{{location map| North America|relief=1|float=right|width=250|caption=Location of Chicxulub crater, Mexico| lat=21.4|long=-89.5}}
[[Image:Yucatan chix crater.jpg|thumb|300px|Imaging from [[NASA]]'s Shuttle Radar Topography Mission [[STS-99]] reveals part of the {{convert|180|km|abbr=on}} diameter ring of the crater. The numerous [[sinkhole]]s clustered around the trough of the crater suggest a prehistoric [[oceanic basin]] in the depression left by the impact.<ref name="NASA PIA03379">{{cite web|title=PIA03379: Shaded Relief with Height as Color, Yucatan Peninsula, Mexico|url=http://photojournal.jpl.nasa.gov/catalog/PIA03379|work=[[Shuttle Radar Topography Mission]]|publisher=[[NASA]]|accessdate=October 28, 2010}}</ref>]]
The '''Chicxulub crater''' ({{IPAc-en|pron|ˈ|tʃ|iː|k|ʃ|ᵿ|l|uː|b}}; {{IPA-myn|tʃʼikʃuluɓ|lang}}) is an [[impact crater]] buried underneath the [[Yucatán Peninsula]] in [[Mexico]].<ref>{{Cite Earth Impact DB | name = Chicxulub | accessdate = December 30, 2008 }}</ref> Its center is located near the town of [[Chicxulub, Yucatán|Chicxulub]], after which the crater is named.<ref name=penfield /> It was formed by a large [[asteroid]] or [[comet]] about 10 to 15 kilometres (6 to 9 miles) in diameter,<ref name="science" /><ref>[http://www.bbc.com/news/science-environment-39922998 BBC news report 15 May 2017]</ref> the [[Chicxulub impactor]], striking the Earth. The date of the impact coincides precisely with the [[Cretaceous–Paleogene boundary]] (K–Pg boundary), slightly less than 66 million years ago,<ref>Renne et al.</ref> and a widely accepted theory is that worldwide climate disruption from the event was the cause of the [[Cretaceous–Paleogene extinction event]], a [[mass extinction]] in which 75% of plant and animal species on Earth suddenly became extinct, including all non-[[bird|avian]] [[dinosaur]]s. The crater is more than {{convert|180|km|abbr=off|sp=us}} in diameter and {{convert|20|km|abbr=on}} in depth, well into the [[continental crust]] of the region of about 10–30 km depth. It makes the feature the third of the [[List of impact craters on Earth#Confirmed impact craters listed by size|largest confirmed impact structures on Earth]].
The crater was discovered by Antonio Camargo and Glen Penfield, [[geophysics|geophysicists]] who had been looking for [[petroleum]] in the Yucatán during the late 1970s. Penfield was initially unable to obtain evidence that the geological feature was a crater and gave up his search. Later, through contact with Alan Hildebrand in 1990, Penfield obtained samples that suggested it was an impact feature. Evidence for the impact origin of the crater includes [[shocked quartz]],<ref name="Becker2002">{{cite journal | first1=Luann | last1=Becker | url=http://www.miracosta.edu/home/kmeldahl/articles/blows.pdf | title=Repeated Blows | accessdate=January 28, 2016 | journal=Scientific American | year=2002 | volume=286 | issue=3 | pages=76–83| bibcode=2002SciAm.286c..76B | doi=10.1038/scientificamerican0302-76 | pmid=11857903 }}</ref> a [[gravity anomaly]], and [[tektite]]s in surrounding areas.
==Discovery==
[[Image:Chicxulub-Anomaly.jpg|thumb|[[Gravity anomaly]] map of the Chicxulub impact structure. The coastline is shown as a white line. A striking series of [[concentric]] features reveals the location of the crater. White dots represent water-filled [[sinkhole]]s (solution-collapse features common in the limestone rocks of the region) called ''cenotes'' after the Maya word ''dzonot''. A dramatic ring of cenotes is associated with the largest peripheral gravity-gradient feature. The origin of the cenote ring remains uncertain, although the link to the underlying buried crater seems clear.]]
In 1978, geophysicists Glen Penfield and Antonio Camargo were working for the Mexican state-owned oil company [[Pemex|Petróleos Mexicanos]], or Pemex, as part of an airborne magnetic survey of the [[Gulf of Mexico]] north of the Yucatán peninsula.<ref name=verschuur>Verschuur, 20–21.</ref> Penfield's job was to use geophysical data to scout possible locations for oil drilling.<ref name=bates>Bates.</ref> In the data, Penfield found a huge underwater arc with "extraordinary symmetry" in a ring {{convert|70|km|abbr=on|-1}} across.<ref name=penfield>Penfield.</ref> He then obtained a [[Gravity anomaly|gravity map]] of the Yucatán made in the 1960s. A decade earlier, the same map suggested an impact feature to contractor Robert Baltosser, but he was forbidden to publicize his conclusion by Pemex corporate policy of the time.<ref>Verschuur, 20.</ref> Penfield found another arc on the peninsula itself, the ends of which pointed northward. Comparing the two maps, he found the separate arcs formed a circle, {{convert|180|km|abbr=on}} wide, centered near the Yucatán village [[Chicxulub, Yucatán|Chicxulub]]; he felt certain the shape had been created by a cataclysmic event in geologic history.
Pemex disallowed release of specific data but let Penfield and company official Antonio Camargo present their results at the 1981 [[Society of Exploration Geophysicists]] conference.<ref>Weinreb.</ref> That year's conference was underattended and their report attracted scant attention. Coincidentally, many experts in [[impact crater]]s and the [[Cretaceous–Paleogene boundary|K–Pg boundary]] were attending a separate conference on Earth impacts. Although Penfield had plenty of geophysical data sets, he had no rock cores or other physical evidence of an impact.<ref name=bates/>
He knew Pemex had drilled exploratory wells in the region. In 1951, one bored into what was described as a thick layer of [[andesite]] about {{convert|1.3|km|ft}} down. This layer could have resulted from the intense heat and pressure of an Earth impact, but at the time of the borings it was dismissed as a [[lava dome]]—a feature uncharacteristic of the region's geology. Penfield tried to secure site samples, but was told such samples had been lost or destroyed.<ref name=bates/> When attempts at returning to the drill sites and looking for rocks proved fruitless, Penfield abandoned his search, published his findings and returned to his Pemex work.
[[Image:Chicxulub shockedquartz.png|thumb|left|Penfield with the sample of [[shocked quartz]] found at Well #2, Chicxulub]]
At the same time, in 1980, geologist [[Walter Alvarez]] and his father, Nobel Prize-winning scientist [[Luis Walter Alvarez]], put forth [[Alvarez hypothesis|his hypothesis]] that a large extraterrestrial body had struck Earth. In 1981, unaware of Penfield's discovery, [[University of Arizona]] graduate student Alan R. Hildebrand and faculty adviser William V. Boynton published a draft Earth-impact theory and sought a candidate crater.<ref>Mason.</ref> Their evidence included greenish-brown clay with surplus [[iridium]] containing [[shocked quartz]] grains and small weathered [[glass]] beads that looked to be [[tektite]]s.<ref>Hildebrand, Penfield, et al.</ref> Thick, jumbled deposits of coarse rock fragments were also present, thought to have been scoured from one place and deposited elsewhere by a [[megatsunami]] resulting from an Earth impact.<ref name=alanhild2/> Such deposits occur in many locations but seem concentrated in the [[Caribbean Basin|Caribbean]] basin at the K–Pg boundary.<ref name=alanhild2>Hildebrand interview: 'Similar deposits of rubble occur all across the southern coast of North America [...] indicate that something extraordinary happened here.'</ref> So when Haitian professor Florentine Morás discovered what he thought to be evidence of an ancient volcano on [[Haiti]], Hildebrand suggested it could be a telltale feature of a nearby impact.<ref name=moras>Morás.</ref> Tests on samples retrieved from the K–Pg boundary revealed more tektite glass, formed only in the heat of asteroid impacts and high-yield [[nuclear weapon|nuclear detonations]].<ref name=moras />
In 1990, ''[[Houston Chronicle]]'' reporter Carlos Byars told Hildebrand of Penfield's earlier discovery of a possible impact crater.<ref name=Frankel>Frankel, 50.</ref> Hildebrand contacted Penfield in April 1990 and the pair soon secured two drill samples from the Pemex wells, stored in [[New Orleans]].<ref name=alanhild>Hildebrand interview.</ref> Hildebrand's team tested the samples, which clearly showed [[Shock metamorphism|shock-metamorphic]] materials.
A team of California researchers including [[Kevin O. Pope|Kevin Pope]], [[Adriana Ocampo]], and Charles Duller, surveying regional satellite images in 1996, found a [[cenote]] ([[sinkhole]]) ring centered on Chicxulub that matched the one Penfield saw earlier; the sinkholes were thought to be caused by [[subsidence]] of the impact crater wall.<ref>Pope, Baines, et al.</ref> More recent evidence suggests the actual crater is {{convert|300|km|abbr=on}} wide, and the 180 km ring is in fact an inner wall of it.<ref>Sharpton & Marin.</ref>
==Impact specifics==
[[Image:Chicxulub-animation.gif|thumb|right|An animation showing the impact, and subsequent crater formation (University of Arizona, Space Imagery Center).]]
Researchers at the [[University of Glasgow]] dated tektites samples from the impact as 66,038,000 ± 11,000 years old.<ref>{{cite web|url=http://www.bbc.co.uk/news/uk-scotland-glasgow-west-21379024|title=Dinosaur extinction: Scientists estimate 'most accurate' date|work=BBC News}}</ref>
The [[Chicxulub impactor]] had an estimated diameter of 15km-wide (9.3 mi) <ref>http://www.bbc.com/news/science-environment-39922998</ref>, and delivered an estimated energy of 10 billion Hiroshima A-bombs (about 1E23 Joules, or 100,000 EJ) <ref>http://www.bbc.com/news/science-environment-39922998</ref> By contrast, the most powerful man-made explosive device ever detonated, the [[Tsar Bomba]], had an energy of only 210 [[peta-|peta]][[joule]]s (2.10E17 joules, the yield of 50 [[TNT equivalent#Kiloton and megaton|megaton]]s of TNT),<ref>Adamsky and Smirnov, 19.</ref>
===Effects===
[[Image:US map-Gulf Coast.svg|thumb|Some [[Gulf Coast of the United States|US states]] most affected by the Chicxulub megatsunami, though the coastline was different 66 million years ago]]
The impact would have caused a [[megatsunami]] over {{convert|100|m}} tall<ref name="Bryant">{{cite book |url=https://books.google.si/books?id=tOkpBAAAQBAJ&pg=PA178&lpg=PA17 |title=Tsunami: The Underrated Hazard |first=Edward |last=Bryant |date=June 2014 |publisher=Springer |isbn=9783319061337 |page=178}}</ref> that would have reached all the way to what are now Texas and Florida.<ref name="smithsonian1">{{cite web | url=http://www.smithsonianmag.com/science-nature/we-finally-know-how-much-dino-killing-asteroid-reshaped-earth-180958222/ | title=We Finally Know How Much the Dino-Killing Asteroid Reshaped Earth | publisher=[[Smithsonian Institution]] | date=February 25, 2016 | accessdate=February 26, 2016 | author=Palmer, Jane | website=Smithsonian.com}}</ref> The height of the tsunami was limited by the relatively shallow sea in the area of the impact; in deep sea it would have been {{convert|4.6|km}} tall.<ref name=Bryant /> A cloud of super-heated dust, ash and steam would have spread from the crater as the impactor burrowed underground in less than a second.<ref>Melosh, interview.</ref> Excavated material along with pieces of the impactor, ejected out of the atmosphere by the blast, would have been heated to [[incandescence]] upon re-entry, broiling the Earth's surface and possibly igniting wildfires; meanwhile, colossal [[shock wave]]s would have triggered global [[earthquakes]] and [[volcanic eruption]]s.<ref name=Molosh>Melosh. "On the ground, you would feel an effect similar to an oven on broil, lasting for about an hour [...] causing global forest fires."</ref>
The emission of dust and particles could have covered the entire surface of the Earth for several years, possibly a decade, creating a harsh environment for living things. The shock production of [[carbon dioxide]] caused by the destruction of [[carbonate]] rocks would have led to a sudden [[greenhouse effect]].<ref name=ppg5>Hildebrand, Penfield, ''et al.''; 5.</ref> Over a longer period, sunlight would have been blocked from reaching the surface of the Earth by the dust particles in the atmosphere, cooling the surface dramatically. [[Photosynthesis]] by plants would also have been interrupted, affecting the entire [[food chain]].<ref name=perlman>Perlman.</ref><ref name=popeandocampo>Pope, Ocampo, ''et al.''</ref> A model of the event developed by Lomax et al. (2001) suggests that [[Primary productivity#GPP and NPP|net primary productivity]] (NPP) rates may have increased to higher than pre-impact levels over the long term because of the high carbon dioxide concentrations.<ref name="Lomax">{{cite journal|last=Lomax|first=B.|author2=Beerling D.|authorlink2 = David Beerling|author3=Upchurch Jr. G.|author4=Otto-Bliesner B.|date=2001|title=Rapid (10-yr) recovery of terrestrial productivity in a simulation study of the terminal Cretaceous impact event|journal=Earth and Planetary Science Letters|volume=192|issue=2|pages=137–144|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V61-4441439-3&_user=10&_coverDate=10%2F15%2F2001&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1327486115&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=1f071c79677e3cb01503970a31509a1d|accessdate=May 8, 2010|doi=10.1016/S0012-821X(01)00447-2|bibcode=2001E&PSL.192..137L}}</ref>
In February 2008, a team of researchers led by Sean Gulick at the [[University of Texas at Austin]]'s [[Jackson School of Geosciences]] used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere. According to the press release, that "could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating [[acid rain]] (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain)."<ref>{{Cite news |url=http://www.jsg.utexas.edu/news/2008/01/seismic-images-show-dinosaur-killing-meteor-made-bigger-splash/ |title=Seismic Images Show Dinosaur-Killing Meteor Made Bigger Splash |date=January 1, 2008 |author=Marc Airhart}}</ref>
A long-term local effect of the impact was the creation of the Yucatán sedimentary basin which "ultimately produced favorable conditions for human settlement in a region where surface water is scarce."<ref>{{citation |url=http://www.asprs.org/a/publications/proceedings/tampa2007/0080.pdf|title=The Chicxulub Meteor Impact and Ancient Locational Decisions On the Yucatán Peninsula, Mexico: the Application of Remote Sensing, GIS, and GPS in Settlement Pattern Studies|last=Winemiller|first=Terance L.|publisher=[[American Society for Photogrammetry and Remote Sensing]]|place=Tampa, Florida|date=2007|accessdate=October 2, 2012}}</ref>
===Geology and morphology===
[[Image:Iridium clay layer.png|thumb|right|The piece of clay, held by Walter Alvarez, that sparked research into the impact theory. The greenish-brown band in the center is extremely rich in [[iridium]].]]
In their 1991 paper, Hildebrand, Penfield, and company described the geology and composition of the impact feature.<ref>Hildebrand, Penfield, ''et al.''; 1.</ref> The rocks above the impact feature are layers of [[marl]] and [[limestone]] reaching to a depth of almost {{convert|1000|m|ft|abbr=on}}. These rocks date back as far as the [[Paleocene]].<ref name=ppg3>Hildebrand, Penfield, ''et al.''; 3.</ref> Below these layers lie more than {{convert|500|m|ft|abbr=on}} of [[andesite]] glass and [[breccia]]. These andesitic [[igneous rock]]s were only found within the supposed impact feature, as is [[shocked quartz]].<ref name=ppg3/> The K–Pg boundary inside the feature is depressed to {{convert|600|to|1100|m|ft|abbr=on}} compared with the normal depth of about {{convert|500|m|ft|abbr=on}} measured {{convert|5|km|mi|abbr=on|0}} away from the impact feature.<ref name=ppg4>Hildebrand, Penfield, ''et al.''; 4.</ref> Along the edge of the crater are clusters of [[cenote]]s or sinkholes,<ref>{{cite web |url=https://www.youtube.com/watch?v=dNRTtLLuNM8 |title=Meteor Impact Site – Earth: The biography |publisher=National Geographic |date=July 11, 2008 |accessdate=August 19, 2015}}</ref> which suggest that there was a water basin inside the feature during the [[Neogene]] period, after the impact.<ref name=ppg4/> The [[groundwater]] of such a basin would have dissolved the [[limestone]] and created the caves and cenotes beneath the surface.<ref>Kring, "Discovering the Crater".</ref> The paper also noted that the crater seemed to be a good candidate source for the [[tektite]]s reported at [[Haiti]].<ref>Sigurdsson.</ref>
===Astronomical origin of asteroid===
In September 2007, a report published in ''[[Nature (journal)|Nature]]'' proposed an origin for the asteroid that created the Chicxulub Crater.<ref name=perlman/> The authors, [[William F. Bottke]], David Vokrouhlický, and [[David Nesvorný]], argued that a collision in the asteroid belt 160 million years ago resulted in the [[Baptistina family]] of asteroids, the largest surviving member of which is [[298 Baptistina]]. They proposed that the "Chicxulub asteroid" was also a member of this group. The connection between Chicxulub and Baptistina is supported by the large amount of carbonaceous material present in microscopic fragments of the impactor, suggesting the impactor was a member of a rare class of asteroids called [[carbonaceous chondrite]]s, like Baptistina.<ref name=Bottke/> According to Bottke, the Chicxulub impactor was a fragment of a much larger parent body about {{convert|170|km|abbr=on|0}} across, with the other impacting body being around {{convert|60|km|abbr=on}} in diameter.<ref name=Bottke>Bottke, Vokrouhlicky, Nesvorny.</ref><ref>Ingham.</ref> In 2011, new data from the [[Wide-field Infrared Survey Explorer]] revised the date of the collision which created the [[Baptistina family]] to about 80 million years ago. This makes an asteroid from this family highly improbable to be the asteroid that created the Chicxulub Crater, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.<ref name="Universe Today">{{cite news | first=Tammy | last=Plotner | title=Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... | url=http://www.universetoday.com/89050/did-asteroid-baptistina-kill-the-dinosaurs-think-other-wise/#more-89050 | work=Universe Today | date=2011| accessdate=September 19, 2011}}</ref> In 2010, another hypothesis was offered which implicated the newly discovered asteroid [[P/2010 A2]], a member of the [[Flora family]] of asteroids, as a possible remnant cohort of the K/Pg impactor.<ref>{{cite web|url=https://www.reuters.com/article/2010/02/02/us-space-asteroid-idUSTRE61154120100202|title=Smashed asteroids may be related to dinosaur killer|author=Reuters Editorial|date=February 2, 2010|work=Reuters}}</ref>
The Chicxulub Crater lends support to the theory postulated by the late [[physicist]] [[Luis Walter Alvarez|Luis Alvarez]] and his son, [[geologist]] [[Walter Alvarez]], that the extinction of numerous animal and plant groups, including non-avian [[dinosaur]]s, may have resulted from a [[bolide]] impact (the [[Cretaceous–Paleogene extinction event]]). Luis and Walter Alvarez, at the time both faculty members at the [[UC Berkeley|University of California, Berkeley]], postulated that this enormous extinction event, which was roughly contemporaneous with the postulated date of formation for the Chicxulub crater, could have been caused by just such a large impact.<ref>Alvarez, W. interview.</ref> The age of the rocks marked by the impact shows that this impact structure dates from roughly 66 million years ago, the end of the [[Cretaceous]] [[Period (geology)|period]], and the start of the [[Paleogene]] period. It coincides with the K–Pg boundary, the geological boundary between the Cretaceous and Paleogene. The impact associated with the crater is thus implicated in the [[Cretaceous–Paleogene extinction event]], including the worldwide extinction of non-avian [[dinosaur]]s. This conclusion has been the source of controversy. In March 2010, 41 experts from many countries reviewed the available evidence: 20 years' worth of data spanning a variety of fields. They concluded that the impact at Chicxulub triggered the [[mass extinction]]s at the K–Pg boundary.<ref name="science">Schulte, et al., 2010</ref><ref>Rincon.</ref> In 2013 a study compared [[isotope]]s in [[impact glass]] from the Chicxulub impact with the same isotopes in ash from the boundary where the [[extinction event]] occurred in the [[fossil record]]; the study concluded that the impact glasses were dated at 66.038 ± 0.049 Ma, and the deposits immediately above the discontinuity in the geological and fossil record was dated to 66.019 ± 0.021 Ma, the two dates being within 19,000 years of each other, or almost exactly the same within experimental error.<ref name=":0">{{cite journal|last1=Renne|first1=Paul|url=https://eps.harvard.edu/files/eps/files/renne.kt_.science.2013.pdf|title=Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary|journal=Science|date=8 February 2013|volume=339|page=684}}</ref> The theory is now widely accepted by the [[scientific community]]. Some critics, including [[paleontology|paleontologist]] [[Robert Bakker]], argue that such an impact would have killed [[frog]]s as well as dinosaurs, yet the frogs survived the extinction event.<ref>Kring, "Environment Consequences".</ref> [[Gerta Keller]] of [[Princeton University]] argues that recent core samples from Chicxulub prove the impact occurred about 300,000 years ''before'' the mass extinction, and thus could not have been the causal factor.<ref>Keller, ''et al.''</ref> However, this conclusion is unsupported by radioactive dating and sedimentology.<ref name="science" /><ref name=":0" />
The main evidence of such an impact, besides the crater itself, is contained in a thin layer of clay present in the [[Cretaceous–Paleogene boundary|K–Pg boundary]] across the world. In the late 1970s, the Alvarezes and colleagues reported that it contained an abnormally high concentration of [[iridium]].<ref name=alvarez>Alvarez.</ref> Iridium levels in this layer reached 6 parts per billion by weight or more compared to 0.4 for the Earth's crust as a whole;<ref>Web Elements.</ref> in comparison, meteorites can contain around 470 parts per billion of this element.<ref>Quivx.</ref> It was hypothesized that the iridium was spread into the atmosphere when the impactor was vaporized and settled across the Earth's surface amongst other material thrown up by the impact, producing the layer of iridium-enriched clay.<ref>Mayell.</ref> Similarly, an [[iridium anomaly]] in core samples from the [[Pacific Ocean]] suggested the [[Eltanin impact]] of about 2.5 million years ago.<ref name="Kyte1981">{{cite journal|last=Kyte|first=Frank T.|author2=Zhiming Zhou |author3=John T. Wasson |date=1981|title=High noble metal concentrations in a late Pliocene sediment|journal=Nature|volume=292|issue=5822|pages=417–420|issn=0028-0836|doi=10.1038/292417a0|bibcode = 1981Natur.292..417K }}</ref><ref name="Gersonde2">{{cite web|url=http://www.cosis.net/abstracts/EGU05/02449/EGU05-J-02449.pdf|title=The late Pliocene impact of the Eltanin asteroid into the Southern Ocean – Documentation and environmental consequences |last=Gersonde|first=R. |author2=F. T. Kyte |author3=T. Frederichs |author4=U. Bleil |author5=H. W. Schenke |author6=G. Kuhn |date=2005|work=Geophysical Research Abstracts|publisher=European Geosciences Union|accessdate=8 October 2012}}</ref>
==Multiple impact hypothesis==
In recent years, several other craters of around the same age as Chicxulub have been discovered, all between latitudes 20°N and 70°N. Examples include the disputed<ref>{{cite web|url=http://www.geolsoc.org.uk/Geoscientist/Archive/December-2009/Silverpit-not-crater#|title=Silverpit "not crater"|last=Riddle|first=Dawne|date=December 2009|publisher=[[Geological Society of London]]|accessdate=April 10, 2013}}</ref> [[Silverpit crater]] in the [[North Sea]]<ref>Stewart, Allen.</ref> and the [[Boltysh crater]] in [[Ukraine]].<ref>Kelley, Gurov.</ref> Both are much smaller than Chicxulub, but are likely to have been caused by objects many tens of meters across striking the Earth.<ref>Stewart.</ref> This has led to the hypothesis that the Chicxulub impact may have been only one of several impacts that happened nearly at the same time.<ref name=multiple/> Another possible crater thought to have been formed at the same time is the larger [[Shiva crater]],<ref name=Economist1009>{{cite news|url=http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=14698363|title=Mass extinctions: I am become Death, destroyer of worlds|date=October 22, 2009|publisher=The Economist|accessdate=October 24, 2009}}</ref> though the structure's status as a crater is contested.<ref>Mullen, "Shiva".</ref>
The collision of [[Comet Shoemaker–Levy 9]] with Jupiter in 1994 demonstrated that gravitational interactions can fragment a comet, giving rise to many impacts over a period of a few days if the comet should collide with a planet. Comets undergo gravitational interactions with the [[gas giant]]s, and similar disruptions and collisions are very likely to have occurred in the past.<ref name=Economist1009/><ref name=Weisstein>Weisstein.</ref> This scenario may have occurred on Earth at the end of the Cretaceous,<ref name=multiple>Mullen, "Multiple Impacts".</ref> though Shiva and the Chicxulub craters might have been formed 300,000 years apart.<ref name=Economist1009/>
In late 2006, Ken MacLeod, a [[geology]] professor from the [[University of Missouri]], completed an analysis of [[sediment]] below the ocean's surface, bolstering the single-impact theory. MacLeod conducted his analysis approximately {{convert|4,500|km}} from the Chicxulub Crater to control for possible changes in soil composition at the impact site, while still close enough to be affected by the impact. The analysis revealed there was only one layer of impact debris in the sediment, which indicated there was only one impact.<ref>Than.</ref> Multiple-impact proponents such as [[Gerta Keller]] regard the results as "rather hyper-inflated" and do not agree with the conclusion of MacLeod's analysis,<ref>Dunham.</ref> arguing that there might only be gaps of hours to days between impacts in a multiple-impact scenario (cf. Shoemaker-Levy 9) which would not leave a detectable gap in deposits.
==Scientific studies==
Chicxulub is the only known Earth crater with a remaining impact [[Peak ring (crater)|peak ring]], but it is under {{convert|600|m|abbr=on}} of sediment.<ref name="Régules 2015">{{cite journal |title=Revisiting the crater of doom |journal=Physics World Magazine |volume=28 |issue=9 |pages=33 |date=September 2015 |last=de Régules |first=Sergio|bibcode=2015PhyW...28i..33D |doi=10.1088/2058-7058/28/9/35 }}</ref> During April and May 2016, a joint [[IODP]]-[[International Continental Scientific Drilling Program|ICDP]]<ref>{{cite web|url=http://www.eso.ecord.org/expeditions/364/364.php/|title=ESO – Chicxulub K-Pg Impact Crater Expedition 364|publisher=}}</ref><ref>{{cite web|url=http://www.icdp-online.org/home/|title=ICDP Homepage|publisher=}}</ref> Mission Specific Platform Expedition obtained the first offshore [[core sample]]s from the peak ring, the central zone of the crater.<ref name="May 2016"/> During Expedition 364, DES<ref>{{cite web|url=http://dosecc.com/|title=DOSECC High Quality Core Drilling & Exploration Services|publisher=}}</ref> drillers on the ''L/B Myrtle''<ref>{{cite web|url=http://www.montco.com/MO/liftboat-myrtle-245-class.php|title=Liftboat Myrtle – Self-Elevating Vessel – Offshore Liftboat Services – Montco Offshore Liftboats|publisher=}}</ref> collected core samples to enable [[ECORD]]<ref>{{cite web|url=http://www.eso.ecord.org/expeditions/364/364.php|title=ESO – Chicxulub K-Pg Impact Crater Expedition 364|publisher=}}</ref> Science Party members to study how the peak ring formed and calculate the total impact energy.
Their target depth was {{convert|1500|m|abbr=on}} below the bottom of the ocean,<ref>{{cite news |last=Amos |first=Jonathan |url=http://www.bbc.com/news/science-environment-35950946 |title=Project to drill into 'dinosaur crater' gets under way |work=BBC News |date=5 April 2016 |accessdate=2016-04-05 }}</ref> but they reached an acceptable 1,335 m.<ref name="May 2016">{{cite news |last=Amos |first=Jonathan |url=http://www.bbc.com/news/science-environment-36377679 |title=Chicxulub 'dinosaur' crater drill project declared a success |work=BBC News |date=25 May 2016 |accessdate=2016-05-25 }}</ref> Sample preparation and analysis are being performed at Bremen, Germany.<ref name="Régules 2015"/>
It was announced in November 2016 that pink [[granite]], usually found deep in the Earth's crust had been found in drilling samples. It suggests the impact was so great it shocked rocks deep in the crust, causing them to shoot up before falling back down to produce the peak rings. The granite samples were also found to be lighter and weaker than normal granite.<ref>{{cite web|last1=St. Fleur|first1=Nicholas|title=Drilling Into the Chicxulub Crater, Ground Zero of the Dinosaur Extinction|url=https://www.nytimes.com/2016/11/18/science/chicxulub-crater-dinosaur-extinction.html?_r=0|website=The New York Times|accessdate=19 November 2016}}</ref>
A program on British television<ref>''The Day the Dinosaurs Died'', [[BBC2]] television, 1 July 2017, 6 to 7 pm</ref> described:
* A deep drilling into the inner ring of the Chicxulub crater. It found, from top down:
** Thick Cenozoic limestone.
** A graded sediment deposit from one [[tsunami]], over 100 meters thick.
** Impact-melted rock and [[shocked quartz]]. This did not contain the [[calcium sulphate]] that the rocks in the area around contain, leading the program makers to conclude that all the calcium sulphate in the crater area had been evaporated into the atmosphere and had become a dense [[sulphur dioxide]] veil stopping the sunlight.
* In a quarry in New Jersey, a dense marine [[bone bed]] on the Cretaceous-Tertiary boundary containing a mixture of dead sea animals with little or no damage from scavengers or predators, and land animals and parts of trees washed into the sea by a tsunami.
* In [[Patagonia]] a dense dinosaur bone bed on the Cretaceous-Tertiary boundary.
==See also==
* [[Timeline of Cretaceous-Paleogene extinction event research]]
*[[Deccan Traps]]
*[[List of impact craters on Earth]]
*[[List of unconfirmed impact craters on Earth]] – craters similar to or larger than Chicxulub
*[[Permian–Triassic extinction event]]
==Notes==
{{Reflist|30em}}
==References==
{{Refbegin|30em}}
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{{Refend}}
==Further reading==
* {{Cite journal |last=Schulte |first=P. |last2=Alegret |first2=L. |last3=Arenillas |first3=I. |last4=Arz |first4=J. A. |last5=Barton |first5=P. J. |last6=Bown |first6=P. R. |last7=Bralower |first7=T. J. |last8=Christeson |first8=G. L. |last9=Claeys |first9=P. |displayauthors=3 |year=2010 |title=The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary |url=http://www3.nd.edu/~cneal/CRN_Papers/Schulte10_Sci_Chicxulub.pdf |journal=Science |volume=327 |issue=5970 |pages=1214–1218 |doi=10.1126/science.1177265 |issn=0036-8075 |archive-url=https://web.archive.org/web/20111209132114/http://www.nd.edu/~cneal/CRN_Papers/Schulte10_Sci_Chicxulub.pdf |archive-date=December 9, 2011 |access-date=9 December 2016 |last10=Cockell |first10=C. S. |last11=Collins |first11=G. S. |last12=Deutsch |first12=A. |last13=Goldin |first13=T. J. |last14=Goto |first14=K. |last15=Grajales-Nishimura |first15=J. M. |last16=Grieve |first16=R. A. F. |last17=Gulick |first17=S. P. S. |last18=Johnson |first18=K. R. |last19=Kiessling |first19=W. |last20=Koeberl |first20=C. |last21=Kring |first21=D. A. |last22=MacLeod |first22=K. G. |last23=Matsui |first23=T. |last24=Melosh |first24=J. |last25=Montanari |first25=A. |last26=Morgan |first26=J. V. |last27=Neal |first27=C. R. |last28=Nichols |first28=D. J. |last29=Norris |first29=R. D. |last30=Pierazzo |first30=E. |last31=Ravizza |first31=G. |last32=Rebolledo-Vieyra |first32=M. |last33=Reimold |first33=W. U. |last34=Robin |first34=E. |last35=Salge |first35=T. |last36=Speijer |first36=R. P. |last37=Sweet |first37=A. R. |last38=Urrutia-Fucugauchi |first38=J. |last39=Vajda |first39=V. |last40=Whalen |first40=M. T. |last41=Willumsen |first41=P. S. |pmid=20203042}}
* [http://bbs.keyhole.com/ubb/download.php?Number=1226046 Numerous sinkholes (Cenotes) marked around Chicxulub crater.] Opens in Google Earth
* [http://www.jpl.nasa.gov/news/features.cfm?feature=8 NASA JPL: "A 'Smoking Gun' for Dinosaur Extinction"], March 6, 2003
* [http://www.lpi.usra.edu/publications/slidesets/craters/slide_37.html Chicxulub: Variations in the magnitude of the gravity field at sea level image] (Lunar and Planetary Institute, USRA)
* [http://www.scientificamerican.com/article.cfm?id=doubts-on-dinosaurs "Doubts On Dinosaurs"]—''[[Scientific American]]''
{{KT_boundary|K–Pg boundary}}
{{Impact cratering on Earth}}
{{DEFAULTSORT:Chicxulub Crater}}
[[Category:Cretaceous impact craters]]
[[Category:Dinosaurs]]
[[Category:Extinction events]]
[[Category:Geological history of Earth]]
[[Category:Impact craters of Mexico]]
[[Category:Mérida, Yucatán]]
[[Category:Natural history of the Caribbean]]
[[Category:Natural history of the Yucatán Peninsula]]
