Editing Extinction event (section)

====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>