime suspect for greatest mass extinction | magazine=[[New Scientist]] | date=2002-03-26 | url=https://www.newscientist.com/article/dn2088-methane-prime-suspect-for-greatest-mass-extinction/}}</ref>

It has been suggested that "clathrate gun" methane eruptions were involved in the [[Permian–Triassic extinction event|end-Permian extinction]] ("the Great Dying") and in the [[Paleocene–Eocene Thermal Maximum]], which was associated with one of the smaller mass extinctions.

====Anoxic events====
[[Anoxic event]]s are situations in which the middle and even the upper layers of the ocean become deficient or totally lacking in oxygen. Their causes are complex and controversial, but all known instances are associated with severe and sustained global warming, mostly caused by sustained massive volcanism.<ref>{{cite journal |title = Geochemistry of oceanic anoxic events |journal = Geochemistry, Geophysics, Geosystems |date = 2010-03-01 |issn = 1525-2027 |pages = Q03004 |volume = 11|issue = 3|doi = 10.1029/2009GC002788 | vauthors = Jenkyns HC |bibcode=2010GGG....11.3004J|s2cid = 128598428 }}</ref>

It has been suggested that anoxic events caused or contributed to the [[Ordovician–Silurian extinction events|Ordovician–Silurian]],<ref name="QiuEtAl2022CommsEarthEnvironment">{{cite journal |last1=Qiu |first1=Zhen |last2=Zou |first2=Caineng |last3=Mills |first3=Benjamin J. W. |last4=Xiong |first4=Yijun |last5=Tao |first5=Huifei |last6=Lu |first6=Bin |last7=Liu |first7=Hanlin |last8=Xiao |first8=Wenjiao |last9=Poulton |first9=Simon W. |date=5 April 2022 |title=A nutrient control on expanded anoxia and global cooling during the Late Ordovician mass extinction |journal=[[Communications Earth & Environment]] |volume=3 |issue=1 |page=82 |doi=10.1038/s43247-022-00412-x |bibcode=2022ComEE...3...82Q |s2cid=247943064 |doi-access=free }}</ref><ref name=":12">{{Cite journal|last1=Zou|first1=Caineng|last2=Qiu|first2=Zhen|last3=Poulton|first3=Simon W.|last4=Dong|first4=Dazhong|last5=Wang|first5=Hongyan|last6=Chen|first6=Daizhou|last7=Lu|first7=Bin|last8=Shi|first8=Zhensheng|last9=Tao|first9=Huifei|date=2018|title=Ocean euxinia and climate change "double whammy" drove the Late Ordovician mass extinction|url=http://eprints.whiterose.ac.uk/129520/2/Revised%20Manuscript%20G40121.pdf|journal=[[Geology (journal)|Geology]]|volume=46|issue=6|pages=535–538|doi=10.1130/G40121.1|bibcode=2018Geo....46..535Z|s2cid=135039656 }}</ref><ref>{{cite journal |last1=Men |first1=Xin |last2=Mou |first2=Chuanlong |last3=Ge |first3=Xiangying |date=1 August 2022 |title=Changes in palaeoclimate and palaeoenvironment in the Upper Yangtze area (South China) during the Ordovician–Silurian transition |journal=[[Scientific Reports]] |volume=12 |issue=1 |page=13186 |doi=10.1038/s41598-022-17105-2 |pmid=35915216 |pmc=9343391 |bibcode=2022NatSR..1213186M }}</ref> [[Late Devonian extinction|late Devonian]],<ref>{{cite journal |last1=Bond |first1=David P. G. |last2=Zatoń |first2=Michał |last3=Wignall |first3=Paul B. |last4=Marynowski |first4=Leszek |date=11 March 2013 |title=Evidence for shallow-water 'Upper Kellwasser' anoxia in the Frasnian–Famennian reefs of Alberta, Canada |url=https://onlinelibrary.wiley.com/doi/full/10.1111/let.12014 |journal=[[Lethaia]] |volume=46 |issue=3 |pages=355–368 |doi=10.1111/let.12014 |bibcode=2013Letha..46..355B |access-date=12 January 2023|url-access=subscription }}</ref><ref name=Algeo1998>{{cite journal|author=Algeo, T.J.|year=1998|title=Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=353|issue=1365|pages=113–130|doi=10.1098/rstb.1998.0195|last2=Scheckler|first2=S. E.|pmc=1692181}}</ref><ref name=Bond2008>{{cite journal|doi=10.1016/j.palaeo.2008.02.015|title=The role of sea-level change and marine anoxia in the Frasnian-Famennian (Late Devonian) mass extinction|year=2008|author1=David P. G. Bond |author2=Paul B. Wignalla |volume=263|journal=  Palaeogeography, Palaeoclimatology, Palaeoecology|pages=107–118|issue=3–4|bibcode=2008PPP...263..107B|url=http://eprints.whiterose.ac.uk/3460/1/bondb2.pdf}}</ref> [[Capitanian mass extinction event|Capitanian]],<ref>{{cite journal |last1=Zhang |first1=Bolin |last2=Wignall |first2=Paul B. |last3=Yao |first3=Suping |last4=Hu |first4=Wenxuan |last5=Liu |first5=Biao |date=January 2021 |title=Collapsed upwelling and intensified euxinia in response to climate warming during the Capitanian (Middle Permian) mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S1342937X20302446 |journal=[[Gondwana Research]] |volume=89 |pages=31–46 |doi=10.1016/j.gr.2020.09.003 |bibcode=2021GondR..89...31Z |s2cid=224981591 |access-date=30 September 2022|url-access=subscription }}</ref><ref>{{cite journal |last1=Zhang |first1=Bolin |last2=Yao |first2=Suping |last3=Hu |first3=Wenxuan |last4=Ding |first4=Hai |last5=Liu |first5=Bao |last6=Ren |first6=Yongle |date=1 October 2019 |title=Development of a high-productivity and anoxic-euxinic condition during the late Guadalupian in the Lower Yangtze region: Implications for the mid-Capitanian extinction event |url=https://www.sciencedirect.com/science/article/abs/pii/S003101821730977X |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=531 |page=108630 |doi=10.1016/j.palaeo.2018.01.021 |bibcode=2019PPP...53108630Z |s2cid=133916878 |access-date=17 November 2022|url-access=subscription }}</ref><ref name="BondWignallGrasby2019">{{cite journal |last1=Bond |first1=David P. G. |last2=Wignall |first2=Paul B. |last3=Grasby |first3=Stephen E. |date=30 August 2019 |title=The Capitanian (Guadalupian, Middle Permian) mass extinction in NW Pangea (Borup Fiord, Arctic Canada): A global crisis driven by volcanism and anoxia |journal=[[Geological Society of America Bulletin]] |volume=132 |issue=5–6 |pages=931–942 |doi=10.1130/B35281.1 |s2cid=199104686 |doi-access=free }}</ref> [[Permian–Triassic extinction event|Permian–Triassic]],<ref name=Kump2005>{{cite journal|last=Kump|first=Lee |author2=Alexander Pavlov |author3=Michael A. Arthur|title=Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia|journal=Geology|year=2005|volume=33|issue=5 |pages=397–400|doi=10.1130/G21295.1|bibcode=2005Geo....33..397K}}</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=12 January 2023}}</ref><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 B. |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=12 January 2023|hdl-access=free }}</ref> and [[Triassic–Jurassic extinction event|Triassic–Jurassic]] extinctions,<ref>{{cite journal |last1=Atkinson |first1=J. W. |last2=Wignall |first2=Paul B. |date=15 August 2019 |title=How quick was marine recovery after the end-Triassic mass extinction and what role did anoxia play? |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018219302330 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=528 |pages=99–119 |doi=10.1016/j.palaeo.2019.05.011 |bibcode=2019PPP...528...99A |s2cid=164911938 |access-date=20 December 2022}}</ref> as well as a number of lesser extinctions (such as the [[Ireviken event|Ireviken]], [[Lundgreni Event|Lundgreni]], [[Mulde event|Mulde]], [[Lau event|Lau]], [[Smithian-Spathian boundary extinction|Smithian-Spathian]], [[Toarcian turnover|Toarcian]], and [[Cenomanian-Turonian boundary event|Cenomanian–Turonian]] events). On the other hand, there are widespread black shale beds from the mid-Cretaceous that indicate anoxic events but are not associated with mass extinctions.

The [[bio-availability]] of [[Essential trace element|essential]] [[trace element]]s (in particular [[selenium]]) to potentially lethal lows has been shown to coincide with, and likely have contributed to, at least three mass extinction events in the oceans, that is, at the end of the Ordovician, during the Middle and Late Devonian, and at the end of the Triassic. During periods of low oxygen concentrations very soluble [[selenate]] (Se<sup>6+</sup>) is converted into much less soluble [[selenide]] (Se<sup>2-</sup>), elemental Se and organo-selenium complexes. Bio-availability of selenium during these extinction events dropped to about 1% of the current oceanic concentration, a level that has been proven lethal to many [[Extant taxon|extant]] organisms.<ref>{{cite journal | vauthors = Long JA, Large RR, Lee MS, Benton MJ, Danyushevsky LV, Chiappe LM, Halpin JA, Cantrill D, Lottermoser B |display-authors=6 |year=2015 |title=Severe selenium depletion in the Phanerozoic oceans as a factor in three global mass extinction events |journal= Gondwana Research |volume=36 |pages= 209–218 |doi=10.1016/j.gr.2015.10.001 |bibcode=2016GondR..36..209L |url=https://research-information.bristol.ac.uk/en/publications/severe-selenium-depletion-in-the-phanerozoic-oceans-as-a-factor-in-three-global-mass-extinction-events(68e97709-15fb-496b-b28d-f8ea9ea9b4fc).html |hdl=1983/68e97709-15fb-496b-b28d-f8ea9ea9b4fc|s2cid=129753283 |hdl-access=free }}</ref>

British [[oceanologist]] and [[atmospheric scientist]], [[Andrew Watson (scientist)|Andrew Watson]], explained that, while the [[Holocene|Holocene epoch]] exhibits many processes reminiscent of those that have contributed to past anoxic events, full-scale ocean anoxia would take "thousands of years to develop".<ref>{{cite journal | vauthors = Watson AJ | title = Oceans on the edge of anoxia | journal = Science | volume = 354 | issue = 6319 | pages = 1529–1530 | date = December 2016 | pmid = 28008026 | doi = 10.1126/science.aaj2321 | language = en | s2cid = 206653923 | bibcode = 2016Sci...354.1529W | hdl = 10871/25100 | hdl-access = free }}</ref>

====Hydrogen sulfide emissions from the seas====
Kump, Pavlov and Arthur (2005) have proposed that during the [[Permian–Triassic extinction event]] the warming also upset the oceanic balance between [[photosynthesis]]ing plankton and deep-water [[sulfate-reducing bacteria]], causing massive emissions of [[hydrogen sulfide]], which poisoned life on both land and sea and severely weakened the [[ozone layer]], exposing much of the life that still remained to fatal levels of [[UV radiation]].<ref>{{cite journal | vauthors = Berner RA, Ward PD |title=Positive Reinforcement, H2S, and the Permo-Triassic Extinction: Comment and Reply: COMMENT |journal=Geology |date=1 January 2006 |volume=34 |issue=1 |pages=e100 |doi=10.1130/G22641.1 |bibcode=2006Geo....34E.100B |doi-access=free }}</ref><ref>{{cite journal | vauthors = Kump LR, Pavlov A, Arthur MA | year = 2005 | title = Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia | journal = Geology | volume = 33 | issue = 5| pages = 397–400 | doi=10.1130/g21295.1 |bibcode = 2005Geo....33..397K }} Summarised by Ward (2006).</ref><ref name="Ward 2006"/>

====Oceanic overturn====
Oceanic overturn is a disruption of [[thermo-haline circulation]] that lets surface water (which is more saline than deep water because of evaporation) sink straight down, bringing anoxic deep water to the surface and therefore killing most of the oxygen-breathing organisms that inhabit the surface and middle depths. It may occur either at the beginning or the end of a [[glaciation]], although an overturn at the start of a glaciation is more dangerous because the preceding warm period will have created a larger volume of anoxic water.<ref>{{cite journal | vauthors = Wilde P, Berry WB | title=Destabilization of the oceanic density structure and its significance to marine "extinction" events | journal=Palaeogeography, Palaeoclimatology, Palaeoecology | volume=48 | issue=2–4 | pages=143–62 | year=1984 | url=http://www.marscigrp.org/ppp84.html | doi=10.1016/0031-0182(84)90041-5 | bibcode=1984PPP....48..143W | url-access=subscription }}</ref>

Unlike other oceanic catastrophes such as regressions (sea-level falls) and anoxic events, overturns do not leave easily identified "signatures" in rocks and are theoretical consequences of researchers' conclusions about other climatic and marine events.

It has been suggested that oceanic overturn caused or contributed to the [[Late Devonian extinction|late Devonian]] and [[Permian–Triassic extinction event|Permian–Triassic]] extinctions.

====Geomagnetic reversal====
One theory is that periods of increased [[geomagnetic reversal]]s will weaken [[Earth's magnetic field]] long enough to expose the atmosphere to the [[solar wind]]s, causing oxygen ions to escape the atmosphere in a rate increased by 3–4 orders, resulting in a disastrous decrease in oxygen.<ref>{{cite journal|title=Oxygen escape from the Earth during geomagnetic reversals: Implications to mass extinction | vauthors = Wei Y, Pu Z, Zong Q, Wan W, Ren Z, Fraenz M, Dubinin E, Tian F, Shi Q, Fu S, Hong M | display-authors = 6 |date=1 May 2014|journal=Earth and Planetary Science Letters|volume=394|pages=94–98|via=NASA ADS |doi=10.1016/j.epsl.2014.03.018 |bibcode=2014E&PSL.394...94W|doi-access=free}}</ref>

====Plate tectonics====
Movement of the continents into some configurations can cause or contribute to extinctions in several ways: by initiating or ending [[ice age]]s; by changing ocean and wind currents and thus altering climate; by opening seaways or land bridges that expose previously isolated species to competition for which they are poorly adapted (for example, the extinction of most of South America's [[Meridiungulata|native ungulates]] and all of its [[Sparassodonta|large metatherians]] after the [[Great American Interchange|creation of a land bridge between North and South America]]). Occasionally continental drift creates a super-continent that includes the vast majority of Earth's land area, which in addition to the effects listed above is likely to reduce the total area of [[continental shelf]] (the most species-rich part of the ocean) and produce a vast, arid continental interior that may have extreme seasonal variations.

Another theory is that the creation of the super-continent [[Pangaea]] contributed to the [[Permian-Triassic extinction event|End-Permian]] mass extinction. Pangaea was almost fully formed at the transition from mid-Permian to late-Permian, and the "Marine genus diversity" diagram at the top of this article shows a level of extinction starting at that time, which might have qualified for inclusion in the "Big Five" if it were not overshadowed by the "Great Dying" at the end of the Permian.<ref>{{cite web |title=Speculated Causes of the Permian Extinction |publisher=Hooper Virtual Paleontological Museum |url=http://park.org/Canada/Museum/extinction/permcause.html |access-date=16 July 2012}}</ref>

====Human activities====
[[File:Ice_age_fauna_of_northern_Spain_-_Mauricio_Antón.jpg|thumb|The [[Late Pleistocene]] saw [[Quaternary extinction event|extinction]]s of numerous predominantly [[megafauna]]l species, coinciding in time with the [[early human migrations]] across continents.<ref>{{cite journal |last1= Smith|first1=Felisa A.|display-authors=etal.|date=April 20, 2018 |title=Body size downgrading of mammals over the late Quaternary|journal=Science |volume=360 |issue=6386|pages=310–313|doi=10.1126/science.aao5987 |pmid=29674591|bibcode=2018Sci...360..310S |doi-access=free}}</ref>]]
Scientists have been concerned that human activities could cause more plants and animals to become extinct than any point in the past. Along with human-made changes in climate (see above), some of these extinctions could be caused by overhunting, overfishing, invasive species, or habitat loss. A study published in May 2017 in ''[[Proceedings of the National Academy of Sciences of the United States of America|Proceedings of the National Academy of Sciences]]'' argued that a "biological annihilation" akin to a [[Holocene extinction|sixth mass extinction event]] is underway as a result of anthropogenic causes, such as [[Human overpopulation|over-population]] and [[Overconsumption|over-consumption]]. The study suggested that as much as 50% of the number of animal individuals that once lived on Earth were already extinct, threatening the basis for human existence too.<ref>{{cite journal | vauthors = Ceballos G, Ehrlich PR, Dirzo R | title = Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines | journal =  Proceedings of the National Academy of Sciences| volume = 114 | issue = 30 | pages = E6089–E6096 | date = July 2017 | pmid = 28696295 | pmc = 5544311 | doi = 10.1073/pnas.1704949114 | bibcode = 2017PNAS..114E6089C | doi-access = free }}</ref><ref name="Sutter">{{cite news | vauthors = Sutter JD |date=July 11, 2017|title=Sixth mass extinction: The era of 'biological annihilation'|url=http://www.cnn.com/2017/07/11/world/sutter-mass-extinction-ceballos-study/index.html |website=[[CNN]] |access-date=July 17, 2017}}</ref>

====Other hypotheses====
[[File:Terra Indígena Porquinhos, Maranhão (25758143568).jpg|thumb|Many species of plants and animals are at high risk of extinction due to the [[Deforestation of the Amazon rainforest|destruction]] of the [[Amazon rainforest]]]]
Many other hypotheses have been proposed, such as the spread of a new disease, or simple out-competition following an especially successful biological innovation. But all have been rejected, usually for one of the following reasons: they require events or processes for which there is no evidence; they assume mechanisms that are contrary to the available evidence; they are based on other theories that have been rejected or superseded.

====Future biosphere extinction/sterilization====
{{See also|Future of Earth|Medea hypothesis}}
The eventual warming and expanding of the Sun, combined with the eventual decline of atmospheric carbon dioxide, could actually cause an even greater mass extinction, having the potential to wipe out even microbes (in other words, the Earth would be completely sterilized): rising global temperatures caused by the expanding Sun would gradually increase the rate of weathering, which would in turn remove more and more CO<sub>2</sub> from the atmosphere. When CO<sub>2</sub> levels get too low (perhaps at 50 ppm), most plant life will die out, although simpler plants like grasses and mosses can survive much longer, until {{CO2}} levels drop to 10 ppm.<ref name= Franck2005>{{cite journal | vauthors = Franck S, Bounama C, von Bloh W | year = 2006 | title = Causes and Timing of Future Biosphere Extinction | journal = Biogeosciences | volume = 3 | issue = 1 | pages = 85–92 | bibcode = 2006BGeo....3...85F | doi = 10.5194/bg-3-85-2006 | s2cid = 129600368 | url = http://hal.archives-ouvertes.fr/docs/00/29/75/42/PDF/bg-3-85-2006.pdf | doi-access = free }}</ref><ref name=Ward2003>{{cite book | vauthors = Ward P, Brownlee D | date = December 2003 | title = The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of Our World | publisher = Henry Holt and Co | isbn = 978-0-8050-7512-0 | pages = 132, 139, 141 | url = https://books.google.com/books?id=3D4vHo4nDtYC | via = Google Books }}</ref>

With all photosynthetic organisms gone, atmospheric oxygen can no longer be replenished, and it is eventually removed by chemical reactions in the atmosphere, perhaps from volcanic eruptions. Eventually the loss of oxygen will cause all remaining aerobic life to die out via asphyxiation, leaving behind only simple anaerobic [[prokaryote]]s. When the Sun becomes 10% brighter in about a billion years,<ref name= Franck2005/> Earth will suffer a moist greenhouse effect resulting in its oceans boiling away, while the Earth's liquid outer core cools due to the inner core's expansion and causes the Earth's magnetic field to shut down. In the absence of a magnetic field, charged particles from the Sun will deplete the atmosphere and further increase the Earth's temperature to an average of around 420 K (147&nbsp;°C, 296&nbsp;°F) in 2.8 billion years, causing the last remaining life on Earth to die out. This is the most extreme instance of a climate-caused extinction event. Since this will only happen late in the Sun's life, it would represent the final mass extinction in Earth's history (albeit a very long extinction event).<ref name= Franck2005/><ref name=Ward2003/>