Editing Triassic–Jurassic extinction event (section)

=== Extraterrestrial impact ===
[[File:Manicouagan-EO.JPG|thumb|The [[Manicouagan Reservoir|Manicouagan reservoir]] in [[Quebec]], a massive crater formed by a Late Triassic impact. Radiometric dating has determined that it is about 13 million years older than the Triassic–Jurassic boundary, and thus an unlikely candidate for a mass extinction.]]
Some have hypothesized that an impact from an [[asteroid]] or [[comet]] caused the Triassic–Jurassic extinction,<ref name="GrahamRyderBook" /><ref name="Fowell19942" /> similar to the extraterrestrial object which was the main factor in the [[Cretaceous–Paleogene extinction event|Cretaceous–Paleogene extinction]] about 66 million years ago, as evidenced by the [[Chicxulub crater]] in Mexico. However, so far no impact crater of sufficient size has been dated to precisely coincide with the Triassic–Jurassic boundary.<ref name="TannerLucas" />

Nevertheless, the Late Triassic did experience several impacts, including the second-largest confirmed impact in the Mesozoic. The [[Manicouagan Reservoir]] in [[Quebec]] is one of the most visible large impact craters on Earth, and at {{cvt|100|km}} in diameter it is tied with the [[Eocene]] [[Popigai impact structure]] in [[Siberia]] as the [[List of impact craters on Earth|fourth-largest]] impact crater on Earth. Olsen ''et al.'' (1987) were the first scientists to link the Manicouagan crater to the Triassic–Jurassic extinction, citing its age which at the time was roughly considered to be Late Triassic.<ref name=":2" /> More precise [[radiometric dating]] by Hodych & Dunning (1992) has shown that the Manicouagan impact occurred about 214 million years ago, about 13 million years before the Triassic–Jurassic boundary. Therefore, it could not have been responsible for an extinction precisely at the Triassic–Jurassic boundary.<ref name=":0">{{Cite journal |last1=Hodych |first1=J. P. |last2=Dunning |first2=G. R. |date=1 January 1992 |title=Did the Manicouagan impact trigger end-of-Triassic mass extinction? |url=https://www.researchgate.net/publication/230892382 |journal=[[Geology (journal)|Geology]] |language=en |volume=20 |issue=1 |pages=51–54 |bibcode=1992Geo....20...51H |doi=10.1130/0091-7613(1992)020<0051:dtmite>2.3.co;2 |issn=0091-7613}}</ref> Nevertheless, the Manicouagan impact did have a widespread effect on the planet; a 214-million-year-old [[ejecta blanket]] of [[shocked quartz]] has been found in rock layers as far away as [[England]]<ref name=":1">{{Cite journal |last=Racki |first=Grzegorz |date=2010 |title=The Alvarez impact theory of mass extinction; limits to its applicability and the "great expectations syndrome" |url=https://www.app.pan.pl/archive/published/app57/app20110058.pdf |journal=[[Acta Palaeontologica Polonica]] |volume=57 |issue=4 |pages=681–702 |doi=10.4202/app.2011.0058 |s2cid=54021858 |doi-access=free}}</ref> and Japan. There is still a possibility that the Manicouagan impact was responsible for a small extinction midway through the Late Triassic at the Carnian–Norian boundary,<ref name=":0" /> although the disputed age of this boundary (and whether an extinction actually occurred in the first place) makes it difficult to correlate the impact with extinction.<ref name=":1" /> Onoue ''et al.'' (2016) alternatively proposed that the Manicouagan impact was responsible for a marine extinction in the middle of the Norian which affected radiolarians, sponges, conodonts, and Triassic ammonoids. Thus, the Manicouagan impact may have been partially responsible for the gradual decline in the latter two groups which culminated in their extinction at the Triassic–Jurassic boundary.<ref>{{Cite journal |last1=Onoue |first1=Tetsuji |last2=Sato |first2=Honami |last3=Yamashita |first3=Daisuke |last4=Ikehara |first4=Minoru |last5=Yasukawa |first5=Kazutaka |last6=Fujinaga |first6=Koichiro |last7=Kato |first7=Yasuhiro |last8=Matsuoka |first8=Atsushi |date=8 July 2016 |title=Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa |journal=[[Scientific Reports]] |volume=6 |pages=29609 |bibcode=2016NatSR...629609O |doi=10.1038/srep29609 |issn=2045-2322 |pmc=4937377 |pmid=27387863}}</ref> The boundary between the Adamanian and Revueltian land vertebrate faunal zones, which involved extinctions and faunal changes in tetrapods and plants, was possibly also caused by the Manicouagan impact, although discrepancies between magnetochronological and isotopic dating lead to some uncertainty.<ref>{{Cite journal |last1=Kent |first1=Dennis V. |last2=Olsen |first2=Paul E. |last3=Lepre |first3=Christopher |last4=Rasmussen |first4=Cornelia |last5=Mundil |first5=Roland |last6=Gehrels |first6=George E. |last7=Giesler |first7=Dominique |last8=Irmis |first8=Randall B. |last9=Geissman |first9=John W. |last10=Parker |first10=William G. |date=16 October 2019 |title=Magnetochronology of the entire Chinle Formation (Norian age) in a scientific drill core from Petrified Forest National Park (Arizona, USA) and implications for regional and global correlations in the Late Triassic |journal=[[Geochemistry, Geophysics, Geosystems]] |language=en |volume=20 |issue=11 |pages=4654–4664 |bibcode=2019GGG....20.4654K |doi=10.1029/2019GC008474 |issn=1525-2027 |s2cid=207980627 |hdl-access=free |hdl=10150/636323}}</ref>

Other Triassic craters are closer to the Triassic–Jurassic boundary but also much smaller than the Manicouagan reservoir. The eroded [[Rochechouart impact structure]] in [[France]] has most recently been dated to {{val|201|2}} million years ago,<ref name="Schmieder">{{cite journal |last=Schmieder |first=M. |author2=Buchner, E. |author3=Schwarz, W. H. |author4=Trieloff, M. |author5=Lambert, P. |date=2010-10-05 |title=A Rhaetian <sup>40</sup>Ar/<sup>39</sup>Ar age for the Rochechouart impact structure (France) and implications for the latest Triassic sedimentary record |journal=[[Meteoritics & Planetary Science]] |volume=45 |issue=8 |pages=1225–1242 |bibcode=2010M&PS...45.1225S |doi=10.1111/j.1945-5100.2010.01070.x |s2cid=129154084 |doi-access=free}}</ref> but at {{cvt|25|km}} across (possibly up to {{cvt|50|km|-1}} across originally), it appears to be too small to have affected the ecosystem,<ref name="RSmith">{{cite journal |last=Smith |first=Roff |date=2011-11-16 |title=Dark days of the Triassic: Lost world |journal=[[Nature (journal)|Nature]] |volume=479 |issue=7373 |pages=287–289 |bibcode=2011Natur.479..287S |doi=10.1038/479287a |pmid=22094671 |doi-access=free}}</ref> although it has been speculated to have played a role in an alleged much smaller extinction event at the Norian-Rhaetian boundary.<ref>{{Cite journal |last1=Sato |first1=Honami |last2=Ishikawa |first2=Akira |last3=Onoue |first3=Tetsuji |last4=Tomimatsu |first4=Yuki |last5=Rigo |first5=Manuel |date=30 December 2021 |title=Sedimentary record of Upper Triassic impact in the Lagonegro Basin, southern Italy: Insights from highly siderophile elements and Re-Os isotope stratigraphy across the Norian/Rhaetian boundary |url=https://www.sciencedirect.com/science/article/pii/S0009254121004496 |journal=[[Chemical Geology]] |volume=586 |pages=120506 |bibcode=2021ChGeo.58620506S |doi=10.1016/j.chemgeo.2021.120506 |issn=0009-2541 |s2cid=239637928 |access-date=26 November 2023}}</ref> The {{cvt|40|km}} wide [[Saint Martin crater]] in [[Manitoba]] has been proposed as a candidate for a possible TJME-causing impact, but its has since been dated to be Carnian.<ref>{{cite journal |last1=Schmieder |first1=Martin |last2=Jourdan |first2=Fred |last3=Tohver |first3=Eric |last4=Cloutis |first4=Edward A. |date=15 November 2014 |title=40Ar/39Ar age of the Lake Saint Martin impact structure (Canada) – Unchaining the Late Triassic terrestrial impact craters |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X14005445 |journal=[[Earth and Planetary Science Letters]] |volume=406 |pages=37–48 |bibcode=2014E&PSL.406...37S |doi=10.1016/j.epsl.2014.08.037 |access-date=30 May 2023}}</ref> Other putative or confirmed Triassic craters include the {{cvt|80|km}} wide [[Puchezh-Katunki crater]] in Eastern [[Russia]] (though it may be [[Jurassic]] in age), the {{cvt|15|km|0}} wide [[Obolon' crater]] in [[Ukraine]], and the {{cvt|9|km|0}} wide [[Red Wing crater|Red Wing Creek structure]] in [[North Dakota]]. Spray ''et al.'' (1998) noted an interesting phenomenon, that being how the Manicouagan, Rochechouart, and Saint Martin craters all seem to be at the same latitude, and that the Obolon' and Red Wing craters form parallel arcs with the Rochechouart and Saint Martin craters, respectively. Spray and his colleagues hypothesized that the Triassic experienced a "multiple impact event", a large fragmented asteroid or comet which broke up and impacted the earth in several places at the same time.<ref name=":4" /> Such an impact has been observed in the present day, when [[Comet Shoemaker–Levy 9|Comet Shoemaker-Levy 9]] broke up and hit Jupiter in 1992. However, the "multiple impact event" hypothesis for Triassic impact craters has not been well-supported; Kent (1998) noted that the Manicouagan and Rochechouart craters were formed in eras of different magnetic polarity,<ref>{{Cite journal |last=Kent |first=Dennis V. |date=10 September 1998 |title=Impacts on Earth in the Late Triassic |journal=[[Nature (journal)|Nature]] |volume=395 |issue=6698 |pages=126 |bibcode=1998Natur.395..126K |doi=10.1038/25874 |s2cid=4303109 |doi-access=free}}</ref> and radiometric dating of the individual craters has shown that the impacts occurred millions of years apart.<ref name="TannerLucas" />

[[Shocked quartz]] has been found in Rhaetian deposits from the [[Northern Apennines]] of Italy, providing possible evidence of an end-Triassic extraterrestrial impact.<ref>{{cite journal |last1=Bice |first1=D. M. |last2=Newton |first2=C. R. |last3=McCauley |first3=S. |last4=Reinerts |first4=P. W. |last5=McRoberts |first5=C. A. |date=24 January 1992 |title=Shocked Quartz at the Triassic-Jurassic Boundary in Italy |url=https://www.science.org/doi/10.1126/science.255.5043.443 |journal=[[Science (journal)|Science]] |volume=255 |issue=5043 |pages=443–446 |bibcode=1992Sci...255..443B |doi=10.1126/science.255.5043.443 |pmid=17842896 |s2cid=28314974 |access-date=30 May 2023}}</ref> Certain trace metals indicative of a [[bolide]] impact have been found in the late Rhaetian, though not at the Triassic-Jurassic boundary itself; the discoverers of these trace metal anomalies purport that such a bolide impact could only have been an indirect cause of the TJME.<ref>{{cite journal |last1=Hori |first1=Rie S. |last2=Fujiki |first2=Toru |last3=Inoue |first3=Eriko |last4=Kimura |first4=Jun-Ichi |date=9 February 2007 |title=Platinum group element anomalies and bioevents in the Triassic–Jurassic deep-sea sediments of Panthalassa |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018206004615 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=244 |issue=1–4 |pages=391–406 |bibcode=2007PPP...244..391H |doi=10.1016/j.palaeo.2006.06.038 |access-date=30 May 2023}}</ref> The discovery of [[seismites]] two to four metres thick coeval with the carbon isotope fluctuations associated with the TJME has been interpreted as evidence of a possible bolide impact, although no definitive link between these seismites and any impact event has been found.<ref>{{cite journal |last1=Simms |first1=Michael J. |date=1 June 2003 |title=Uniquely extensive seismite from the latest Triassic of the United Kingdom: Evidence for bolide impact? |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/6/557/192639/Uniquely-extensive-seismite-from-the-latest?redirectedFrom=fulltext |url-status=live |journal=[[Geology (journal)|Geology]] |volume=31 |issue=6 |pages=557{{ndash}}560 |bibcode=2003Geo....31..557S |doi=10.1130/0091-7613(2003)031<0557:UESFTL>2.0.CO;2 |archive-url=https://web.archive.org/web/20180602214717/https://pubs.geoscienceworld.org/gsa/geology/article-abstract/31/6/557/192639/uniquely-extensive-seismite-from-the-latest?redirectedFrom=fulltext |archive-date=2018-06-02 |access-date=31 May 2023}}</ref>

On the other hand, the dissimilarity between the isotopic perturbations characterising the TJME and those characterising the end-Cretaceous mass extinction makes an extraterrestrial impact highly unlikely to have been the cause of the TJME, according to many researchers.<ref>{{cite journal |last1=Ward |first1=Peter D. |last2=Garrison |first2=Geoffrey H. |last3=Haggart |first3=James W. |last4=Kring |first4=David A. |last5=Beattie |first5=Michael J. |date=15 August 2004 |title=Isotopic evidence bearing on Late Triassic extinction events, Queen Charlotte Islands, British Columbia, and implications for the duration and cause of the Triassic/Jurassic mass extinction |url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X04002857 |journal=[[Earth and Planetary Science Letters]] |volume=224 |issue=3–4 |pages=589–600 |bibcode=2004E&PSL.224..589W |doi=10.1016/j.epsl.2004.04.034 |access-date=23 November 2022}}</ref> Various trace metal ratios, including palladium/iridium, platinum/iridium, and platinum/rhodium, in rocks deposited during the TJME have numerical values very different from what would be expected in an extraterrestrial impact scenario, providing further evidence against this hypothesis.<ref name="PlatinumGroupElementsCAMP" /> The Triassic-Jurassic boundary furthermore lacks a fern spore spike akin to that observed at the terminus of the Cretaceous, inconsistent with an asteroid impact.<ref name="BonisEtAl2010">{{cite journal |last1=Bonis |first1=Nina R. |last2=Ruhl |first2=Micha |last3=Kürschner |first3=Wolfram R. |date=1 September 2010 |title=Milankovitch-scale palynological turnover across the Triassic–Jurassic transition at St. Audrie's Bay, SW UK |url=https://pubs.geoscienceworld.org/jgs/article/167/5/877/372819/Milankovitch-scale-palynological-turnover-across |journal=[[Journal of the Geological Society]] |volume=167 |issue=5 |pages=877–888 |bibcode=2010JGSoc.167..877B |doi=10.1144/0016-76492009-141 |s2cid=128896141 |access-date=12 December 2022}}</ref>