Editing Permian–Triassic extinction event (section)

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

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

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

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

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

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

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

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