Editing Extinction event

{{Short description|Widespread and rapid decrease in the biodiversity on Earth}}
{{About|mass extinction|other uses|Extinction Event (disambiguation)}}
{{Annotated image/Extinction |caption=The blue graph shows the apparent ''percentage'' (not the absolute number) of marine [[animal]] [[genus|genera]] becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised [[Capitanian mass extinction event]] are clickable links. The two extinction events occurring in the Cambrian (far left) are very large in percentage magnitude, but small in absolute numbers of known taxa due to the relative scarcity of fossil-producing life at that time. ''([[:Image:Extinction intensity.svg|source and image info]])''}}
{{use dmy dates|date=January 2022}}
An '''extinction event''' (also known as a '''mass extinction''' or '''biotic crisis''') is a widespread and rapid decrease in the [[biodiversity]] on [[Earth]]. Such an event is identified by a sharp fall in the diversity and abundance of [[multicellular organism]]s. It occurs when the rate of [[extinction]] increases with respect to the [[background extinction rate]]<ref name=Sudakow2022>{{cite journal |last1=Sudakow |first1=Ivan |last2=Myers |first2=Corinne |last3=Petrovskii |first3=Sergei |last4=Sumrall |first4=Colin D. |last5=Witts |first5=James |date=July 2022 |title=Knowledge gaps and missing links in understanding mass extinctions: Can mathematical modeling help? |journal=Physics of Life Reviews |volume=41 |pages=22–57 |doi=10.1016/j.plrev.2022.04.001 |pmid=35523056 |bibcode=2022PhLRv..41...22S |s2cid=248215038 |doi-access=free }}</ref> and the rate of [[speciation]]. 

Estimates of the number of major mass extinctions in the last 540&nbsp;million years range from as few as five to more than twenty. These differences stem from disagreement as to what constitutes a "major" extinction event, and the data chosen to measure past diversity.

==The "Big Five" mass extinctions==
In a landmark paper published in 1982, [[Jack Sepkoski]] and [[David M. Raup]] identified five particular geological intervals with excessive diversity loss.<ref name= Raup/> They were originally identified as outliers on a general trend of decreasing extinction rates during the [[Phanerozoic]],<ref name=Alroy_2008/> but as more stringent statistical tests have been applied to the accumulating data, it has been established that in the current, Phanerozoic Eon, multicellular animal life has experienced at least five major and many minor mass extinctions.<ref>{{cite magazine |last=Gould |first=S.J. |author-link=Stephen Jay Gould |date=October 1994 |title=The evolution of life on Earth |magazine=[[Scientific American]] |volume=271 |issue=4 |pages=84–91 |pmid=7939569 |doi=10.1038/scientificamerican1094-84 |bibcode=1994SciAm.271d..84G}}</ref> The "Big Five" cannot be so clearly defined, but rather appear to represent the largest (or some of the largest) of a relatively smooth continuum of extinction events.<ref name=Alroy_2008/> All of the five in the Phanerozoic Eon were anciently preceded by the presumed far more extensive mass extinction of microbial life during the [[Great Oxidation Event]] (a.k.a. Oxygen Catastrophe) early in the [[Proterozoic Eon]]. At the end of the [[Ediacaran]] and just before the [[Cambrian explosion]], yet another Proterozoic extinction event (of unknown magnitude) is speculated to have ushered in the Phanerozoic.<ref>{{cite journal |first1=Scott D. |last1=Evans |first2=Chenyi |last2=Tu |first3=Adriana |last3= Rizzo |first4=Mary L. |last4=Droser |date=7 November 2022 |title=Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition |journal= Proceedings of the National Academy of Sciences|volume=119 |issue=46 |page=e2207475119 |doi=10.1073/pnas.2207475119|doi-access=free |pmid=36343248 |pmc=9674242 |bibcode=2022PNAS..11907475E }}</ref>

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{|
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|style="vertical-align:top;text-align:center;width:2%;" rowspan="2"| {{big|'''{{math|1}}'''}} 
|style="vertical-align:top;text-align:left;width:40%;"| '''[[Late Ordovician mass extinction]]'''
|style="vertical-align:top;text-align:left;"| 445–444&nbsp;[[Megaannum|Ma]]
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|style="vertical-align:top;text-align:left;" colspan="3"| End Ordovician or O–S, just prior to and at the [[Ordovician]]–[[Silurian]] transition. Two events occurred that killed off 27% of all [[family (biology)|families]], 57% of all genera and 85% of all [[species]].<ref name="ucr">{{cite web|url=http://math.ucr.edu/home/baez/extinction |title=extinction |publisher= | website= math.ucr.edu |access-date=2008-11-09}}</ref> Together they are ranked by many scientists as the second-largest of the five major extinctions in Earth's history in terms of percentage of [[genus|genera]] that became extinct.
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In May&nbsp;2020, studies suggested that the causes of the mass extinction were [[global warming]], related to [[volcanism]], and [[Hypoxia (environmental)|anoxia]], and not, as considered earlier, cooling and [[glaciation]].<ref name="NYT-20200610">{{cite news | vauthors = Hall S |date=10 June 2020 |title=Familiar culprit may have caused mysterious mass extinction – A planet heated by giant volcanic eruptions drove the earliest known wipeout of life on Earth |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2020/06/10/science/global-warming-ordovician-extinction.html |access-date=15 June 2020 }}</ref><ref name=GEO-20200518>{{cite journal | vauthors = Bond DP, Grasby SE |date=18 May 2020 |title=Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation |journal= Geology |volume=48 |issue=8 |pages=777–781 |doi=10.1130/G47377.1 |bibcode=2020Geo....48..777B |s2cid=234740291|doi-access=free }}</ref> However, this is at odds with numerous previous studies, which have indicated global cooling as the primary driver.<ref>{{cite journal | vauthors = Harper DA, Hammarlund EU, Rasmussen CM |title=End Ordovician extinctions: A coincidence of causes |journal=Gondwana Research |date=May 2014 |volume=25 |issue=4 |pages=1294–1307 |doi= 10.1016/j.gr.2012.12.021|bibcode=2014GondR..25.1294H |url=https://durham-repository.worktribe.com/output/1498236 }}</ref> Most recently, the deposition of volcanic ash has been suggested to be the trigger for reductions in atmospheric carbon dioxide leading to the glaciation and anoxia observed in the geological record.<ref>{{cite journal | vauthors = Longman J, Mills BJ, Manners HR, Gernon TM, Palmer MR |title=Late Ordovician climate change and extinctions driven by elevated volcanic nutrient supply |journal=Nature Geoscience |date=December 2021 |volume=14 |issue=12 |pages=924–929 |doi=10.1038/s41561-021-00855-5 |bibcode=2021NatGe..14..924L |s2cid=244803446 |url= https://eprints.soton.ac.uk/452002/1/34044_3_merged_1630656585.pdf }}</ref>
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|style="vertical-align:top;text-align:center;" rowspan="2"| {{big|'''{{math|2}}'''}}
|style="vertical-align:top;text-align:left;"| '''[[Late Devonian mass extinction]]'''
|style="vertical-align:top;text-align:left;"| 372–359&nbsp;[[Megaannum|Ma]]
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|style="vertical-align:top;text-align:left;" colspan="3"| The [[Late Devonian mass extinction|Late Devonian extinctions]] were a series of events that occupied much of the [[Late Devonian]] up to the [[Devonian]]–[[Carboniferous]] transition. The Late Devonian was an interval of high diversity loss, concentrated into two extinction events. Scientists have linked both events to anoxic conditions in the water.
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The larger extinction was the [[Kellwasser event|Kellwasser Event]] ([[Frasnian]]-[[Famennian]], or F-F, 372&nbsp;Ma), an extinction event at the end of the Frasnian, about midway through the Late Devonian. This extinction annihilated [[coral reef]]s and numerous tropical [[Benthic zone|benthic]] (seabed-living) animals such as jawless fish, [[brachiopod]]s, and [[trilobite]]s. Many scientists believe that the Kellwasser event resulted from land nutrients being carried into the ocean by rivers. These nutrients caused massive algal blooms. As the algae died and decomposed, they consumed dissolved oxygen in the water column, leading to anoxic conditions which eventually caused the extinctions.

The other major piece of the Devonian extinction was the [[Hangenberg event|Hangenberg Event]] (Devonian-Carboniferous, or D-C, 359&nbsp;Ma), which brought an end to the Devonian as a whole. This extinction wiped out the armored [[placoderm]] fish and nearly led to the extinction of the newly evolved [[ammonoids]]. 
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Together, the Kellwasser event and the Hangenberg event eliminated about 19% of all families, 50% of all [[genera]]<ref name=ucr/> and at least 70% of all species.<ref>{{cite book | vauthors = Briggs D, Crowther PR |year = 2008 |title = Palaeobiology |volume=II |page = 223 |publisher = John Wiley & Sons |isbn = 978-0-470-99928-8 |url = https://books.google.com/books?id=lBH2BM7uZL8C |via=Google Books}}</ref> Sepkoski and Raup (1982)<ref name=Raup/> did not initially consider the Late Devonian extinction interval ([[Givetian]], Frasnian, and Famennian stages) to be statistically significant.<ref name=Raup/> Regardless, later studies have affirmed the strong ecological impacts of the Kellwasser and Hangenberg Events.<ref name=McGhee_2013/>
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|style="vertical-align:top;text-align:center;" rowspan="2"| {{big|'''{{math|3}}'''}}
|style="vertical-align:top;text-align:left;"| '''[[Permian–Triassic extinction event]]'''
|style="vertical-align:top;text-align:left;"| 252&nbsp;[[Megaannum|Ma]]
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|style="vertical-align:top;text-align:left;" colspan="3"| [[File:Kainops invius lateral and ventral.JPG|thumb|[[Trilobites]] were highly successful marine animals until the Permian–Triassic extinction event wiped them all out.]]
The End Permian extinction or the "Great Dying" occurred at the [[Permian]]–[[Triassic]] transition.<ref name=NYT-20170216>{{cite news |vauthors = St Fleur N |title=After Earth's worst mass extinction, life rebounded rapidly, fossils suggest |url=https://www.nytimes.com/2017/02/16/science/great-dying-permian-extinction-fossils.html |archive-url= https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2017/02/16/science/great-dying-permian-extinction-fossils.html |archive-date=2022-01-01 |url-access=limited |newspaper= The New York Times |date=16 February 2017 |access-date=17 February 2017 }}{{cbignore}}</ref> It was the Phanerozoic Eon's largest extinction: 53% of marine families died, 84% of marine genera, about 81% of all marine species<ref name=Stanley_2016/> and an estimated 70% of terrestrial vertebrate species.<ref name=Erwin1994>{{cite journal |last=Erwin |first=Douglas H. |date=20 January 1994 |title=The Permo-Triassic extinction |journal=Nature |volume= 367 |issue=6460 |page=231 |doi=10.1038/367231a0|bibcode=1994Natur.367..231E |s2cid=4328753 }}</ref> This is also the largest known extinction event for [[insect]]s.<ref name=Labandeira>{{cite journal | vauthors = Labandeira CC, Sepkoski JJ | title = Insect diversity in the fossil record | journal = Science | volume = 261 | issue = 5119 | pages = 310–315 | date = July 1993 | pmid = 11536548 | doi = 10.1126/science.11536548 | citeseerx = 10.1.1.496.1576 | bibcode = 1993Sci...261..310L | hdl = 10088/6563 }}</ref> The highly successful marine arthropod the [[trilobite]] became extinct. The evidence regarding plants is less clear, but new taxa became dominant after the extinction.<ref name=McElwain2007>{{cite journal | vauthors = McElwain JC, Punyasena SW | title = Mass extinction events and the plant fossil record | journal = Trends in Ecology & Evolution | volume = 22 | issue = 10 | pages = 548–557 | date = October 2007 | pmid = 17919771 | doi = 10.1016/j.tree.2007.09.003 | bibcode = 2007TEcoE..22..548M }}</ref>
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The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of early [[synapsid]]s. The recovery of vertebrates took 30&nbsp;million years,<ref>{{cite journal | vauthors = Sahney S, Benton MJ | title = Recovery from the most profound mass extinction of all time | journal = Proceedings. Biological Sciences | volume = 275 | issue = 1636 | pages = 759–765 | date = April 2008 | pmid = 18198148 | pmc = 2596898 | doi = 10.1098/rspb.2007.1370 | author-link2 = Michael Benton }}</ref> but the vacant [[ecological niche|niches]] created the opportunity for [[archosaur]]s to become ascendant. In the seas, the percentage of animals that were [[sessility (motility)|sessile]] (unable to move about) dropped from 67% to 50%. The whole late Permian was a difficult time, at least for marine life, even before the P–T boundary extinction. More recent research has indicated that the [[End-Capitanian extinction event]] that preceded the "Great Dying" likely constitutes a separate event from the P–T extinction; if so, it would be larger than some of the "Big Five" extinction events.
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|style="vertical-align:top;text-align:center;" rowspan="2"| {{big|'''{{math|4}}'''}}
|style="vertical-align:top;text-align:left;"| '''[[Triassic–Jurassic extinction event]]'''
|style="vertical-align:top;text-align:left;"| 201.3&nbsp;[[Megaannum|Ma]]
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|style="vertical-align:top;text-align:left;" colspan="3"| The End Triassic extinction marks the [[Triassic]]–[[Jurassic]] transition. About 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species became extinct.<ref name=ucr/> Most non-dinosaurian [[archosaur]]s, most [[therapsid]]s, and most of the large [[amphibian]]s were eliminated, leaving [[dinosaur]]s with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while [[Diapsid#Taxonomy|non-archosaurian diapsids]] continued to dominate marine environments. The [[Temnospondyl]] lineage of large amphibians also survived until the Cretaceous in Australia (such as ''[[Koolasuchus]]'').
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|style="vertical-align:top;text-align:center;" rowspan="2"| {{big|'''{{math|5}}'''}}
|style="vertical-align:top;text-align:left;"| '''[[Cretaceous–Paleogene extinction event]]'''
|style="vertical-align:top;text-align:left;"| {{period start|Paleogene}}&nbsp;[[Megaannum|Ma]]
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|style="vertical-align:top;text-align:left;" colspan="3"| [[Image:KT boundary 054.jpg|thumb|[[Badlands]] near [[Drumheller]], [[Alberta]], where erosion has exposed the [[Cretaceous–Paleogene boundary]].]]
The End Cretaceous extinction, or the K–Pg extinction (formerly K–T extinction) occurred at the [[Cretaceous]] ([[Maastrichtian]]) – [[Paleogene]] ([[Danian]]) transition.<ref>{{cite journal | vauthors = Macleod N, Rawson PF, Forey P, Banner F, Boudagher-Fadel M, Bown P, Burnett J, Chambers P, Culver S, Evans S, Jeffery C, Kaminski M, Lord A, Milner A, Milner A, Morris N, Owen E, Rosen B, Smith A, Taylor P, Urquhart E, Young J | display-authors = 6 |date=April 1997 |title=The Cretaceous-Tertiary biotic transition |journal=Journal of the Geological Society |volume=154 |issue=2 |pages=265–92 |doi=10.1144/gsjgs.154.2.0265 |bibcode= 1997JGSoc.154..265M |s2cid=129654916 }}</ref> The event was formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary; it is now officially named the Cretaceous–Paleogene (or K–Pg) extinction event.
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About 17% of all families, 50% of all [[genera]]<ref name=ucr/> and 75% of all species became extinct.<ref name=Raup>{{cite journal | vauthors = Raup DM, Sepkoski JJ| date = March 1982  | title = Mass extinctions in the marine fossil record | journal = Science | volume = 215 | issue = 4539 | pages = 1501–1503 | pmid = 17788674 | doi = 10.1126/science.215.4539.1501 | s2cid = 43002817 | bibcode = 1982Sci...215.1501R }}</ref> In the seas all the [[Ammonoidea|ammonites]], [[Sauropterygia|plesiosaurs]] and [[mosasaur]]s disappeared and the percentage of [[Sessility (zoology)|sessile]] animals was reduced to about 33%. All known non-avian [[dinosaur]]s became extinct during that time.<ref>{{cite journal |vauthors=Fastovsky DE, Sheehan PM |year=2005 |title=The extinction of the dinosaurs in North America |journal=GSA Today |volume=15 |issue=3 |pages=4–10 |doi=10.1130/1052-5173(2005)15<4:TEOTDI>2.0.CO;2 |bibcode=2005GSAT...15c...4F }}</ref> The boundary event was severe with a significant amount of variability in the rate of extinction between and among different [[clade]]s. [[Mammal]]s, descended from the [[synapsid]]s, and [[bird]]s, a side-branch of the [[theropod]] dinosaurs, emerged as the two predominant clades of terrestrial tetrapods.
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[[File:Phanerozoic Biodiversity.svg|thumb|300px|Declines in the numbers of terrestrial and aquatic [[Genus|genera]] at times of extinction events.]]
Despite the common presentation focusing only on these five events, no measure of extinction shows any definite line separating them from the many other [[Phanerozoic]] extinction events that appear only slightly lesser catastrophes; further, using different methods of calculating an extinction's impact can lead to other events featuring in the top five.<ref name=McGhee2011>{{cite journal | vauthors = McGhee GR, Sheehan PM, Bottjer DJ, Droser ML | year = 2011 | title = Ecological ranking of Phanerozoic biodiversity crises: The Serpukhovian (early Carboniferous) crisis had a greater ecological impact than the end-Ordovician | doi = 10.1130/G32679.1 | journal = Geology | volume = 40 | issue = 2 | pages = 147–50 |bibcode = 2012Geo....40..147M }}</ref>

Fossil records of older events are more difficult to interpret. This is because:
* Older fossils are more difficult to find, as they are usually buried at a considerable depth.
* Dating of older fossils is more difficult.
* Productive fossil beds are researched more than unproductive ones, therefore leaving certain periods unresearched.
* Prehistoric environmental events can disturb the [[Deposition (sediment)|deposition]] process.
* Marine fossils tend to be better preserved than their more sought-after land-based counterparts, but the deposition and preservation of fossils on land is more erratic.<ref name=sole>{{cite book | vauthors = Sole RV, Newman M |year=2003 |chapter= Extinctions and biodiversity in the fossil record | veditors = Mooney HA, Canadell JG |title=Encyclopedia of Global Environmental Change |volume=2: The Earth System: Biological and ecological dimensions of global environmental change |pages=297–391 |publisher=Wiley |isbn=978-0-470-85361-0 }}</ref>

It has been suggested that the apparent variations in marine biodiversity may actually be an artifact, with abundance estimates directly related to quantity of rock available for sampling from different time periods.<ref>{{cite journal | vauthors = Smith AB, McGowan AJ | date = December 2005 | title = Cyclicity in the fossil record mirrors rock outcrop area | journal = Biology Letters | volume = 1 | issue = 4 | pages = 443–445 | pmid = 17148228 | pmc = 1626379 | doi = 10.1098/rsbl.2005.0345 }}</ref> However, statistical analysis shows that this can only account for 50% of the observed pattern,{{Citation needed|date=July 2007}} and other evidence such as fungal spikes (geologically rapid increase in [[Fungus|fungal]] abundance) provides reassurance that most widely accepted extinction events are real. A quantification of the rock exposure of Western Europe indicates that many of the minor events for which a biological explanation has been sought are most readily explained by [[sampling bias]].<ref name="Smith2007">{{cite journal | vauthors = Smith AB, McGowan AJ | year = 2007 | title = The shape of the Phanerozoic marine palaeodiversity curve: How much can be predicted from the sedimentary rock record of Western Europe? | journal = Palaeontology | volume = 50 | issue = 4 | pages = 765–74 | doi = 10.1111/j.1475-4983.2007.00693.x | bibcode = 2007Palgy..50..765S | s2cid = 55728929 }}</ref>

== Sixth mass extinction ==
{{Main|Holocene extinction|Biodiversity loss}}
Research completed after the seminal 1982 paper (Sepkoski and Raup) has concluded that a sixth mass extinction event due to human activities is currently underway:
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{|
|-
|style="vertical-align:top;text-align:center;width:2%;" rowspan="2"| {{big|'''{{math|6}}'''}}
|style="vertical-align:top;text-align:left;;width:35%;"| '''[[Holocene extinction]]'''
|style="vertical-align:top;text-align:left;"| currently ongoing
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|style="vertical-align:top;text-align:left;" colspan="3"| Extinctions have occurred at over 1,000&nbsp;times the [[background extinction rate]] since 1900, and the rate is increasing.<ref name=McCallum-2015-05-27>{{cite journal | vauthors = McCallum ML |title=Vertebrate biodiversity losses point to a sixth mass extinction |journal=Biodiversity and Conservation |date=27 May 2015 |volume=24 |issue=10 |pages=2497–2519 |doi=10.1007/s10531-015-0940-6 |bibcode=2015BiCon..24.2497M |s2cid=16845698 }}</ref><ref name=Pimm-Jenkins-etal-2014-05-29>{{cite journal | vauthors = Pimm SL, Jenkins CN, Abell R, Brooks TM, Gittleman JL, Joppa LN, Raven PH, Roberts CM, Sexton JO | display-authors = 6 | title = The biodiversity of species and their rates of extinction, distribution, and protection | journal = Science | volume = 344 | issue = 6187 | pages = 1246752 | date = May 2014 | pmid = 24876501 | doi = 10.1126/science.1246752 | s2cid = 206552746 }}</ref>{{efn|Biodiversity is declining faster than at any time in human history. Current extinction rates, for example, are around 100~1,000&nbsp;times higher than the baseline rate, and they are increasing.<ref name=Dasgupta-2021>{{cite web | vauthors = Dasgupta P |author-link= Partha Dasgupta |date=2021 |title=The Economics of biodiversity |website=The Dasgupta Review Headline Messages |publisher= UK government | page=1 |url= https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/957629/Dasgupta_Review_-_Headline_Messages.pdf |access-date= January 9, 2022 }}</ref>}} The mass extinction is a result of [[Human impact on the environment|human activity]] (an [[ecocide]])<ref name=MacDonald-2015-07-03>{{cite news | vauthors = MacDonald J  |date=3 July 2015 |title=It's official: A global mass extinction is under way  |website=JSTOR Daily |url= https://daily.jstor.org/its-official-a-global-mass-extinction-is-under-way/ }}</ref><ref name=Grennan-2015-06-24>{{cite news | vauthors = Grennan M |date=June 24, 2015 |title=We're entering a sixth mass extinction, and it's our fault |magazine=[[Popular Science]] |url=https://www.popsci.com/were-entering-sixth-mass-extinction-and-its-our-fault/}}</ref><ref name=Sutter/><ref name=Cowie-Bouchet-Fontaine-2022>{{cite journal | vauthors = Cowie RH, Bouchet P, Fontaine B | date = April 2022 | title = The sixth mass extinction: Fact, fiction or speculation? | journal = Biological Reviews of the Cambridge Philosophical Society | volume = 97 | issue = 2 | pages = 640–663 | pmid = 35014169 | doi = 10.1111/brv.12816 | pmc = 9786292 | doi-access = free | orig-date = 10 January 2022 | type = online preprint }}</ref> driven by [[population growth]] and [[overconsumption]] of the earth's natural resources.{{efn|"The ongoing sixth mass extinction may be the most serious environmental threat to the persistence of civilization, because it is irreversible. Thousands of populations of critically endangered vertebrate animal species have been lost in a century, indicating that the sixth mass extinction is human caused and accelerating. The acceleration of the extinction crisis is certain because of the still fast growth in human numbers and {{nobr|consumption rates." — Ceballos, Ehrlich, & Raven (2020)<ref name=Ceballos-Ehrlich-Raven-2020>{{cite journal | vauthors = Ceballos G, Ehrlich PR, Raven PH | date = June 2020 | title = Vertebrates on the brink as indicators of biological annihilation and the sixth mass extinction | journal =  Proceedings of the National Academy of Sciences| volume = 117 | issue = 24 | pages = 13596–13602 | pmid = 32482862 | pmc = 7306750 | doi = 10.1073/pnas.1922686117 | doi-access = free | bibcode = 2020PNAS..11713596C }}</ref>}}}} The 2019 [[Global Assessment Report on Biodiversity and Ecosystem Services|global biodiversity assessment]] by [[IPBES]] asserts that out of an estimated 8&nbsp;million species, 1&nbsp;million plant and animal species are currently threatened with extinction.<ref name="Global Assessment">{{cite conference |vauthors = Brondizio ES, Settele J, Díaz S, Ngo HT |collaboration=Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services |date=25 November 2019 |title=Summary for policymakers of the global assessment report on biodiversity and ecosystem services |series=IPBES plenary seventh session |conference=Intergovernmental Science-Policy Platform on Biodiversity Ecosystem Services |isbn=978-3-947851-13-3 |doi=10.5281/zenodo.3553579}}</ref><ref name=Watts-2019-05-06-Gdn>{{cite news | vauthors = Watts J |date=6 May 2019 |title=Human society under urgent threat from loss of Earth's natural life |newspaper=[[The Guardian]] |place=London |url= https://www.theguardian.com/environment/2019/may/06/human-society-under-urgent-threat-loss-earth-natural-life-un-report |access-date=May 10, 2019}}</ref><ref name=Plumer-2019-05-06-NYT>{{cite news | vauthors = Plumer B |date=6 May 2019 |title=Humans are speeding extinction and altering the natural world at an 'unprecedented' pace |newspaper=[[The New York Times]] |url= https://www.nytimes.com/2019/05/06/climate/biodiversity-extinction-united-nations.html |url-access=limited |access-date=May 10, 2019 |archive-url= https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2019/05/06/climate/biodiversity-extinction-united-nations.html |archive-date=2022-01-01 }}{{cbignore}}</ref><ref name=IPBES-2019-05-06-PR>{{cite press release |title=Nature's dangerous decline 'unprecedented'; species extinction rates 'accelerating' |date= 6 May 2019 |website=[[Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services]] |url=https://www.ipbes.net/news/Media-Release-Global-Assessment |access-date=10 May 2019 }}</ref> In late 2021, [[World Wide Fund for Nature|WWF]] Germany suggested that over a million species could go extinct within a decade in the "largest mass extinction event since the end of the dinosaur age."<ref name=DW-2021-12-21-WWF>{{cite news |title=Looming mass extinction could be biggest 'since the dinosaurs,' says WWF |date=29 December 2021 |website=[[Deutsche Welle]] |location=Germany |url= https://www.dw.com/en/looming-mass-extinction-could-be-biggest-since-the-dinosaurs-says-wwf/a-60289286 |access-date=January 3, 2022}}</ref> A 2023 study published in ''[[PNAS]]'' concluded that at least 73 genera of animals have gone extinct since 1500. If humans had never existed, it would have taken 18,000&nbsp;years for the same genera to have disappeared naturally, the report states.<ref name=Rozsa-2023-09-19-Sln>{{cite news |last=Rozsa |first=Matthew |date=19 September 2023 |title=Experts warn of a "biological holocaust" as human-caused extinction "mutilates" the tree of life |website=[[Salon.com]] |url=https://www.salon.com/2023/09/19/experts-warn-of-a-biological-holocaust-as-human-caused-extinction-mutilates-the-tree-of-life/ |access-date= September 21, 2023}}</ref><ref name=Ceballos-Ehrlich-2023>{{cite journal |last1=Ceballos |first1=Gerardo |last2=Ehrlich |first2=Paul R. |date=2023 |title= Mutilation of the tree of life via mass extinction of animal genera |journal= Proceedings of the National Academy of Sciences |volume=120 |issue=39 |page= e2306987120 |doi=10.1073/pnas.2306987120 |doi-access=free |pmid=37722053 |pmc=10523489 |bibcode=2023PNAS..12006987C }}</ref><ref name=Grnfld-2023-09-19-Gdn>{{cite news |last= Greenfield |first=Patrick |date=September 19, 2023 |title='Mutilating the tree of life': Wildlife loss accelerating, scientists warn |department= Environment |newspaper= The Guardian |location=London |url=https://www.theguardian.com/environment/2023/sep/19/mutilating-the-tree-of-life-wildlife-loss-accelerating-scientists-warn |access-date=September 21, 2023}}</ref>
|}

== Extinctions by severity ==
{{Main|List of extinction events}}

Extinction events can be tracked by several methods, including geological change, ecological impact, extinction vs. origination ([[speciation]]) rates, and most commonly diversity loss among [[Taxonomy|taxonomic]] units. Most early papers used [[Family (biology)|families]] as the unit of taxonomy, based on compendiums of marine animal families by [[Jack Sepkoski|Sepkoski]] (1982, 1992).<ref name="Sepkoski_1982" /><ref name="Sepkoski_1992" /> Later papers by Sepkoski and other authors switched to [[genera]], which are more precise than families and less prone to taxonomic bias or incomplete sampling relative to species.<ref name="Sepkoski_2002" /> These are several major papers estimating loss or ecological impact from fifteen commonly-discussed extinction events. Different methods used by these papers are described in the following section. The "Big Five" mass extinctions are bolded.
{| class="wikitable sortable" style="text-align: center;"
|+Extinction proportions (diversity loss) of marine genera or ecological impact in estimates of mass extinction severity
!rowspan=2|Extinction name
!rowspan=2|Age<br>([[Myr|Ma]])
!rowspan=2|Sepkoski (1996)<ref name="Sepkoski_1996" /><br>Multiple-interval<br>genera
!rowspan=2|Bambach<br>(2006)<ref name="Bambach_2006" />
!colspan=2|McGhee ''et al''. (2013)<ref name="McGhee_2013" />
!rowspan=2|Stanley (2016)<ref name="Stanley_2016" />
|-
!Taxonomic<br>loss
!Ecological<br>ranking
|-
|'''[[Late Ordovician mass extinction|Late Ordovician]] ([[Ashgill (age)|Ashgillian]] / [[Hirnantian]])'''
|445–444
|~49%
|57%{{ref label|total|d|d}}<br>(40%, 31%){{ref label|2pulse|e|e}}
|52%
|7
|42–46%
|-
|[[Lau event]] ([[Ludfordian]])
|424
|~23%
| –
|9%
|9
| –
|-
|[[Kačák Event]] ([[Eifelian]])
|388~
|~24%{{ref label|Sepgraph|a|a}}
| –
|32%
|9
| –
|-
|[[Taghanic Event]] ([[Givetian]])
|384~
|~30%{{ref label|Sepgraph|a|a}}
|28.5%
|36%
|8
| –
|-
|'''[[Late Devonian extinction|Late Devonian]]/[[Kellwasser event]] ([[Frasnian]])'''
|372
|~35%
|34.7%
|40%
|4
|16–20%
|-
|End-Devonian/[[Hangenberg event]] ([[Famennian]])
|359
|~28%{{ref label|Sepgraph|a|a}}
|31%
|50%
|7
|<13%{{ref label|noS16|f|f}}
|-
|[[Serpukhovian#Serpukhovian extinction|Serpukhovian]]
|330–325~
|~23%
|31%
|39%
|6
|13–15%
|-
|[[Capitanian mass extinction event|Capitanian]]
|260
|~47%{{ref label|Cap|b|b}}
|48%
|25%
|5
|33–35%
|-
|'''[[Permian–Triassic extinction event|Permian–Triassic]] ([[Changhsingian]])'''
|252
|~58%
|55.7%
|83%
|1
|62%
|-
|'''[[Triassic–Jurassic extinction event|Triassic–Jurassic]] ([[Rhaetian]])'''
|201
|~37%{{ref label|Norian|c|c}}
|47%{{ref label|Norian|c|c}}
|73%
|3
|N/A{{ref label|timing|g|g}}
|-
|[[Toarcian Oceanic Anoxic Event|Pliensbachian-Toarcian]]
|186–178
|~14%
|25%, 20%{{ref label|2pulse|e|e}}
| –
| –
| –
|-
|[[Tithonian#Tithonian extinction|End-Jurassic]] (Tithonian)
|145
|~18%
|20%
| –
| –
| –
|-
|[[Cenomanian-Turonian boundary event|Cenomanian-Turonian]]
|94
|~15%
|25%
| –
| –
| –
|-
|'''[[Cretaceous–Paleogene extinction event|Cretaceous–Paleogene]] ([[Maastrichtian]])'''
|66
|~39%
|40–47%
|40%
|2
|38–40%
|-
|[[Eocene–Oligocene extinction event|Eocene–Oligocene]]
|34
|~11%
|15.6%
| –
| –
| –
|}
{{note label|Sepgraph|a|a}} Graphed but not discussed by Sepkoski (1996), considered continuous with the Late Devonian mass extinction<br>{{note label|Cap|b|b}} At the time considered continuous with the end-Permian mass extinction<br>{{note label|Norian|c|c}} Includes late [[Norian]] time slices<br>{{note label|total|d|d}} Diversity loss of both pulses calculated together<br>{{note label|2pulse|e|e}} Pulses extend over adjacent time slices, calculated separately<br>{{note label|noS16|f|f}} Considered ecologically significant, but not analyzed directly<br>{{note label|timing|g|g}} Excluded due to a lack of consensus on Late Triassic chronology

== The study of major extinction events ==

=== Breakthrough studies in the 1980s–1990s ===
[[File:LWA with Walt.JPG|thumb|[[Luis Walter Alvarez|Luis]] (left) and [[Walter Alvarez]] (right) at the [[Cretaceous–Paleogene boundary|K-Pg boundary]] in [[Gubbio, Italy]] in 1981. This team discovered geological evidence for an asteroid impact causing the K-Pg extinction, spurring a wave of public and scientific interest in mass extinctions and their causes]]
For much of the 20th century, the study of mass extinctions was hampered by insufficient data. Mass extinctions, though acknowledged, were considered mysterious exceptions to the prevailing [[Gradualism|gradualistic]] view of prehistory, where slow evolutionary trends define faunal changes. The first breakthrough was published in 1980 by a team led by [[Luis Walter Alvarez|Luis Alvarez]], who discovered trace metal evidence for an [[Impact event|asteroid impact]] at the end of the [[Cretaceous]] period. The [[Alvarez hypothesis]] for the [[End-Cretaceous extinction event|end-Cretaceous extinction]] gave mass extinctions, and [[Catastrophism#Current application|catastrophic]] explanations, newfound popular and scientific attention.<ref name="Alvarez">{{cite journal | vauthors = Alvarez LW, Alvarez W, Asaro F, Michel HV | date = June 1980 | title = Extraterrestrial cause for the cretaceous-tertiary extinction | journal = Science | volume = 208 | issue = 4448 | pages = 1095–1108 | pmid = 17783054 | doi = 10.1126/science.208.4448.1095 | bibcode = 1980Sci...208.1095A | s2cid = 16017767 | citeseerx = 10.1.1.126.8496 }}</ref>
[[File:Sepkoski 1997 extinction graphs.png|left|thumb|upright=1.4|Changes in diversity among genera and families, according to Sepkoski (1997). The "Big Five" mass extinctions are labelled with arrows, and taxa are segregated into Cambrian- (Cm), Paleozoic- (Pz), and Modern- (Md) type faunas.]]
Another landmark study came in 1982, when a paper written by [[David M. Raup]] and [[Jack Sepkoski]] was published in the journal ''[[Science (journal)|Science]]''.<ref name=Raup/> This paper, originating from a compendium of extinct marine animal [[Family (biology)|families]] developed by Sepkoski,<ref name=Sepkoski_1982>{{cite report |author=Sepkoski, J.J. Jr. |year=1982 |title=A compendium of fossil marine families |series=Milwaukee Public Museum Contributions in Biology and Geology |volume=51 |pages=1–125 |url=https://www.mpm.edu/sites/default/files/files%20and%20dox/C%26R/library/bio-geo/%23051%20MPM%20Contributions%20in%20Biology%20and%20Geology%20Number%2051.pdf }}</ref> identified five peaks of marine family extinctions that stand out among a backdrop of decreasing extinction rates through time. Four of these peaks were statistically significant: the [[Ashgillian]] ([[End-Ordovician extinction event|end-Ordovician]]), [[Late Permian]], [[Norian]] ([[End-Triassic extinction|end-Triassic]]), and [[Maastrichtian]] (end-Cretaceous). The remaining peak was a broad interval of high extinction smeared over the later half of the [[Devonian]], with its apex in the [[Frasnian]] stage.<ref name="Raup" />

Through the 1980s, Raup and Sepkoski continued to elaborate and build upon their extinction and origination data, defining a high-resolution [[biodiversity]] curve (the "Sepkoski curve") and successive [[evolutionary fauna]]s with their own patterns of diversification and extinction.<ref>{{Cite journal | author = Sepkoski, J.J. Jr. |year=1981 |title=A factor analytic description of the Phanerozoic marine fossil record |journal=Paleobiology |language=en |volume=7 |issue=1 |pages=36–53 |doi=10.1017/S0094837300003778 |bibcode=1981Pbio....7...36S |s2cid=133114885 |issn=0094-8373 |url=https://websites.pmc.ucsc.edu/~pkoch/EART_206/09-0120/Supplemental/Sepkoski%2081%20Pbio%207-36.pdf}}</ref><ref>{{cite journal | vauthors = Sepkoski JJ, Bambach RK, Raup DM, Valentine JW |year=1981 |title=Phanerozoic marine diversity and the fossil record |journal=Nature |language=en |volume=293 |issue=5832 |pages=435–437 |doi=10.1038/293435a0 |bibcode=1981Natur.293..435S |s2cid=4282371 |issn=1476-4687 |url= http://www.tomwbell.net/uploads/5/6/9/7/56976837/293435a0__1_.pdf}}</ref><ref>{{Cite book | vauthors = Sepkoski JJ |title=Geological Implications of Impacts of Large Asteroids and Comets on the Earth |date=1982-01-01 |chapter=Mass extinctions in the Phanerozoic oceans: A review |publisher=Geological Society of America |series=Geological Society of America Special Papers |volume=190 |pages=283–290 |language=en |id=Special Paper 190 |doi=10.1130/SPE190-p283 |isbn=0-8137-2190-3  |chapter-url=https://pubs.geoscienceworld.org/gsa/books/book/350/chapter/3796461/Mass-extinctions-in-the-Phanerozoic-oceans-A}}</ref><ref>{{Cite journal | vauthors = Sepkoski JJ |year=1984 |title=A kinetic model of Phanerozoic taxonomic diversity. III. Post-Paleozoic families and mass extinctions |journal=Paleobiology |language=en |volume=10 |issue=2 |pages=246–267 |doi=10.1017/S0094837300008186 |bibcode=1984Pbio...10..246S |s2cid=85595559 |issn=0094-8373 |url=https://www.cambridge.org/core/product/identifier/S0094837300008186/type/journal_article|url-access=subscription }}</ref><ref name=Sepkoski_1986>{{cite book | vauthors = Sepkoski JJ |year=1986 | chapter = Phanerozoic overview of mass extinction | title = Patterns and Processes in the History of Life |series=Dahlem Workshop Reports |pages=277–295 | veditors = Raup DM, Jablonski D |place=Berlin & Heidelberg, DE |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-642-70831-2_15 |isbn=978-3-642-70833-6 | chapter-url=http://link.springer.com/10.1007/978-3-642-70831-2_15 |access-date=2022-08-14 }}</ref><ref>{{cite journal | vauthors = Sepkoski JJ | year = 1989 | title = Periodicity in extinction and the problem of catastrophism in the history of life | journal = Journal of the Geological Society | volume = 146 | issue = 1 | pages = 7–19 | pmid = 11539792 | doi = 10.1144/gsjgs.146.1.0007 | bibcode = 1989JGSoc.146....7S | s2cid = 45567004 }}</ref> Though these interpretations formed a strong basis for subsequent studies of mass extinctions, Raup and Sepkoski also proposed a more controversial idea in 1984: a 26-million-year periodic pattern to mass extinctions.<ref name=Raup1984/> Two teams of [[astronomer]]s linked this to a hypothetical [[brown dwarf]] in the distant reaches of the [[Solar System]], inventing the "[[Nemesis hypothesis]]", which has been strongly disputed by other astronomers.

Around the same time, Sepkoski began to devise a compendium of marine animal [[genera]], which would allow researchers to explore extinction at a finer taxonomic resolution. He began to publish preliminary results of this in-progress study as early as 1986, in a paper that identified 29 extinction intervals of note.<ref name=Sepkoski_1986/> By 1992, he also updated his 1982 family compendium, finding minimal changes to the diversity curve despite a decade of new data.<ref name="Sepkoski_1992">{{cite report | vauthors = Sepkoski Jr JJ |year=1992 |title=A compendium of fossil marine animal families |edition=2nd |series=Milwaukee Public Museum Contributions in Biology and Geology |volume=83 |pages=1–156 |pmid=11542296 |url=https://www.mpm.edu/sites/default/files/files%20and%20dox/C%26R/library/bio-geo/%23083%20MPM%20Contributions%20in%20Biology%20and%20Geology%20Number%2083.pdf }}</ref><ref>{{cite journal | vauthors = Sepkoski JJ | year = 1993 | title = Ten years in the library: New data confirm paleontological patterns | journal = Paleobiology | volume = 19 | issue = 1 | pages = 43–51 | pmid = 11538041 | doi = 10.1017/S0094837300012306 | bibcode = 1993Pbio...19...43S | s2cid = 44295283 }}</ref> In 1996, Sepkoski published another paper that tracked marine genera extinction (in terms of net diversity loss) by stage, similar to his previous work on family extinctions. The paper filtered its sample in three ways: all genera (the entire unfiltered sample size), multiple-interval genera (only those found in more than one stage), and "well-preserved" genera (excluding those from groups with poor or understudied fossil records). Diversity trends in marine animal families were also revised based on his 1992 update.<ref name="Sepkoski_1996">{{cite book | vauthors = Sepkoski JJ |chapter=Patterns of Phanerozoic Extinction: A Perspective from Global Data Bases |year=1996 |title = Global Events and Event Stratigraphy in the Phanerozoic |pages=35–51 | veditors = Walliser OH |place=Berlin & Heidelberg, DE |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-642-79634-0_4 |isbn=978-3-642-79636-4 | chapter-url=http://link.springer.com/10.1007/978-3-642-79634-0_4 |access-date=2022-08-14}}</ref>

Revived interest in mass extinctions led many other authors to re-evaluate geological events in the context of their effects on life.<ref>{{cite journal | vauthors = Jablonski D | date = August 1991 | title = Extinctions: A paleontological perspective | journal = Science | volume = 253 | issue = 5021 | pages = 754–757 | pmid = 17835491 | doi = 10.1126/science.253.5021.754 | bibcode = 1991Sci...253..754J }}</ref> A 1995 paper by [[Michael Benton]] tracked extinction and origination rates among both marine and continental (freshwater & terrestrial) families, identifying 22 extinction intervals and no periodic pattern.<ref>{{cite journal | vauthors = Benton MJ | date = April 1995 | title = Diversification and extinction in the history of life | journal = Science | volume = 268 | issue = 5207 | pages = 52–58 | pmid = 7701342 | doi = 10.1126/science.7701342 | bibcode = 1995Sci...268...52B | url = http://doc.rero.ch/record/14806/files/PAL_E1962.pdf }}</ref> Overview books by O.H. Walliser (1996) and [[Anthony Hallam|A. Hallam]] and P.B. Wignall (1997) summarized the new extinction research of the previous two decades.<ref>{{Cite book | veditors = Walliser OH |year=1996 |title=Global Events and Event Stratigraphy in the Phanerozoic: Results of the International Interdisciplinary Cooperation in the IGCP-Project 216 "Global Biological Events in Earth History" |publisher=Springer Berlin Heidelberg |isbn=978-3-642-79636-4 |location=Berlin, Heidelberg |language=en |doi=10.1007/978-3-642-79634-0 |url=http://link.springer.com/10.1007/978-3-642-79634-0}}</ref><ref>{{Cite book | vauthors = Hallam A, Wignall PB |title=Mass Extinctions and Their Aftermath  |publisher=Oxford University Press |year=1997 |location=Oxford}}</ref> One chapter in the former source lists over 60 geological events that could conceivably be considered global extinctions of varying sizes.<ref>{{cite book | vauthors = Barnes CR, Hallam A, Kaljo D, Kauffman EG, Walliser OH |year=1996 | chapter = Global Event Stratigraphy |title = Global Events and Event Stratigraphy in the Phanerozoic |pages=319–333 |place=Berlin & Heidelberg, DE |publisher=Springer Berlin Heidelberg | doi = 10.1007/978-3-642-79634-0_16 |isbn=978-3-642-79636-4 }}</ref> These texts, and other widely circulated publications in the 1990s, helped to establish the popular image of mass extinctions as a "big five" alongside many smaller extinctions through prehistory.

=== New data on genera: Sepkoski's compendium ===
[[File:Bambach 2006 extinction graphs.png|thumb|350x350px|Major [[Phanerozoic]] extinctions tracked via proportional genera extinctions by Bambach (2006)]]
Though Sepkoski died in 1999, his marine genera compendium was formally published in 2002. This prompted a new wave of studies into the dynamics of mass extinctions.<ref name="Sepkoski_2002">{{Cite journal | vauthors = Sepkoski Jr JJ |date=2002 | veditors = Jablonski D, Foote M |title=A Compendium of Fossil Marine Animal Genera |url=https://www.biodiversitylibrary.org/item/40634#page/5/mode/1up |journal=Bulletins of American Paleontology |volume=363 |pages=1–560}}</ref> These papers utilized the compendium to track origination rates (the rate that new species appear or [[Speciation|speciate]]) parallel to extinction rates in the context of geological stages or substages.<ref name="Foote_2000">{{Cite journal | vauthors = Foote M |date=2000 |title=Origination and extinction components of taxonomic diversity: General problems |url= https://www.cambridge.org/core/journals/paleobiology/article/abs/origination-and-extinction-components-of-taxonomic-diversity-general-problems/7FE12B43106FC20C9AFC4031F72A56F9 |journal=Paleobiology |language=en |volume=26 |issue=S4 |pages=74–102 |doi=10.1017/S0094837300026890 |bibcode=2000Pbio...26S..74F |s2cid=53341052 |issn=0094-8373|url-access=subscription }}</ref> A review and re-analysis of Sepkoski's data by Bambach (2006) identified 18 distinct mass extinction intervals, including 4 large extinctions in the [[Cambrian]]. These fit Sepkoski's definition of extinction, as short substages with large diversity loss and overall high extinction rates relative to their surroundings.<ref name="Bambach_2006">{{Cite journal | vauthors = Bambach RK |date= May 2006 |title=Phanerozoic Biodiversity Mass Extinctions |journal=Annual Review of Earth and Planetary Sciences |language=en |volume=34 |issue=1 |pages=127–155 |doi=10.1146/annurev.earth.33.092203.122654 |bibcode= 2006AREPS..34..127B |issn=0084-6597}}</ref>

Bambach et al. (2004) considered each of the "Big Five" extinction intervals to have a different pattern in the relationship between origination and extinction trends. Moreover, background extinction rates were broadly variable and could be separated into more severe and less severe time intervals. Background extinctions were least severe relative to the origination rate in the middle Ordovician-early Silurian, late Carboniferous-Permian, and Jurassic-recent. This argues that the Late Ordovician, end-Permian, and end-Cretaceous extinctions were statistically significant outliers in biodiversity trends, while the Late Devonian and end-Triassic extinctions occurred in time periods that were already stressed by relatively high extinction and low origination.<ref>{{Cite journal | vauthors = Bambach RK, Knoll AH, Wang SC |date=2004 |title=Origination, extinction, and mass depletions of marine diversity |url=https://www.cambridge.org/core/journals/paleobiology/article/abs/origination-extinction-and-mass-depletions-of-marine-diversity/15BF4851C6E3C95D8486926A87ECD9B3B3 |journal=Paleobiology |language=en |volume=30 |issue=4 |pages=522–542 |doi=10.1666/0094-8373(2004)030<0522:OEAMDO>2.0.CO;2 |bibcode=2004Pbio...30..522B |s2cid=17279135 |issn=0094-8373}}</ref>

Computer models run by Foote (2005) determined that abrupt pulses of extinction fit the pattern of prehistoric biodiversity much better than a gradual and continuous background extinction rate with smooth peaks and troughs. This strongly supports the utility of rapid, frequent mass extinctions as a major driver of diversity changes. Pulsed origination events are also supported, though to a lesser degree that is largely dependent on pulsed extinctions.<ref>{{Cite journal | vauthors = Foote M |date=2005 |title=Pulsed origination and extinction in the marine realm |journal=Paleobiology |volume=31 |issue=1 |pages=6–20 |doi=10.1666/0094-8373(2005)031<0006:POAEIT>2.0.CO;2|bibcode=2005Pbio...31....6F |s2cid=53469954 |url=http://doc.rero.ch/record/14957/files/PAL_E2104.pdf }}</ref>

Similarly, Stanley (2007) used extinction and origination data to investigate turnover rates and extinction responses among different evolutionary faunas and taxonomic groups. In contrast to previous authors, his diversity simulations show support for an overall exponential rate of biodiversity growth through the entire Phanerozoic.<ref>{{Cite journal | vauthors = Stanley SM |date=2007 |title=Memoir 4: An Analysis of the History of Marine Animal Diversity |journal=Paleobiology |language=en |volume=33 |issue=S4 |pages=1–55 |doi=10.1017/S0094837300019217 |bibcode=2007Pbio...33Q...1S |s2cid=90130435 |issn=0094-8373}}</ref>

=== Tackling biases in the fossil record ===
[[File:Signor Lipps.gif|thumb|252x252px|An illustration of the [[Signor–Lipps effect|Signor-Lipps effect]], a geological bias that posits that increased fossil sampling would help to better constrain the exact time when an organism truly goes extinct.]]
As data continued to accumulate, some authors began to re-evaluate Sepkoski's sample using methods meant to account for [[sampling bias]]es. As early as 1982, a paper by Phillip W. Signor and [[Jere H. Lipps]] noted that the true sharpness of extinctions was diluted by the incompleteness of the fossil record.<ref>Signor III, P. W. and Lipps, J. H. (1982) "[http://specialpapers.gsapubs.org/content/190/291.full.pdf Sampling bias, gradual extinction patterns, and catastrophes in the fossil record]", in ''Geological implications of impacts of large asteroids and comets on the Earth'' (ed. L. T. Silver and P. H. Schultz), Geological Society of America Special Publication, vol. 190, pp. 291–296.</ref> This phenomenon, later called the [[Signor–Lipps effect|Signor-Lipps effect]], notes that a species' true extinction must occur after its last fossil, and that origination must occur before its first fossil. Thus, species that appear to die out just prior to an abrupt extinction event may instead be a victim of the event, despite an apparent gradual decline looking at the fossil record alone. A model by Foote (2007) found that many geological stages had artificially inflated extinction rates due to Signor-Lipps "backsmearing" from later stages with extinction events.<ref name="Foote_2007">{{Cite journal | vauthors = Foote M |date=2007 |title=Extinction and quiescence in marine animal genera |url=https://www.cambridge.org/core/product/identifier/S0094837300023794/type/journal_article |journal=Paleobiology |language=en |volume=33 |issue=2 |pages=261–272 |doi=10.1666/06068.1 |s2cid=53402257 |issn=0094-8373|url-access=subscription }}</ref>
[[File:Foote 2007 Kocsis 2019 extinction graphs.png|left|thumb|502x502px|Estimated extinction rates among genera through time. From Foote (2007), top, and Kocsis et al. (2019), bottom]]
Other biases include the difficulty in assessing taxa with high turnover rates or restricted occurrences, which cannot be directly assessed due to a lack of fine-scale temporal resolution. Many paleontologists opt to assess diversity trends by randomized sampling and [[Rarefaction (ecology)|rarefaction]] of fossil abundances rather than raw temporal range data, in order to account for all of these biases. But that solution is influenced by biases related to sample size. One major bias in particular is the "[[Pull of the recent]]", the fact that the fossil record (and thus known diversity) generally improves closer to the modern day. This means that biodiversity and abundance for older geological periods may be underestimated from raw data alone.<ref name="Foote_2000" /><ref name="Foote_2007" /><ref name="Alroy_2008" />

[[John Alroy|Alroy]] (2010) attempted to circumvent sample size-related biases in diversity estimates using a method he called "[[shareholder]] quorum subsampling" (SQS). In this method, fossils are sampled from a "collection" (such as a time interval) to assess the relative diversity of that collection. Every time a new species (or other [[taxon]]) enters the sample, it brings over all other fossils belonging to that species in the collection (its "[[Share (finance)|share]]" of the collection). For example, a skewed collection with half its fossils from one species will immediately reach a sample share of 50% if that species is the first to be sampled. This continues, adding up the sample shares until a "coverage" or "[[quorum]]" is reached, referring to a pre-set desired sum of share percentages. At that point, the number of species in the sample are counted. A collection with more species is expected to reach a sample quorum with more species, thus accurately comparing the relative diversity change between two collections without relying on the biases inherent to sample size.<ref name="Alroy_2010">{{Cite journal | vauthors = Alroy J |date=2010 |title=Fair Sampling of Taxonomic Richness and Unbiased Estimation of Origination and Extinction Rates |url=http://dx.doi.org/10.1017/s1089332600001819 |journal=The Paleontological Society Papers |volume=16 |pages=55–80 |doi=10.1017/s1089332600001819 |issn=1089-3326|url-access=subscription }}</ref>

Alroy also elaborated on three-timer algorithms, which are meant to counteract biases in estimates of extinction and origination rates. A given taxon is a "three-timer" if it can be found before, after, and within a given time interval, and a "two-timer" if it overlaps with a time interval on one side. Counting "three-timers" and "two-timers" on either end of a time interval, and sampling time intervals in sequence, can together be combined into equations to predict extinction and origination with less bias.<ref name="Alroy_2010" /> In subsequent papers, Alroy continued to refine his equations to improve lingering issues with precision and unusual samples.<ref>{{Cite journal | vauthors = Alroy J |date=2014 |title=Accurate and precise estimates of origination and extinction rates |url=https://www.cambridge.org/core/product/identifier/S0094837300001871/type/journal_article |journal=Paleobiology |language=en |volume=40 |issue=3 |pages=374–397 |doi=10.1666/13036 |s2cid=53125415 |issn=0094-8373|url-access=subscription }}</ref><ref>{{Cite journal | vauthors = Alroy J |date=2015 |title=A more precise speciation and extinction rate estimator |url=https://www.cambridge.org/core/product/identifier/S0094837315000263/type/journal_article |journal=Paleobiology |language=en |volume=41 |issue=4 |pages=633–639 |doi=10.1017/pab.2015.26 |bibcode=2015Pbio...41..633A |s2cid=85842940 |issn=0094-8373|url-access=subscription }}</ref>

McGhee et al. (2013), a paper thatprimarily focused on ecological effects of mass extinctions, also published new estimates of extinction severity based on Alroy's methods. Many extinctions were significantly more impactful under these new estimates, though some were less prominent.<ref name="McGhee_2013">{{Cite journal | vauthors = McGhee Jr GR, Clapham ME, Sheehan PM, Bottjer DJ, Droser ML |date= January 2013 |title=A new ecological-severity ranking of major Phanerozoic biodiversity crises |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=370 |pages=260–270 |doi=10.1016/j.palaeo.2012.12.019 |bibcode= 2013PPP...370..260M |issn=0031-0182}}</ref>

Stanley (2016) was another paper that attempted to remove two common errors in previous estimates of extinction severity. The first error was the unjustified removal of "singletons", genera unique to only a single time slice. Their removal would mask the influence of groups with high turnover rates or lineages cut short early in their diversification. The second error was the difficulty in distinguishing background extinctions from brief mass extinction events within the same short time interval. To circumvent this issue, background rates of diversity change (extinction/origination) were estimated for stages or substages without mass extinctions, and then assumed to apply to subsequent stages with mass extinctions. For example, the [[Santonian]] and [[Campanian]] stages were each used to estimate diversity changes in the [[Maastrichtian]] prior to the K-Pg mass extinction. Subtracting background extinctions from extinction tallies had the effect of reducing the estimated severity of the six sampled mass extinction events. This effect was stronger for mass extinctions that occurred in periods with high rates of background extinction, like the Devonian.<ref name="Stanley_2016">{{Cite journal | vauthors = Stanley SM |date= October 2016 |title=Estimates of the magnitudes of major marine mass extinctions in earth history |journal= Proceedings of the National Academy of Sciences|language=en |volume=113 |issue=42 |pages= E6325–E6334 |doi=10.1073/pnas.1613094113 |issn=0027-8424 |pmc=5081622 |pmid=27698119|bibcode= 2016PNAS..113E6325S |doi-access= free }}</ref>

==Uncertainty in the Proterozoic and earlier eons==
Because most diversity and [[biomass (ecology)|biomass]] on Earth is [[microbial]], and thus difficult to measure via fossils, extinction events placed on-record are those that affect the easily observed, biologically complex component of the [[biosphere]] rather than the total diversity and abundance of life.<ref>{{cite journal |vauthors=Nee S |date=August 2004 |title=Extinction, slime, and bottoms |journal=PLOS Biology |volume=2 |issue=8 |pages=E272 |doi= 10.1371/journal.pbio.0020272 |pmc=509315 |pmid=15314670 |doi-access=free }}</ref> For this reason, well-documented extinction events are confined to the [[Phanerozoic eon]] – with the sole exception of the [[Great Oxidation Event|Oxygen Catastrophe]] in the [[Proterozoic]] – since before the Phanerozoic, all living organisms were either microbial, or if multicellular then soft-bodied. Perhaps due to the absence of a robust microbial fossil record, mass extinctions might only ''seem'' to be mainly a Phanerozoic phenomenon, with merely the ''observable'' extinction rates appearing low before large complex organisms with hard body parts arose.<ref name=Butterfield2007>{{cite journal |vauthors=Butterfield NJ |year=2007 |title=Macroevolution and macroecology through deep time |journal= Palaeontology |volume=50 |issue=1 |pages=41–55 |doi=10.1111/j.1475-4983.2006.00613.x |bibcode=2007Palgy..50...41B |s2cid=59436643 |url= http://eprints.esc.cam.ac.uk/174/1/Butterfield__Palaeontolgy_50_Pt_1_2007_.pdf |access-date=6 October 2019 |url-status=dead |archive-url= https://web.archive.org/web/20220721114458/http://eprints.esc.cam.ac.uk/174/1/Butterfield__Palaeontolgy_50_Pt_1_2007_.pdf |archive-date=21 July 2022 }}</ref>

Extinction occurs at an uneven rate. Based on the [[fossil record]], the [[background extinction rate|background rate of extinctions]] on Earth is about two to five [[taxonomy (biology)|taxonomic]] [[family (biology)|families]] of [[marine animal]]s every million years.{{efn|
Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to [[land animal]]s.
}}

The Oxygen Catastrophe, which occurred around 2.45&nbsp;billion years ago in the [[Paleoproterozoic]], is plausible as the first-ever major extinction event. It was perhaps also the worst-ever, in some sense, but with the Earth's ecology just before that time so poorly understood, and the concept of [[prokaryote]] genera so different from genera of complex life, that it would be difficult to meaningfully compare it to any of the "Big Five" even if Paleoproterozoic life were better known.<ref>{{cite news |vauthors=Plait P |date=28 July 2014 |title=Poisoned planet |website= Slate.com |url= https://slate.com/technology/2014/07/the-great-oxygenation-event-the-earths-first-mass-extinction.html |access-date=8 July 2019}}</ref>

Since the [[Cambrian explosion]], five further major mass extinctions have significantly exceeded the background extinction rate. The most recent and best-known, the [[Cretaceous–Paleogene extinction event]], which occurred approximately {{period start|Paleogene}}&nbsp;Ma (million years ago), was a large-scale mass extinction of animal and plant species in a geologically short period of time.<ref name="Ward 2006">{{cite magazine |vauthors=Ward PD |date=October 2006 |title=Impact from the deep |magazine=[[Scientific American]] |volume=295 |issue=4 |pages=64–71 |bibcode=2006SciAm.295d..64W |doi=10.1038/scientificamerican1006-64 |doi-broken-date=1 November 2024 |pmid=16989482}}</ref> In addition to the five major Phanerozoic mass extinctions, there are numerous lesser ones, and the ongoing mass extinction caused by human activity is sometimes called the [[Holocene extinction|sixth mass extinction]].<ref>{{cite magazine |vauthors=Kluger J |date=25 July 2014 |title=The sixth great extinction is underway – and we're to blame |magazine=[[Time (magazine)|Time]] |url=https://time.com/3035872/sixth-great-extinction/ |access-date=December 14, 2016 }}
:
{{cite news |date=June 22, 2015 |title=Earth is on brink of a sixth mass extinction, scientists say, and it's humans' fault |newspaper=[[The Washington Post]] |url=https://www.washingtonpost.com/news/morning-mix/wp/2015/06/22/the-earth-is-on-the-brink-of-a-sixth-mass-extinction-scientists-say-and-its-humans-fault/ |access-date=December 14, 2016 |vauthors=Kaplan S}}
:
{{cite news |date=October 20, 2015 |title=How humans are driving the sixth mass extinction |newspaper=[[The Guardian]] |url=https://www.theguardian.com/environment/radical-conservation/2015/oct/20/the-four-horsemen-of-the-sixth-mass-extinction |access-date=December 14, 2016 |vauthors=Hance J}}
:
{{cite news |title=Vanishing: The Earth's 6th mass extinction |website=[[CNN]] |url=http://www.cnn.com/specials/world/vanishing-earths-mass-extinction |access-date=December 19, 2016}}
:
{{cite journal |vauthors=Mason R |date=2015 |title=The sixth mass extinction and chemicals in the environment: our environmental deficit is now beyond nature's ability to regenerate |journal=J. Biol. Phys. Chem. |volume=15 |issue=3 |pages=160–176 |doi=10.4024/10MA15F.jbpc.15.03}}
:
{{cite news |date=January 17, 2022 |title=Study confirms sixth mass extinction is currently underway, caused by humans |newspaper=[[The Independent]] |location= |url=https://www.independent.co.uk/climate-change/news/sixth-mass-extinction-global-biodiversity-b1994346.html |access-date=January 18, 2022 |vauthors=Sankaran V}}</ref>

==Evolutionary importance==
{{Life timeline}}
{{See also|Evolutionary radiation|Macroevolution}}

Mass extinctions have sometimes accelerated the [[evolution]] of [[life|life on Earth]]. When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the newly dominant group is "superior" to the old but usually because an extinction event eliminates the old, dominant group and makes way for the new one, a process known as [[adaptive radiation]].<ref>
{{cite book | vauthors = Benton MJ | author-link = Michael Benton | title = Vertebrate Palaeontology | publisher = Blackwell | year = 2004 | chapter = 6. Reptiles Of the Triassic | chapter-url = http://www.blackwellpublishing.com/book.asp?ref=0632056371 | isbn = 978-0-04-566002-5 }}</ref><ref>{{cite journal | vauthors = van Valkenburgh B | year = 1999 | title = Major patterns in the history of carnivorous mammals | journal = Annual Review of Earth and Planetary Sciences | volume = 27 | pages = 463–93 | doi = 10.1146/annurev.earth.27.1.463 | bibcode = 1999AREPS..27..463V | url = https://zenodo.org/record/890156 }}</ref>

For example, [[mammaliaformes]] ("almost mammals") and then [[mammal]]s existed throughout the reign of the [[dinosaur]]s, but could not compete in the large terrestrial vertebrate niches that dinosaurs monopolized. The [[Cretaceous–Paleogene extinction event|end-Cretaceous]] mass extinction removed the non-avian dinosaurs and made it possible for mammals to expand into the large terrestrial vertebrate niches. The dinosaurs themselves had been beneficiaries of a previous mass extinction, the [[Triassic–Jurassic extinction event|end-Triassic]], which eliminated most of their chief rivals, the [[crurotarsans]]. Similarly, within [[Synapsida]], the replacement of taxa that originated in the earliest, [[Pennsylvanian (geology)|Pennsylvanian]] and [[Cisuralian]] evolutionary radiation (often still called "[[pelycosaur]]s", though this is a [[paraphyletic]] group) by [[Therapsida|therapsids]] occurred  around the [[Kungurian]]/[[Roadian]] transition, which is often called [[Olson's Extinction|Olson's extinction]]<ref name="Brocklehurst 2018">{{cite journal |last1=Brocklehurst |first1=Neil |title=An examination of the impact of Olson's extinction on tetrapods from Texas |journal=PeerJ |date=15 May 2018 |volume=6 |pages=e4767 |doi=10.7717/peerj.4767|doi-access=free |pmid=29780669 |pmc=5958880 }}</ref><ref name="Brocklehurst 2020">{{cite journal |last1=Brocklehurst |first1=Neil |title=Olson's Gap or Olson's Extinction? A Bayesian tip-dating approach to resolving stratigraphic uncertainty |journal=Proceedings of the Royal Society B: Biological Sciences |date=10 June 2020 |volume=287 |issue=1928 |pages=20200154 |doi=10.1098/rspb.2020.0154 |pmid=32517621 |url=https://doi.org/10.1098/rspb.2020.0154 |language=en |issn=0962-8452|pmc=7341920 }}</ref> (which may be a slow decline over 20 Ma<ref name="Didier & Laurin 2024">{{cite journal |last1=Didier |first1=Gilles |last2=Laurin |first2=Michel |title=Testing extinction events and temporal shifts in diversification and fossilization rates through the skyline Fossilized Birth-Death (FBD) model: The example of some mid-Permian synapsid extinctions |journal=Cladistics |date=June 2024 |volume=40 |issue=3 |pages=282–306 |doi=10.1111/cla.12577 |pmid=38651531 |language=en |issn=0748-3007|doi-access=free }}</ref> rather than a dramatic, brief event).

Another point of view put forward in the [[Escalation hypothesis]] predicts that species in ecological niches with more organism-to-organism conflict will be less likely to survive extinctions. This is because the very traits that keep a species numerous and viable under fairly static conditions become a burden once population levels fall among competing organisms during the dynamics of an extinction event.

Furthermore, many groups that survive mass extinctions do not recover in numbers or diversity, and many of these go into long-term decline, and these are often referred to as "[[Dead Clade Walking|Dead Clades Walking]]".<ref>
{{cite journal | vauthors = Jablonski D | title = Survival without recovery after mass extinctions | journal =   Proceedings of the National Academy of Sciences| volume = 99 | issue = 12 | pages = 8139–8144 | date = June 2002 | pmid = 12060760 | pmc = 123034 | doi = 10.1073/pnas.102163299 | bibcode = 2002PNAS...99.8139J | doi-access = free }}
</ref>
However, clades that survive for a considerable period of time after a mass extinction, and that were reduced to only a few species, are likely to have experienced a rebound effect called the "[[push of the past]]".<ref name="POTPa">
{{cite journal | vauthors = Budd GE, Mann RP | title = History is written by the victors: The effect of the push of the past on the fossil record | journal = Evolution; International Journal of Organic Evolution | volume = 72 | issue = 11 | pages = 2276–2291 | date = November 2018 | pmid = 30257040 | pmc = 6282550 | doi = 10.1111/evo.13593 }}
</ref>

Darwin was firmly of the opinion that biotic interactions, such as competition for food and space – the 'struggle for existence' – were of considerably greater importance in promoting evolution and extinction than changes in the physical environment. He expressed this in ''[[The Origin of Species]]'':
: "Species are produced and exterminated by slowly acting causes ... and the most import of all causes of organic change is one which is almost independent of altered ... physical conditions, namely the mutual relation of organism to organism – the improvement of one organism entailing the improvement or extermination of others".<ref>{{cite book | vauthors = Hallam A, Wignall PB | author1-link = Hallam, Anthony | year = 2002 | title = Mass Extinctions and their Aftermath | place = New York, NY | publisher = Oxford University Press }}</ref>

==Patterns in frequency==
Various authors have suggested that extinction events occurred periodically, every 26 to 30&nbsp;million years,<ref>{{cite magazine | vauthors = Beardsley T  |year = 1988 |title = Star-struck? |magazine =[[Scientific American]] |volume = 258 |issue = 4 |pages = 37–40 |doi = 10.1038/scientificamerican0488-37b |bibcode = 1988SciAm.258d..37B}}</ref><ref name=Raup1984>{{cite journal | vauthors = Raup DM, Sepkoski JJ | title = Periodicity of extinctions in the geologic past | journal =  Proceedings of the National Academy of Sciences| volume = 81 | issue = 3 | pages = 801–805 | date = February 1984 | pmid = 6583680 | pmc = 344925 | doi = 10.1073/pnas.81.3.801 | bibcode = 1984PNAS...81..801R | doi-access = free }}</ref> or that diversity fluctuates episodically about every 62 million years.<ref name=Rohde2005>
Different cycle lengths have been proposed; e.g. by {{cite journal | vauthors = Rohde RA, Muller RA | title = Cycles in fossil diversity | journal = Nature | volume = 434 | issue = 7030 | pages = 208–210 | date = March 2005 | pmid = 15758998 | doi = 10.1038/nature03339 | s2cid = 32520208 | bibcode = 2005Natur.434..208R }}</ref> Various ideas, mostly regarding [[Astronomy|astronomical]] influences, attempt to explain the supposed pattern, including the presence of a [[Nemesis (hypothetical star)|hypothetical companion star]] to the Sun,<ref>{{cite web | vauthors = Muller RA |title = Nemesis |website = Muller.lbl.gov |publisher = [[Lawrence Berkeley Laboratory]] |url = http://muller.lbl.gov/pages/lbl-nem.htm |access-date = 2007-05-19}}</ref><ref>
{{cite journal | vauthors = Melott AL, Bambach RK | date = July 2010 | title = Nemesis reconsidered | journal = [[Monthly Notices of the Royal Astronomical Society]] | volume = 407 | issue = 1 | pages = L99–L102 | doi = 10.1111/j.1745-3933.2010.00913.x | doi-access = free | arxiv = 1007.0437 | bibcode = 2010MNRAS.407L..99M | s2cid = 7911150 | url = http://www.centauri-dreams.org/?p=13357 | access-date = 2010-07-02 }}</ref> oscillations in the galactic plane, or passage through the Milky Way's spiral arms.<ref name="Gillmana2008">
{{cite journal | vauthors = Gillman M, Erenler H | year = 2008 | title = The galactic cycle of extinction | journal = International Journal of Astrobiology | volume = 7 | issue = 1 | pages = 17–26 | doi = 10.1017/S1473550408004047 | bibcode = 2008IJAsB...7...17G | issn = 1475-3006 | citeseerx = 10.1.1.384.9224 | s2cid = 31391193 | url = http://oro.open.ac.uk/11603/1/S1473550408004047a.pdf | access-date = 2018-04-02 }}
</ref> However, other authors have concluded that the data on marine mass extinctions do not fit with the idea that mass extinctions are periodic, or that ecosystems gradually build up to a point at which a mass extinction is inevitable.<ref name=Alroy_2008>{{cite journal | vauthors = Alroy J | title = Colloquium paper: dynamics of origination and extinction in the marine fossil record | journal =  Proceedings of the National Academy of Sciences of the United States of America| volume = 105 | issue = Supplement 1 | pages = 11536–11542 | date = August 2008 | pmid = 18695240 | pmc = 2556405 | doi = 10.1073/pnas.0802597105 | doi-access = free | bibcode = 2008PNAS..10511536A }}</ref> Many of the proposed correlations have been argued to be spurious or lacking statistical significance.<ref>{{cite journal | vauthors = Bailer-Jones CA | date = July 2009 | title = The evidence for and against astronomical impacts on climate change and mass extinctions: A review | journal = International Journal of Astrobiology | volume = 8 | issue = 3 | pages = 213–219 | doi = 10.1017/S147355040999005X |bibcode = 2009IJAsB...8..213B |arxiv = 0905.3919 | s2cid = 2028999|issn=1475-3006}}</ref><ref>{{cite journal | vauthors = Overholt AC, Melott AL, Pohl M | year = 2009 | title = Testing the link between terrestrial climate change and galactic spiral arm transit | journal = The Astrophysical Journal | volume = 705 | issue = 2 | pages = L101–03 | doi = 10.1088/0004-637X/705/2/L101 | bibcode=2009ApJ...705L.101O |arxiv = 0906.2777 | s2cid = 734824}}</ref><ref>{{Cite journal | vauthors = Erlykin AD, Harper DA, Sloan T, Wolfendale AW |date=2017 | veditors = Smith A |title=Mass extinctions over the last 500 myr: an astronomical cause? |journal=Palaeontology |language=en |volume=60 |issue=2 |pages=159–167 |doi=10.1111/pala.12283|bibcode=2017Palgy..60..159E |s2cid=133407217 |doi-access=free }}</ref> Others have argued that there is strong evidence supporting periodicity in a variety of records,<ref name="Melott2011">{{cite journal | vauthors = Melott AL, Bambach RK | year = 2011 | title = A{{grey|[n]}} ubiquitous ~62&nbsp;Myr periodic fluctuation superimposed on general trends in fossil biodiversity. I. Documentation | journal = Paleobiology | volume = 37 | pages = 92–112 | doi = 10.1666/09054.1 | arxiv = 1005.4393 | s2cid = 1905891 }}</ref> and additional evidence in the form of coincident periodic variation in nonbiological geochemical variables such as Strontium isotopes,<ref name="Melott et al. 2012">{{cite journal | vauthors = Melott AL, Bambach RK, Petersen KD, McArthur JM | display-authors = etal | year = 2012 | title = A ~60 Myr periodicity is common to marine-87Sr/86Sr, fossil biodiversity, and large-scale sedimentation: what does the periodicity reflect? | journal = Journal of Geology | volume = 120 | issue = 2 | pages = 217–226 | arxiv = 1206.1804 | bibcode = 2012JG....120..217M | doi = 10.1086/663877 | s2cid = 18027758 }}</ref> flood basalts, anoxic events, orogenies, and evaporite deposition. One explanation for this proposed cycle is carbon storage and release by oceanic crust, which exchanges carbon between the atmosphere and mantle.<ref>{{cite journal | vauthors = Müller RD, Dutkiewicz A | title = Oceanic crustal carbon cycle drives 26-million-year atmospheric carbon dioxide periodicities | journal = Science Advances | volume = 4 | issue = 2 | pages = eaaq0500 | date = February 2018 | pmid = 29457135 | pmc = 5812735 | doi = 10.1126/sciadv.aaq0500 | bibcode = 2018SciA....4..500M }}</ref>
{{Phanerozoic biodiversity}}
Mass extinctions are thought to result when a long-term stress is compounded by a short-term shock.<ref name=Arens2008>{{cite journal | vauthors = Arens NC, West ID | year = 2008 | title = Press-pulse: a general theory of mass extinction? | journal = Paleobiology| volume = 34 | issue = 4 | pages = 456–471 | doi = 10.1666/07034.1 | bibcode = 2008Pbio...34..456A | s2cid = 56118514| url = http://doc.rero.ch/record/16048/files/PAL_E3838.pdf }}</ref> Over the course of the [[Phanerozoic]], individual taxa appear to have become less likely to suffer extinction,<ref name=Wang2008>{{cite journal | vauthors = Wang SC, Bush AM | year = 2008 | title = Adjusting global extinction rates to account for taxonomic susceptibility | journal = Paleobiology | volume = 34 | issue = 4 | pages = 434–55 | doi = 10.1666/07060.1 | s2cid = 16260671 | url = http://www.swarthmore.edu/NatSci/swang1/Publications/}}</ref> which may reflect more robust food webs, as well as fewer extinction-prone species, and other factors such as continental distribution.<ref name=Wang2008/> However, even after accounting for sampling bias, there does appear to be a gradual decrease in extinction and origination rates during the Phanerozoic.<ref name=Alroy_2008/> This may represent the fact that groups with higher turnover rates are more likely to become extinct by chance; or it may be an artefact of taxonomy: families tend to become more speciose, therefore less prone to extinction, over time;<ref name=Alroy_2008/> and larger taxonomic groups (by definition) appear earlier in geological time.<ref name="Budd2003">{{cite journal | vauthors = Budd GE | title = The Cambrian fossil record and the origin of the phyla | journal = Integrative and Comparative Biology | volume = 43 | issue = 1 | pages = 157–165 | date = February 2003 | pmid = 21680420 | doi = 10.1093/icb/43.1.157 | doi-access = free }}</ref>

It has also been suggested that the oceans have gradually become more hospitable to life over the last 500 million years, and thus less vulnerable to mass extinctions,{{efn|
[[Dissolved oxygen]] became more widespread and penetrated to greater depths; the development of life on land reduced the run-off of nutrients and hence the risk of [[eutrophication]] and [[anoxic event]]s; and marine ecosystems became more diversified so that [[food chain]]s were less likely to be disrupted.
}}<ref>{{cite journal | vauthors = Martin RE | year = 1995 | title = Cyclic and secular variation in microfossil biomineralization: Clues to the biogeochemical evolution of Phanerozoic oceans | journal = Global and Planetary Change | volume = 11 | issue = 1 | pages = 1–23 | doi = 10.1016/0921-8181(94)00011-2 | bibcode = 1995GPC....11....1M }}</ref><ref>{{cite journal | vauthors = Martin RE | year = 1996 | title = Secular increase in nutrient levels through the Phanerozoic: Implications for productivity, biomass, and diversity of the marine biosphere | journal = PALAIOS | volume = 11 | issue = 3 | pages = 209–219 | doi = 10.2307/3515230 | jstor = 3515230 | bibcode = 1996Palai..11..209M }}
</ref>
but susceptibility to extinction at a taxonomic level does not appear to make mass extinctions more or less probable.<ref name=Wang2008/>

==Causes==
There is still debate about the causes of all mass extinctions. In general, large extinctions may result when a biosphere under long-term stress undergoes a short-term shock.<ref name="Arens2008"/> An underlying mechanism appears to be present in the correlation of extinction and origination rates to diversity. High diversity leads to a persistent increase in extinction rate; low diversity to a persistent increase in origination rate. These presumably ecologically controlled relationships likely amplify smaller perturbations (asteroid impacts, etc.) to produce the global effects observed.<ref name=Alroy_2008/>

===Identifying causes of specific mass extinctions===
A good theory for a particular mass extinction should: 
* explain all of the losses, not just focus on a few groups (such as dinosaurs); 
* explain why particular groups of organisms died out and why others survived;
* provide mechanisms that are strong enough to cause a mass extinction but not a total extinction; 
* be based on events or processes that can be shown to have happened, not just inferred from the extinction.

It may be necessary to consider combinations of causes. For example, the marine aspect of the [[Cretaceous–Paleogene extinction event|end-Cretaceous]] extinction appears to have been caused by several processes that partially overlapped in time and may have had different levels of significance in different parts of the world.<ref>{{cite journal | vauthors = Marshall CR, Ward PD | title = Sudden and Gradual Molluscan Extinctions in the Latest Cretaceous of Western European Tethys | journal = Science | volume = 274 | issue = 5291 | pages = 1360–1363 | date = November 1996 | pmid = 8910273 | doi = 10.1126/science.274.5291.1360 | s2cid = 1837900 | bibcode = 1996Sci...274.1360M }}</ref>

Arens and West (2006) proposed a "press / pulse" model in which mass extinctions generally require two types of cause: long-term pressure on the eco-system ("press") and a sudden catastrophe ("pulse") towards the end of the period of pressure.<ref>{{cite conference | vauthors = Arens NC, West ID |year=2006 |title=Press/pulse: A general theory of mass extinction? |conference=[[Geological Society of America]]
 |url=http://gsa.confex.com/gsa/2006AM/finalprogram/abstract_111772.htm  
 |archive-url=https://web.archive.org/web/20170118164705/https://gsa.confex.com/gsa/2006AM/finalprogram/abstract_111772.htm
 |archive-date=2017-01-18
}}
</ref>
Their statistical analysis of marine extinction rates throughout the [[Phanerozoic]] suggested that neither long-term pressure alone nor a catastrophe alone was sufficient to cause a significant increase in the extinction rate.

===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. 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|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/>

==Effects and recovery==
The effects of mass extinction events varied widely. After a major extinction event, usually only [[weed#Weeds as adaptable species|weedy species]] survive due to their ability to live in diverse habitats.<ref name=Quammen>{{cite magazine |title=Planet of Weeds | vauthors = Quammen D |magazine=Harper's Magazine |date=October 1998 |url= http://sep.csumb.edu/class/ESSP645/readings/Quammen%201998.pdf |access-date=November 15, 2012 }}</ref> Later, species diversify and occupy empty niches. Generally, it takes millions of years for [[biodiversity]] to recover after extinction events.<ref>{{cite news |title=Evolution imposes 'speed limit' on recovery after mass extinctions |website=ScienceDaily |date=April 8, 2019 |language=en |url=https://www.sciencedaily.com/releases/2019/04/190408114252.htm |access-date=2019-09-07}}</ref> In the most severe mass extinctions it may take 15 to 30 million years.<ref name="Quammen" />

The worst [[Phanerozoic]] event, the [[Permian–Triassic extinction event|Permian–Triassic extinction]], devastated life on Earth, killing over 90% of species. Life seemed to recover quickly after the P-T extinction, but this was mostly in the form of [[pioneer organism|disaster taxa]], such as the hardy ''[[Lystrosaurus]]''. The most recent research indicates that the specialized animals that formed complex ecosystems, with high biodiversity, complex food webs and a variety of niches, took much longer to recover. It is thought that this long recovery was due to successive waves of extinction that inhibited recovery, as well as prolonged environmental stress that continued into the Early Triassic. Recent research indicates that recovery did not begin until the start of the mid-Triassic, four to six million years after the extinction;<ref name="LehrmannRamezanBowring2006TimingOfRecovery">
{{cite journal | vauthors = Lehrmann DJ, Ramezani J, Bowring SA, Martin MW, Montgomery P, Enos P, Payne JL, Orchard MJ, Hongmei W, Jiayong W | display-authors = 6 | date = December 2006 | title = Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China | journal = Geology | volume = 34 | issue = 12 | pages = 1053–1056 | doi = 10.1130/G22827A.1 | bibcode = 2006Geo....34.1053L }}
</ref>
and some writers estimate that the recovery was not complete until 30 million years after the P-T extinction, that is, in the late Triassic.<ref name="SahneyBenton2008RecoveryFromProfoundExtinction">
{{cite journal | vauthors = Sahney S, Benton MJ | title = Recovery from the most profound mass extinction of all time | journal = Proceedings. Biological Sciences | volume = 275 | issue = 1636 | pages = 759–765 | date = April 2008 | pmid = 18198148 | pmc = 2596898 | doi = 10.1098/rspb.2007.1370 | author2-link = Michael Benton }}
</ref> Subsequent to the P-T extinction, there was an increase in provincialization, with species occupying smaller ranges – perhaps removing incumbents from niches and setting the stage for an eventual rediversification.<ref name="Sidor2013">{{cite journal | vauthors = Sidor CA, Vilhena DA, Angielczyk KD, Huttenlocker AK, Nesbitt SJ, Peecook BR, Steyer JS, Smith RM, Tsuji LA | display-authors = 6 | title = Provincialization of terrestrial faunas following the end-Permian mass extinction | journal = Proceedings of the National Academy of Sciences| volume = 110 | issue = 20 | pages = 8129–8133 | date = May 2013 | pmid = 23630295 | pmc = 3657826 | doi = 10.1073/pnas.1302323110 | bibcode = 2013PNAS..110.8129S | doi-access = free }}
</ref>

The effects of mass extinctions on plants are somewhat harder to quantify, given the biases inherent in the plant fossil record. Some mass extinctions (such as the end-Permian) were equally catastrophic for plants, whereas others, such as the end-Devonian, did not affect the flora.<ref name="Cascales-Miñana2011">{{cite journal | vauthors = Cascales-Miñana B, Cleal CJ | year = 2011 | title = Plant fossil record and survival analyses | journal = Lethaia | volume = 45 | pages = 71–82 | doi = 10.1111/j.1502-3931.2011.00262.x }}</ref>

==In media==
The term '''extinction level event (ELE)''' has been used in media.<ref>Lowry, B. (2016) ‘You, Me and the Apocalypse’, Variety, 330(16), pp. 84-.</ref><ref>Andrews, R.G. (2019) ‘If We Blow Up an Asteroid, It Might Put Itself Back Together: Trilobites’, New York Times (Online).</ref> The 1998 film [[Deep Impact (film)|Deep Impact]] describes a potential comet strike of earth as an E.L.E.<ref>[https://www.rogerebert.com/reviews/deep-impact-1998 Deep Impact]. ''Roger Ebert''. 8 May 1998. Retrieved 14 May 2024.</ref>

== See also ==
{{div col|colwidth=22em}}
* [[Bioevent]]
* [[Elvis taxon]]
* [[Endangered species]]
* [[Geologic time scale]]
* [[Global catastrophic risk]]
* [[Holocene extinction]]
* [[Human extinction]]
* [[Kačák Event]]
* [[Lazarus taxon]]
* [[List of impact structures on Earth]]
* [[List of largest volcanic eruptions]]
* [[List of possible impact structures on Earth]]
* [[Medea hypothesis]]
* [[Rare species]]
* [[Signor–Lipps effect]]
* [[Snowball Earth]]
* [[Speculative evolution]]
* [[The Sixth Extinction: An Unnatural History|''The Sixth Extinction: An Unnatural History'' (nonfiction book)]]
* [[Timeline of extinctions in the Holocene]]
* [[Late Pleistocene extinctions]]
{{div col end}}

==Footnotes==
{{notelist}}

== References ==
{{reflist|25em}}

== Further reading ==
{{refbegin}}
* {{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 | isbn = 978-0-06-236480-7 }}
{{refend}}
* Edmeades B (2021) Megafauna: First victims of the human-caused extinction | Houndstooth Press | isbn 978-1-5445-2651-5

== External links ==
* {{cite web
 |title=Calculate the effects of an impact
 |department=[[Lunar and Planetary Laboratory]]
 |place=Tucson, AZ
 |publisher=[[University of Arizona]]
 |url=http://www.lpl.arizona.edu/impacteffects/
}}
* {{cite web
 |title=Species Alliance
 |url=http://www.speciesalliance.com
}} – nonprofit organization producing a documentary about mass extinction titled ''"Call of Life: Facing the Mass Extinction"'' 
* {{cite web
 |title=Interstellar dust cloud-induced extinction theory
 |website=space.com
 |date=4 March 2005
 |url=http://www.space.com/scienceastronomy/050503_mass_extinctions.html
}}
* {{cite web
 |title=Sepkoski's Global Genus Database of Marine Animals
 |url=http://strata.geology.wisc.edu/jack
 |department=Geology
 |publisher=[[University of Wisconsin]]
}} – Calculate extinction rates for yourself!

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[[Category:History of climate variability and change]]
[[Category:Evolutionary biology]]
[[Category:Meteorological hypotheses]]
[[Category:Natural disasters]]