Editing Extinction event (section)

==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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|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>