Editing Impact event (section)

===Earth impacts===
[[File:Artist's concept of collision at HD 172555.jpg|thumb|Artist's depiction of a collision between two planetary bodies. Such an impact between the Earth and a Mars-sized object likely [[giant impact theory|formed the Moon]].]]
In the early history of the Earth (about four billion years ago), bolide impacts were almost certainly common since the Solar System contained far more discrete bodies than at present. Such impacts could have included strikes by asteroids hundreds of kilometers in diameter, with explosions so powerful that they vaporized all the Earth's oceans. It was not until this heavy bombardment slackened that life appears to have begun to evolve on Earth.

====Precambrian====
The leading theory of the Moon's origin is the giant impact theory, which postulates that Earth was once hit by a [[Minor planet|planetoid]] the size of Mars; such a theory is able to explain the size and composition of the Moon, something not done by other theories of lunar formation.<ref>{{cite journal | title = Dynamics of Lunar Formation | author = Canup, Robin M. | journal = Annual Review of Astronomy & Astrophysics | volume = 42 | issue = 1 | pages = 441–475 | doi=10.1146/annurev.astro.41.082201.113457|bibcode = 2004ARA&A..42..441C | year = 2004 }}</ref>

According to the theory of the [[Late Heavy Bombardment]], there should have been 22,000 or more impact craters with diameters >20&nbsp;km (12&nbsp;mi), about 40 impact basins with diameters about 1,000&nbsp;km (620&nbsp;mi), and several impact basins with diameters about 5,000&nbsp;km (3,100&nbsp;mi). However, hundreds of millions of years of deformation at the Earth's crust pose significant challenges to conclusively identifying impacts from this period. Only two pieces of pristine [[lithosphere]] are believed to remain from this era: [[Kaapvaal craton]] (in contemporary South Africa) and [[Pilbara craton|Pilbara Craton]] (in contemporary Western Australia) to search within which may potentially reveal evidence in the form of physical craters. Other methods may be used to identify impacts from this period, for example, indirect gravitational or magnetic analysis of the mantle, but may prove inconclusive.

In 2021, evidence for a probable impact 3.46 billion-years ago at Pilbara Craton has been found in the form of a {{convert|150|km|mi}} crater created by the impact of a {{convert|10|km|mi}} asteroid (named "The Apex Asteroid") into the sea at a depth of {{convert|2.5|km|mi}} (near the site of [[Marble Bar, Western Australia]]).<ref name="Ohmoto Graham Liu Tsukamoto p.">{{citation | last1=Ohmoto | first1=Hiroshi | last2=Graham | first2=Uschi | last3=Liu | first3=Zi-Kui | last4=Tsukamoto | first4=Yuya | last5=Watanabe | first5=Yumiko | last6=Hamasaki | first6=Hiroshi | last7=Chorney | first7=Andrew | title=Discovery of a 3.46 billion-year-old impact crater in Western Australia | journal=Ess Open Archive ePrints | publisher=Wiley | date=2021-01-16 | volume=105 | doi=10.1002/essoar.10505838.1 | page=| bibcode=2021esoar.10505838O | s2cid=234265636 }}</ref> The event caused global tsunamis. It is also coincidental to some of the earliest evidence of life on Earth, fossilized [[Stromatolite]]s.

Evidence for at least 4 impact events have been found in spherule layers (dubbed S1 through S8)  from the [[Barberton Greenstone Belt]] in South Africa, spanning around 3.5-3.2 billion years ago.<ref>{{Cite journal |last1=Ozdemir |first1=Seda |last2=Schulz |first2=Toni |last3=Koeberl |first3=Christian |last4=Reimold |first4=Wolf Uwe |last5=Mohr-Westheide |first5=Tanja |last6=Hoehnel |first6=Desiree |last7=Schmitt |first7=Ralf Thomas |date=27 November 2017 |title=Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT 3 drill core |journal=Meteoritics & Planetary Science |language=en |volume=52 |issue=12 |pages=2586–2631 |doi=10.1111/maps.12998 |issn=1086-9379|doi-access=free |bibcode=2017M&PS...52.2586O }}</ref> The sites of the impacts are thought to have been distant from the location of the belt. The impactors that generated these events are thought to have been much larger than those that created the largest known still existing craters/impact structures on Earth, with the impactors having estimated diameters of ~{{Convert|20-50|km|mi}}, with the craters generated by these impacts having an estimated diameter of {{Convert|400-1000|km|mi}}.<ref>{{Cite journal |last1=Lowe |first1=Donald R. |last2=Byerly |first2=Gary R. |date=April 2018 |title=The terrestrial record of Late Heavy Bombardment |url=https://linkinghub.elsevier.com/retrieve/pii/S1387647317300714 |journal=New Astronomy Reviews |language=en |volume=81 |pages=39–61 |doi=10.1016/j.newar.2018.03.002|bibcode=2018NewAR..81...39L }}</ref> The largest impacts like those represented by the S2 layer are likely to have had far-reaching effects, such as the boiling of the surface layer of the oceans.<ref name="10.1073/pnas.2408721121PNAS">{{cite journal |last1=Drabon |first1=Nadja |last2=Knoll |first2=Andrew H. |last3=Lowe |first3=Donald R. |date=21 October 2024 |title=Effect of a giant meteorite impact on Paleoarchean surface environments and life. |journal=PNAS |volume=121 |issue=44 |pages= e2408721121|doi=10.1073/pnas.2408721121 |pmid=39432780 |pmc=11536127 }}</ref>

The [[Maniitsoq structure]], dated to around 3 billion years old (3 Ga), was once thought to be the result of an impact;<ref name="garde 2012">{{cite journal |last1=Garde |first1=Adam A. |last2=McDonald |first2=Iain |last3=Dyck |first3=Brendan |last4=Keulen |first4=Nynke |title=Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland |journal=Earth and Planetary Science Letters |date=July 2012 |volume=337–338 |pages=197–210 |doi=10.1016/j.epsl.2012.04.026|bibcode=2012E&PSL.337..197G }}</ref><ref name=":1">{{Cite journal|last=Wolf U. Reimold, Roger L. Gibson, Christian Koeberl|date=2013|title=Comment on "Searching for giant, ancient impact structures on Earth: The Mesoarchaean Maniitsoq structure, West Greenland" by Garde et al.|url=https://doi.org/10.1016/j.epsl.2013.04.014|journal=Earth and Planetary Science Letters|volume=369–370|pages=333–335|doi=10.1016/j.epsl.2013.04.014|via=Elsevier Science Direct}}</ref> however, follow-up studies have not confirmed its nature as an impact structure.<ref name=":1" /><ref name=":2">{{Cite journal|last=Wolf U. Reimold, Ludovic Ferrière, Alex Deutsch, Christian Koeberl|date=2014|title=Impact controversies: Impact recognition criteria and related issues|journal=Meteoritics and Planetary Science|volume=49|issue=5|pages=723–731|doi=10.1111/maps.12284|bibcode=2014M&PS...49..723R|s2cid=128625029|doi-access=free}}</ref><ref name=":3">{{Cite journal|last=C. L. Kirkland, C. Yakymchuk, J. Hollis, H. Heide-Jørgensen, M. Danišík|date=2018|title=Mesoarchean exhumation of the Akia terrane and a common Neoarchean tectonothermal history for West Greenland|journal=Precambrian Research|volume=314|pages=129–144|doi=10.1016/j.precamres.2018.06.004|bibcode=2018PreR..314..129K|s2cid=135213870|doi-access=free}}</ref><ref name=":5">{{Cite journal|last=N. J. Gardiner, C. L. Kirkland, J. Hollis, K. Szilas, A. Steenfelt, C. Yakymchuk, H. Heide-Jørgensen|date=2019|title=Building Mesoarchaean crust upon Eoarchaean roots: the Akia Terrane, West Greenland|journal=Contributions to Mineralogy and Petrology|volume=174|issue=3|page=20|doi=10.1007/s00410-019-1554-x|bibcode=2019CoMP..174...20G|s2cid=134027320|doi-access=free|hdl=10023/18486|hdl-access=free}}</ref><ref name=":6">{{Cite journal|last=C. Yakymchuk, C. L. Kirkland, J. A. Hollis, J. Kendrick, N. J. Gardiner, K. Szilas|date=2020|title=Mesoarchean partial melting of mafic crust and tonalite production during high-T–low-P stagnant tectonism, Akia Terrane, West Greenland|journal=Precambrian Research|volume=339|page=105615|doi=10.1016/j.precamres.2020.105615|bibcode=2020PreR..33905615Y|s2cid=213973363|doi-access=free|hdl=10023/19439|hdl-access=free}}</ref><ref name=":4">{{Cite journal|last=Pedro Waterton, William R. Hyde, Jonas Tusch, Julie A. Hollis, Christopher L. Kirkland, Carson Kinney, Chris Yakymchuk, Nicholas J. Gardiner, David Zakharov, Hugo K. H. Olierook, Peter C. Lightfoot, Kristoffer Szilas|date=2020|title=Geodynamic Implications of Synchronous Norite and TTG Formation in the 3 Ga Maniitsoq Norite Belt, West Greenland|journal=Frontiers in Earth Science|volume=8|page=562062|doi=10.3389/feart.2020.562062|bibcode=2020FrEaS...8..406W|doi-access=free|hdl=10023/20744|hdl-access=free}}</ref> The Maniitsoq structure is not recognised as an impact structure by the [[Earth Impact Database]].<ref name=":9">{{cite web|title=Earth Impact Database|url=http://www.passc.net/EarthImpactDatabase/New%20website_05-2018/Index.html|access-date=2020-09-30|website=www.passc.net}}</ref>

In 2020, scientists discovered the world's oldest confirmed impact crater, the [[Yarrabubba crater]], caused by an impact that occurred in [[Yilgarn craton]] (what is now [[Western Australia]]), dated at more than 2.2 billion years ago with the impactor estimated to be around {{convert|7|km|mi}} wide.<ref name="NYT-20200121">{{cite news |last=Kornel |first=Katherine |title=Earth's Oldest Asteroid Impact Found in Australia – The cataclysm, which occurred roughly 2.2 billion years ago, might have catapulted the planet out of an ice age. |url=https://www.nytimes.com/2020/01/21/science/oldest-asteroid-impact-australia.html |date=21 January 2020 |work=[[The New York Times]] |access-date=22 January 2020 }}</ref><ref name="NC-20200121">{{cite journal |author=Erikson, Timmons M. |display-authors=et al. |title=Precise radiometric age establishes Yarrabubba, Western Australia, as Earth's oldest recognised meteorite impact structure |date=21 January 2020 |journal=[[Nature Communications]] |volume=11 |issue=300 |page=300 |doi=10.1038/s41467-019-13985-7 |pmid=31964860 |pmc=6974607 |bibcode=2020NatCo..11..300E }}</ref><ref name=erickson>{{cite journal |author1=Erickson, T.M.|author2= Kirkland, C.L.|author3= Timms, N.E.|author4= Cavosie, A.J.|author5= Davison, T.M. |title=Precise radiometric age establishes Yarrabubba, Western Australia, as Earth's oldest recognised meteorite impact structure |journal=Nature Communications |date=21 Jan 2020 |volume=11 |issue=300 |page= 300|doi=10.1038/s41467-019-13985-7|pmid= 31964860|pmc= 6974607|bibcode=2020NatCo..11..300E }}</ref> It is believed that, at this time, the Earth was mostly or completely frozen, commonly called the [[Huronian glaciation]].

The [[Vredefort impact structure|Vredefort impact event]], which occurred around 2 billion years ago in [[Kaapvaal craton]] (what is now [[South Africa]]), caused the largest verified crater, a multi-ringed structure {{convert|160|-|300|km|mi|abbr=on|sigfig=1}} across, forming from an impactor approximately {{convert|10|–|15|km|abbr=on}} in diameter.<ref name="DB">{{Cite Earth Impact DB | name = Vredefort | access-date = 2008-12-30}}</ref><ref name="current record">{{cite web| title = Deep Impact – The Vredefort Dome| url=http://www.hartrao.ac.za/other/vredefort/vredefort.html| publisher= [[Hartebeesthoek Radio Astronomy Observatory]]| access-date = 2007-09-19| date = 2006-08-01}}</ref>

The [[Sudbury Basin|Sudbury impact event]] occurred on the [[Columbia (supercontinent)|Nuna supercontinent]] (now [[Canada]]) from a bolide approximately {{convert|10|-|15|km|mi|abbr=on}} in diameter approximately 1.849 billion years ago<ref name=Davis>{{cite journal|last=Davis| first= Donald W. | date= January 23, 2008| title= Sub-million-year age resolution of Precambrian igneous events by thermal extraction-thermal ionization mass spectrometer Pb dating of zircon: Application to crystallization of the Sudbury impact melt sheet| journal= Geology|  volume = 36| number = 5| pages= 383–386 |doi= 10.1130/G24502A.1| bibcode= 2008Geo....36..383D}}</ref> Debris from the event would have been scattered across the globe.

====Paleozoic and Mesozoic====
Two {{convert|10|km||adj=mid| sized}} asteroids are now believed to have struck Australia between 360 and 300 million years ago at the [[West Warburton Basin|Western Warburton]] and [[East Warburton Basin]]s, creating a {{convert|400|km||adj=mid| impact zone}}. According to evidence found in 2015, it is the largest ever recorded.<ref>{{Cite web|url=https://www.australiangeographic.com.au/news/2015/03/worlds-largest-asteroid-impact-found-in-australia/|title=World's largest asteroid impact found in Australia|date=March 24, 2015|website=Australian Geographic}}</ref> A [[Diamantina River ring feature|third, possible impact]] was also identified in 2015 to the north, on the upper [[Diamantina River]], also believed to have been caused by an asteroid 10&nbsp;km across about 300 million years ago, but further studies are needed to establish that this crustal anomaly was indeed the result of an impact event.<ref>{{cite web|url=http://www.ga.gov.au/news-events/news/latest-news/potential-asteroid-impact-identified-in-western-queensland|title=Potential asteroid impact identified in western Queensland|publisher=Geoscience Australia|access-date=26 June 2016|date=2015-03-17}}</ref>

[[File:Chicxulub-animation.gif|thumb|An animation modelling the impact, and subsequent crater formation of the Chicxulub impact (University of Arizona, Space Imagery Center)]]
The prehistoric [[Chicxulub crater#Impact specifics|Chicxulub impact]], 66 million years ago, believed to be the cause of the Cretaceous–Paleogene extinction event, was caused by an asteroid estimated to be about {{convert|10|km|mi}} wide.<ref name="autogenerated76"/>


==== Paleogene ====
[[File:Hiawatha v45 scene1 4k 5mtopo.1760.tif|thumb|The Hiawatha impact crater in Greenland is buried under more than a kilometre of ice]]
Analysis of the [[Hiawatha Glacier]] reveals the presence of a 31&nbsp;km wide impact crater dated at 58 million years of age, less than 10 million years after the Cretaceous–Paleogene extinction event, scientists believe that the impactor was a metallic asteroid with a diameter in the order of 1.5 kilometres (0.9&nbsp;mi). The impact would have had global effects.<ref name="InitialStudy">{{cite journal|first=Kurt H. |last=Kjær |display-authors=et al |doi=10.1126/sciadv.aar8173|pmid=30443592 |pmc=6235527 |title=A large impact crater beneath Hiawatha Glacier in northwest Greenland|journal=Science Advances |volume=4 |issue=11 |pages=eaar8173 |date=November 2018 |bibcode=2018SciA....4.8173K }}</ref>

==== Pleistocene ====
{{Further|Pleistocene}}
[[File:Barringer Crater aerial photo by USGS.jpg|thumb|Aerial view of [[Barringer Crater]] in [[Arizona]]]]

[[Stone tools|Artifacts]] recovered with [[tektites]] from the 803,000-year-old [[Australasian strewnfield]] event in Asia link a ''[[Homo erectus]]'' population to a significant meteorite impact and its aftermath.<ref>{{Cite web|url=http://humanorigins.si.edu/evidence/behavior/stone-tools/early-stone-age-tools/handaxe-and-tektites-bose-china|archiveurl=https://web.archive.org/web/20141008080600/https://humanorigins.si.edu/evidence/behavior/handaxe-and-tektites-bose-china|url-status=dead|title=Handaxe and Tektites from Bose, China|archivedate=October 8, 2014|website=The Smithsonian Institution's Human Origins Program}}</ref><ref>{{cite news| url=http://news.bbc.co.uk/2/hi/science/nature/664967.stm | work=BBC News | title=Asia's oldest axe tools discovered | date=March 3, 2000}}</ref><ref>{{Cite journal | doi=10.1146/annurev.anthro.33.070203.144024|title = Early Dispersals of Homo from Africa| journal=Annual Review of Anthropology| volume=33| pages=271–296|year = 2004|last1 = Antón|first1 = Susan C.| last2=Swisher, Iii| first2=Carl C.}}</ref> Significant examples of Pleistocene impacts include the [[Lonar crater lake]] in India, approximately 52,000 years old (though a study published in 2010 gives a much greater age), which now has a flourishing semi-tropical jungle around it.{{citation needed|date=February 2015}}
<!--The Younger Dryas impact hypothesis seems to be dead (2015) And, Younger Dryas is in Holocene, aka Modern Era --->

==== Holocene ====
{{Further|Holocene}}
The [[Rio Cuarto craters]] in Argentina were produced approximately 10,000 years ago, at the beginning of the Holocene. If proved to be impact craters, they would be the first impact of the Holocene.

The [[Campo del Cielo]] ("Field of Heaven") refers to an area bordering Argentina's [[Chaco Province]] where a group of iron meteorites were found, estimated as dating to 4,000–5,000 years ago. It first came to attention of Spanish authorities in 1576; in 2015, police arrested four alleged smugglers trying to steal more than a ton of protected meteorites.<ref>{{Cite web|url=http://news.yahoo.com/four-arrested-argentina-smuggling-more-ton-meteorites-210404348.html|title=Four arrested in Argentina smuggling more than ton of meteorites|website=news.yahoo.com}}</ref> The [[Henbury craters]] in Australia (~5,000 years old) and [[Kaali crater]]s in Estonia (~2,700 years old) were apparently produced by objects that broke up before impact.<ref>{{cite web | url=https://nt.gov.au/leisure/parks-reserves/find-a-park-to-visit/henbury-meteorites-conservation-reserve | title=Henbury Meteorites Conservation Reserve| date=2018-12-17}}</ref>{{citation needed|date=June 2018}}

[[Whitecourt crater]] in Alberta, Canada is estimated to be between 1,080 and 1,130 years old. The crater is approximately 36&nbsp;m (118&nbsp;ft) in diameter and 9&nbsp;m (30&nbsp;ft) deep, is heavily forested and was discovered in 2007 when a metal detector revealed fragments of meteoric iron scattered around the area.<ref>{{cite web |url=http://www.passc.net/EarthImpactDatabase/whitecourt.html |title=Whitecourt |access-date=2017-07-28 |archive-url=https://web.archive.org/web/20170718105534/http://www.passc.net/EarthImpactDatabase/whitecourt.html |archive-date=2017-07-18 |url-status=dead }}</ref><ref>{{cite web | url=http://www.whitecourtstar.com/2012/07/03/whitecourt-crater-attracts-visitors | archive-url=https://web.archive.org/web/20160305210537/http://www.whitecourtstar.com/2012/07/03/whitecourt-crater-attracts-visitors | url-status=dead | archive-date=2016-03-05 | title=Whitecourt Star }}</ref>

A Chinese record states that 10,000 people were killed in the 1490 [[Qingyang event]] with the deaths caused by a hail of "falling stones"; some astronomers hypothesize that this may describe an actual meteorite fall, although they find the number of deaths implausible.<ref>{{Citation | last1 = Yau | first1 = K. | last2 = Weissman | first2 = P. | last3 = Yeomans | first3 = D. | title = Meteorite Falls in China and Some Related Human Casualty Events | journal = Meteoritics | volume = 29 | issue = 6| pages = 864–871 | postscript = . | doi=10.1111/j.1945-5100.1994.tb01101.x | bibcode=1994Metic..29..864Y| year = 1994 }}</ref>

[[Kamil Crater]], discovered from [[Google Earth]] image review in [[Egypt]], {{convert|45|m|ft|abbr=on}} in diameter and {{convert|10|m|ft|abbr=on}} deep, is thought to have been formed less than 3,500 years ago in a then-unpopulated region of western Egypt. It was found February 19, 2009 by V. de Michelle on a Google Earth image of the East Uweinat Desert, Egypt.<ref>USGS Meteoritical Society, Bulletin database, Gebel Kamil Crater ... http://www.lpi.usra.edu/meteor/metbull.php?code=52031</ref>

====20th-century impacts====
[[File:Tunguska Ereignis-1.jpg|thumb|Trees knocked over by the [[Tunguska event|Tunguska blast]]]]

One of the best-known recorded impacts in modern times was the Tunguska event, which occurred in [[Siberia]], Russia, in 1908.<ref>{{cite web|title=Tunguska event {{!}} Summary, Cause, & Facts|url=https://www.britannica.com/event/Tunguska-event|access-date=2021-09-25|website=Encyclopedia Britannica|language=en}}</ref> This incident involved an explosion that was probably caused by the airburst of an asteroid or comet {{convert|5|to|10|km|mi|abbr=on}} above the Earth's surface, [[felling]] an estimated 80 million trees over {{convert|2150|km2|mi2|0|abbr=on}}.<ref>{{cite web|url=http://www.bbc.com/earth/story/20160706-in-siberia-in-1908-a-huge-explosion-came-out-of-nowhere|title=In Siberia in 1908, a huge explosion came out of nowhere|last=Hogenboom|first=Melissa|access-date=2017-03-30}}</ref>

In February 1947, another large bolide impacted the Earth in the [[Sikhote-Alin Mountains]], [[Primorsky Krai|Primorye]], Soviet Union. It was during daytime hours and was witnessed by many people, which allowed [[V. G. Fesenkov]], then chairman of the meteorite committee of the USSR Academy of Science, to estimate the meteoroid's orbit before it encountered the Earth. [[Sikhote-Alin meteorite|Sikhote-Alin]] is a massive fall with the overall size of the [[meteoroid]] estimated at {{convert|90000|kg|lb|abbr=on}}. A more recent estimate by Tsvetkov (and others) puts the mass at around {{convert|100000|kg|lb|abbr=on}}.<ref name="metmag">{{cite journal |url=http://meteoritemag.uark.edu/604.htm |journal=Meteorite Magazine | date=February 1996 |title=Sikhote-Alin Revisited |first=Roy |last=Gallant |volume=2 |page=8 |bibcode=1996Met.....2....8G |archive-url=https://web.archive.org/web/20100612144717/http://meteoritemag.uark.edu/604.htm |archive-date=2010-06-12 |url-status=dead }}</ref> It was an iron meteorite belonging to the chemical group IIAB and with a coarse octahedrite structure. More than 70 [[tonne]]s ([[metric ton]]s) of material survived the collision.

A case of a human injured by a space rock occurred on November 30, 1954, in [[Sylacauga, Alabama]].<ref>[http://imca.repetti.net/metinfo/metstruck.html Meteorite Hits Page] {{webarchive |url=https://web.archive.org/web/20090831183851/http://imca.repetti.net/metinfo/metstruck.html |date=August 31, 2009 }}</ref> There a {{convert|4|kg|lb|abbr=on}} stone chondrite crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She was badly bruised by the [[Hodges Meteorite#Fragments|fragments]]. Several persons have since claimed to have been struck by "meteorites" but no verifiable meteorites have resulted.

A small number of [[meteorite fall]]s have been observed with automated cameras and recovered following calculation of the impact point. The first was the [[Příbram meteorite]], which fell in Czechoslovakia (now the Czech Republic) in 1959.<ref>{{Citation |last=Ceplecha |first=Z. |date=1961 |title=Multiple fall of Příbram meteorites photographed |journal=Bull. Astron. Inst. Czechoslovakia |volume=12 |pages=21–46 |bibcode=1961BAICz..12...21C }}</ref> In this case, two cameras used to photograph meteors captured images of the fireball. The images were used both to determine the location of the stones on the ground and, more significantly, to calculate for the first time an accurate orbit for a recovered meteorite.

Following the Příbram fall, other nations established automated observing programs aimed at studying infalling meteorites.<ref>Gritsevich, M.I. The Pribram, Lost City, Innisfree, and Neuschwanstein falls: An analysis of the atmospheric trajectories. Sol Syst Res 42, 372–390 (2008). https://doi.org/10.1134/S003809460805002X</ref> One of these was the [[Prairie Meteorite Network]], operated by the [[Smithsonian Astrophysical Observatory]] from 1963 to 1975 in the midwestern U.S. This program also observed a meteorite fall, the "Lost City" chondrite, allowing its recovery and a calculation of its orbit.<ref>{{Citation |last1=McCrosky |first1=R. E. |last2=Posen |first2=A. |last3=Schwartz |first3=G. |last4=Shao |first4=C. Y. |date=1971 |title=Lost City meteorite: Its recovery and a comparison with other fireballs |journal=J. Geophys. Res. |volume=76 |issue= 17|pages=4090–4108 |doi=10.1029/JB076i017p04090 |bibcode=1971JGR....76.4090M|hdl=2060/19710010847 |s2cid=140675097 |hdl-access=free }}</ref> Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, "Innisfree", in 1977.<ref>{{Citation |last1=Campbell-Brown |first1=M. D. |last2=Hildebrand |first2=A. |date=2005 |title=A new analysis of fireball data from the Meteorite Observation and Recovery Project (MORP) |journal=Earth, Moon, and Planets |volume=95 |issue=1–4 |pages=489–499 |doi=10.1007/s11038-005-0664-9 |bibcode = 2004EM&P...95..489C |s2cid=121255827 }}</ref> Finally, observations by the European Fireball Network, a descendant of the original Czech program that recovered Příbram, led to the discovery and orbit calculations for the [[Neuschwanstein]] meteorite in 2002.<ref>{{Citation |last1=Oberst |first1=J. |date=2004 |title=The multiple meteorite fall of Neuschwanstein: Circumstances of the event and meteorite search campaigns |journal=[[Meteoritics & Planetary Science]] |volume=39 |issue=10 |pages=1627–1641 |doi=10.1111/j.1945-5100.2004.tb00062.x |bibcode=2004M&PS...39.1627O |display-authors=2 |last2=Heinlein |first2=D. |last3=Spurný |first3=P.|doi-access=free }}</ref>

On August 10, 1972, a meteor which became known as the [[1972 Great Daylight Fireball]] was witnessed by many people as it moved north over the [[Rocky Mountains]] from the U.S. Southwest to Canada. It was filmed by a tourist at the [[Grand Teton National Park]] in [[Wyoming]] with an 8-millimeter color movie camera.<ref>{{YouTube|7M8LQ7_hWtE|Grand Teton Meteor Video}}</ref> In size range the object was roughly between a car and a house, and while it could have ended its life in a Hiroshima-sized blast, there was never any explosion. Analysis of the trajectory indicated that it never came much lower than {{convert|58|km|mi|0|abbr=on}} off the ground, and the conclusion was that it had grazed Earth's atmosphere for about 100 seconds, then skipped back out of the atmosphere and returned to its orbit around the Sun.

Many impact events occur without being observed by anyone on the ground. Between 1975 and 1992, American missile [[early warning satellite]]s picked up 136 major explosions in the upper atmosphere.<ref>{{Cite web|url=http://www.aerospaceweb.org/question/astronomy/q0296.shtml|title= Collisions with Near Earth Objects|website=www.aerospaceweb.org}}</ref> In the November 21, 2002, edition of the journal ''Nature'', Peter Brown of the University of Western Ontario reported on his study of U.S. early warning satellite records for the preceding eight years. He identified 300 flashes caused by {{convert|1|to|10|m|ft|0|abbr=on}} meteors in that time period and estimated the rate of Tunguska-sized events as once in 400 years.<ref>[https://archive.today/20120910052024/http://www.spaceref.com/news/viewpr.html?pid=9865 Satellite Study Establishes Frequency of Megaton-sized Asteroid Impacts] (SpaceRef November 20, 2002)</ref> [[Eugene Shoemaker]] estimated that an event of such magnitude occurs about once every 300 years, though more recent analyses have suggested he may have overestimated by an order of magnitude.

In the dark morning hours of January 18, 2000, a [[Tagish Lake (meteorite)|fireball]] exploded over the city of [[Whitehorse, Yukon Territory]] at an altitude of about {{convert|26|km|mi|0|abbr=on}}, lighting up the night like day. The meteor that produced the fireball was estimated to be about {{convert|4.6|m|ft|abbr=on}} in diameter, with a weight of 180 tonnes. This blast was also featured on the Science Channel series ''Killer Asteroids'', with several witness reports from residents in [[Atlin, British Columbia]].

==== 21st-century impacts ====
{{main|List of bolides}}
<!-- DDMMYYYY sequence Put 21st-c. discoveries of earlier earth impacts under appropriate heading  -->
On 7 June 2006, a meteor was observed striking a location in the [[Reisadalen]] valley in [[Nordreisa Municipality]] in [[Troms]] County, Norway. Although initial witness reports stated that the resultant fireball was equivalent to [[Atomic bombings of Hiroshima and Nagasaki|the Hiroshima nuclear explosion]], scientific analysis places the force of the blast at anywhere from 100 to 500 [[tonne#Use of mass as proxy for energy|tonnes]] TNT equivalent, around three percent of Hiroshima's yield.<ref>[https://archive.today/20120629002618/http://skyandtelescope.com/news/article_1742_1.asp Norway Impact Gentler Than Atomic Bomb] (Sky & Telescope June 16, 2006)</ref>

On 15 September 2007, a chondritic [[Carancas impact event|meteor crashed near the village of Carancas]] in southeastern Peru near [[Lake Titicaca]], leaving a water-filled hole and spewing gases across the surrounding area. Many residents became ill, apparently from the noxious gases shortly after the impact.

On 7 October 2008, an approximately 4 meter asteroid labeled {{mpl|2008 TC|3}} was tracked for 20 hours as it approached Earth and as it fell through the atmosphere and impacted in Sudan. This was the first time an object was detected before it reached the atmosphere and hundreds of pieces of the meteorite were recovered from the [[Nubian Desert]].<ref>[https://www.wired.com/wiredscience/2009/03/meteorite/ First-Ever Asteroid Tracked From Space to Earth], Wired, March 25, 2009 {{webarchive |url=https://web.archive.org/web/20140321060157/http://www.wired.com/wiredscience/2009/03/meteorite/ |date=March 21, 2014 }}</ref>

[[File:Chelyabinsk meteor trace 15-02-2013.jpg|thumb|Trail left by the exploding Chelyabinsk meteor as it passed over the city.]]

On 15 February 2013, an asteroid entered Earth's atmosphere over [[Russia]] as a [[Bolide|fireball]] and exploded above the city of [[Chelyabinsk]] during its passage through the [[Ural (region)|Ural Mountains region]] at 09:13 [[Yekaterinburg Time|YEKT]] (03:13 [[Coordinated Universal Time|UTC]]).<ref name=meteor>{{cite web|title=Russian Meteor|url=http://www.nasa.gov/topics/solarsystem/features/russianmeteor.html|publisher=NASA|access-date=15 February 2013|archive-date=18 February 2013|archive-url=https://web.archive.org/web/20130218034325/http://www.nasa.gov/topics/solarsystem/features/russianmeteor.html|url-status=dead}}</ref><ref>{{cite news|url=https://www.usatoday.com/story/news/world/2013/02/15/russia-meteorite/1921991/ |title=Meteor in central Russia injures at least 500 |work=[[USA Today]] |access-date=15 February 2013 |first1=Anna |last1=Arutunyan |first2=Marc |last2=Bennetts |date=15 February 2013}}</ref> The object's air burst occurred at an altitude between {{convert|30|and|50|km|mi|abbr=on}} above the ground,<ref>{{cite news |title=Meteor falls in Russia, 700 injured by blasts |url=http://bigstory.ap.org/article/meteorite-falls-russian-urals |agency=Associated Press |access-date=15 February 2013 |archive-date=18 February 2013 |archive-url=https://web.archive.org/web/20130218034039/http://bigstory.ap.org/article/meteorite-falls-russian-urals |url-status=dead }}</ref> and about 1,500 people were injured, mainly by broken window glass shattered by the shock wave. Two were reported in serious condition; however, there were no fatalities.<ref name="chelyabinsk">{{cite web |url=http://www.vesti.ru/doc.html?id=1033922|script-title=ru:Метеоритный дождь над Уралом: пострадали 1200 человек |language= ru |work= Vesti |date=15 February 2013|access-date=15 February 2013 | location = [[Russia|RU]]}}</ref> Initially some 3,000 buildings in six cities across the region were reported damaged due to the explosion's shock wave, a figure which rose to over 7,200 in the following weeks.<ref>{{cite news|last=Marson|first=James|title=Meteorite Hits Russia, Causing Panic|url=https://www.wsj.com/articles/SB10001424127887324162304578305163574597722?mod=WSJ_hpp_LEFTTopStories|newspaper=Wall Street Journal|access-date=15 February 2013|author2=Gautam Naik}}</ref><ref>{{cite magazine|last=Ewait|first=David|title=Exploding Meteorite Injures A Thousand People In Russia|url=https://www.forbes.com/sites/davidewalt/2013/02/15/exploding-meteorite-injures-a-thousand-people-in-russia/|magazine=Forbes|access-date=15 February 2013}}</ref> The Chelyabinsk meteor was estimated to have caused over $30 million in damage.<ref>{{cite news|url=http://in.reuters.com/article/russia-meteorite-idINDEE91E03320130215|title=Meteorite explodes over Russia, more than 1,000 injured|author=Andrey Kuzmin|work=Reuters|date=16 February 2013|access-date=16 February 2013|archive-date=6 March 2016|archive-url=https://web.archive.org/web/20160306214917/http://in.reuters.com/article/russia-meteorite-idINDEE91E03320130215|url-status=dead}}</ref><ref name="RBTH-23513">{{cite news | url=http://rbth.ru/news/2013/03/05/meteorite-caused_emergency_situation_regime_over_in_chelyabinsk_region_23513.html | title=Meteorite-caused emergency situation regime over in Chelyabinsk region | work=Russia Beyond The Headlines | publisher=Rossiyskaya Gazeta | date=5 March 2013 | agency=[[Interfax]] | access-date=6 March 2013 | archive-date=23 June 2013 | archive-url=https://archive.today/20130623230931/http://rbth.ru/news/2013/03/05/meteorite-caused_emergency_situation_regime_over_in_chelyabinsk_region_23513.html | url-status=dead }}</ref> It is the largest recorded object to have encountered the Earth since the 1908 Tunguska event.<ref>{{cite news|url=https://www.economist.com/blogs/babbage/2013/02/asteroid-impacts?fsrc=nlw%7Cnewe%7C2-15-2013%7C5019506%7C37104620%7C|title=Asteroid impacts – How to avert Armageddon
 |newspaper=[[The Economist]] |date=15 February 2013|access-date=16 February 2013}}</ref><ref>{{cite news|url=https://www.nytimes.com/2013/02/16/science/space/size-of-blast-and-number-of-injuries-are-seen-as-rare-for-a-rock-from-space.html?ref=science&_r=0|title=Size of Blast and Number of Injuries Are Seen as Rare for a Rock From Space|author=Kenneth Chang|work=[[The New York Times]]|date=15 February 2013|access-date=16 February 2013}}</ref> The meteor is estimated to have an initial diameter of 17–20 metres and a mass of roughly 10,000 tonnes. On 16 October 2013, a team from Ural Federal University led by Victor Grokhovsky recovered a large fragment of the meteor from the bottom of Russia's Lake Chebarkul, about 80&nbsp;km west of the city.<ref>{{cite magazine|last=Beatty|first=J. Kelly|title=Russian Fireball Fragment Found|magazine=Australian Sky & Telescope|date=February–March 2014|page=12|issn=1832-0457}}</ref>

On 1 January 2014, a 3-meter (10 foot) asteroid, [[2014 AA]] was discovered by the [[Mount Lemmon Survey]] and observed over the next hour, and was soon found to be on a collision course with Earth. The exact location was uncertain, constrained to a line between [[Panama]], the central Atlantic Ocean, [[The Gambia]], and Ethiopia. Around roughly the time expected (2 January 3:06 UTC) an infrasound burst was detected near the center of the impact range, in the middle of the Atlantic Ocean.<ref name="Farnocchia2016">{{cite journal|title=The trajectory and atmospheric impact of asteroid 2014 AA|first1=Davide|last1=Farnocchia|first2=Steven R.|last2=Chesley|first3=Peter G.|last3=Brown|first4=Paul W.|last4=Chodas|date=1 August 2016|journal=[[Icarus (journal)|Icarus]]|volume=274|pages=327–333|bibcode=2016Icar..274..327F|doi=10.1016/j.icarus.2016.02.056 }}</ref><ref name="Marcos2016">{{cite journal|title=Homing in for New Year: impact parameters and pre-impact orbital evolution of meteoroid 2014 AA|first1=C.|last1=de la Fuente Marcos|first2=R.|last2=de la Fuente Marcos|first3=P.|last3=Mialle|date=13 October 2016|journal=[[Astrophysics and Space Science]]|volume=361|issue=11|pages=358 (33 pp.)|arxiv=1610.01055|bibcode=2016Ap&SS.361..358D |doi=10.1007/s10509-016-2945-3|s2cid=119251345}}</ref> This marks the second time a natural object was identified prior to impacting earth after 2008 TC3.

Nearly two years later, on October 3, [[WT1190F]] was detected orbiting Earth on a highly eccentric orbit, taking it from well within the [[Geocentric orbit|Geocentric satellite ring]] to nearly twice the orbit of the Moon. It was estimated to be perturbed by the Moon onto a collision course with Earth on November 13. With over a month of observations, as well as precovery observations found dating back to 2009, it was found to be far less dense than a natural asteroid should be, suggesting that it was most likely an unidentified artificial satellite. As predicted, it fell over [[Sri Lanka]] at 6:18 UTC (11:48 local time). The sky in the region was very overcast, so only an airborne observation team was able to successfully observe it falling above the clouds. It is now thought to be a remnant of the [[Lunar Prospector]] mission in 1998, and is the third time any previously unknown object – natural or artificial – was identified prior to impact.

On 22 January 2018, an object, [[A106fgF]], was discovered by the [[Asteroid Terrestrial-impact Last Alert System]] (ATLAS) and identified as having a small chance of impacting Earth later that day.<ref>[https://groups.yahoo.com/neo/groups/mpml/conversations/messages/33680 Bill Gray MPML]{{dead link|date=December 2023|bot=medic}}{{cbignore|bot=medic}}</ref> As it was very dim, and only identified hours before its approach, no more than the initial 4 observations covering a 39-minute period were made of the object. It is unknown if it impacted Earth or not, but no fireball was detected in either infrared or infrasound, so if it did, it would have been very small, and likely near the eastern end of its potential impact area – in the western Pacific Ocean.

On 2 June 2018, the [[Mount Lemmon Survey]] detected {{mpl|2018 LA}} (ZLAF9B2), a small 2–5 meter asteroid which further observations soon found had an 85% chance of impacting Earth. Soon after the impact, a fireball report from [[Botswana]] arrived to the [[American Meteor Society]]. Further observations with ATLAS extended the observation arc from 1 hour to 4 hours and confirmed that the asteroid orbit indeed impacted Earth in southern Africa, fully closing the loop with the fireball report and making this the third natural object confirmed to impact Earth, and the second on land after {{mp|2008 TC|3}}.<ref name="orientation">{{cite journal
|last1=de la Fuente Marcos |first1=Carlos
|last2=de la Fuente Marcos |first2=Raúl
|date=18 June 2018
|title=On the Pre-impact Orbital Evolution of 2018 LA, Parent Body of the Bright Fireball Observed Over Botswana on 2018 June 2
|journal=[[Research Notes of the AAS]]
|volume=2
|issue=2
|page=57
|arxiv=1806.05164
|bibcode=2018RNAAS...2...57D
|doi=10.3847/2515-5172/aacc71|s2cid=119325928
|doi-access=free
}}</ref><ref name="pre-impact2">{{cite journal
|last1=de la Fuente Marcos |first1=Carlos
|last2=de la Fuente Marcos |first2=Raúl
|date=26 July 2018
|title=Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update
|journal=[[Research Notes of the AAS]]
|volume=2
|issue=3
|page=131
|arxiv=1807.08322
|bibcode=2018RNAAS...2..131D
|doi=10.3847/2515-5172/aad551|s2cid=119208392
|doi-access=free
}}</ref><ref name="excess">{{cite journal |last1=de la Fuente Marcos |first1=C. |last2=de la Fuente Marcos | first2= R.|title=Waiting to make an impact: A probable excess of near-Earth asteroids in 2018 LA-like orbits |journal=[[Astronomy and Astrophysics]] |volume= 621|pages= A137|date=2019 |doi=10.1051/0004-6361/201834313
 |arxiv=1811.11845 |bibcode=2019A&A...621A.137D|s2cid=119538516 }}</ref>

On 8 March 2019, [[NASA]] announced the detection of a large airburst that occurred on 18 December 2018 at 11:48 local time off the eastern coast of the [[Kamchatka Peninsula]]. The [[Kamchatka superbolide]] is estimated to have had a mass of roughly 1600 tons, and a diameter of 9 to 14 meters depending on its density, making it the third largest asteroid to impact Earth since 1900, after the Chelyabinsk meteor and the Tunguska event. The fireball exploded in an airburst {{convert|25.6|km|mi}} above Earth's surface.

[[2019 MO]], an approximately 4m asteroid, was detected by [[Asteroid Terrestrial-impact Last Alert System|ATLAS]] a few hours before it impacted the Caribbean Sea near Puerto Rico in June 2019.<ref>{{Cite web |date=25 June 2019 |title=Breakthrough: UH team successfully locates incoming asteroid |url=https://legacy.ifa.hawaii.edu/info/press-releases/ATLAS_2019MO/ |access-date=12 March 2023 |website=Institute for Astronomy – University of Hawaii}}</ref>

In 2023, a small meteorite is believed to have crashed through the roof of a home in Trenton, New Jersey. The metallic rock was approximately 4 inches by 6 inches and weighed 4 pounds. The item was seized by police and tested for radioactivity.<ref>{{Cite web |url=https://apnews.com/article/meteorite-hits-home-hopewell-new-jersey-fd8391f8c5daea1e596ed85ed3ae5a68 |title=Possible meteorite crashes into New Jersey home, no injuries |date=May 9, 2023 |publisher=[[AP News]] |access-date=May 10, 2023}}</ref> The object was later confirmed to be a meteorite by scientists at The College of New Jersey, as well as meteorite expert Jerry Delaney, who previously worked at Rutgers University and the American Museum of Natural History.<ref>{{Cite web |url=https://apnews.com/article/meteorite-hits-home-hopewell-new-jersey-91fecf2eb7e5ffb938bfb68920dc6011 |title=Experts: Metallic object that crashed into New Jersey home was a meteorite |date=May 11, 2023 |publisher=[[AP News]] |access-date=May 14, 2023}}</ref>

===== Asteroid impact prediction =====
{{main|Asteroid impact prediction}}

[[File:2018 LA-orbit.png|thumb|250px|[[Orbit]] and positions of [[2018 LA]] and Earth, 30 days before impact. The diagram illustrates how orbit data can be used to predict impacts well in advance. Note that in this particular instance the asteroid's orbit was not known until a few hours before impact. The diagram was constructed afterwards for illustration.]]

In the late 20th and early 21st century scientists put in place measures to detect [[Near Earth object]]s, and predict the dates and times of [[asteroids]] impacting Earth, along with the locations at which they will impact. The [[International Astronomical Union]] [[Minor Planet Center]] (MPC) is the global clearing house for information on asteroid orbits. [[NASA]]'s [[Sentry (monitoring system)|Sentry System]] continually scans the MPC catalog of known asteroids, analyzing their orbits for any possible future impacts.<ref>{{YouTube|id=53Js-_vo3mo|title=How Does NASA Spot a Near-Earth Asteroid?}}</ref> Currently none are predicted (the single highest probability impact currently listed is ~7 m asteroid {{mpl|2010 RF|12}}, which is due to pass earth in September 2095 with only a 5% predicted chance of impacting).<ref>{{cite web|title=Sentry: Earth Impact Monitoring|url=https://cneos.jpl.nasa.gov/sentry/|website=Jet Propulsion Laboratory|publisher=NASA|access-date=25 August 2018}}</ref>

Currently prediction is mainly based on cataloging [[asteroids]] years before they are due to impact. This works well for larger asteroids (> 1 [[kilometre|km]] across) as they are easily seen from a long distance. Over 95% of them are already known and their [[orbit]]s have been measured, so any future impacts can be predicted long before they are on their final approach to Earth. Smaller objects are too faint to observe except when they come very close and so most cannot be observed before their final approach. Current mechanisms for detecting asteroids on final approach rely on wide-field ground based [[telescopes]], such as the ATLAS system. However, current telescopes only cover part of the Earth and even more importantly cannot detect asteroids on the day-side of the planet, which is why so few of the smaller asteroids that commonly impact Earth are detected during the few hours that they would be visible.<ref name="JPL-2017-SDT-Update">{{cite news
  |title      = Update to Determine the Feasibility of Enhancing the Search and Characterization of NEOs
  |work       = Near-Earth Object Science Definition Team Report 2017
  |publisher  = NASA
  |url        = https://www.nasa.gov/sites/default/files/atoms/files/2017_neo_sdt_final_e-version.pdf
  |access-date = 7 July 2018}}</ref>
So far only four impact events have been successfully predicted, all from innocuous 2–5 m diameter asteroids and detected a few hours in advance.

{{wide image|SmallAsteroidImpacts-Frequency-Bolide-20141114.jpg|500px|align-cap=center|Ground based telescopes can only detect objects approaching on the night-side of the planet, away from the [[Sun]]. Roughly half of impacts occur on the day-side of the planet.}}