DOI: 10.1126/science.1177265 , 1214 (2010); 327Science et al.Peter Schulte,at the Cretaceous-Paleogene BoundaryThe Chicxulub Asteroid Impact and Mass ExtinctionThis copy is for your personal, non-commercial use only.. clicking herecolleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others. herefollowing the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles (this information is current as of September 14, 2010 ):The following resources related to this article are available online at www.sciencemag.org http://www.sciencemag.org/cgi/content/full/327/5970/1214version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/327/5970/1214/DC1 can be found at: Supporting Online Materialfound at: can berelated to this articleA list of selected additional articles on the Science Web sites http://www.sciencemag.org/cgi/content/full/327/5970/1214#related-content http://www.sciencemag.org/cgi/content/full/327/5970/1214#otherarticles, 17 of which can be accessed for free: cites 54 articlesThis article http://www.sciencemag.org/cgi/collection/geochem_physGeochemistry, Geophysics : subject collectionsThis article appears in the following registered trademark of AAAS. is aScience2010 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on September 14, 2010 www.sciencemag.orgDownloaded fromThe Chicxulub Asteroid Impactand Mass Extinction at theCretaceous-Paleogene BoundaryPeter Schulte,1* Laia Alegret,2Ignacio Arenillas,2José A. Arz,2Penny J. Barton,3Paul R. Bown,4TimothyJ.Bralower,5Gail L. Christeson,6Philippe Claeys,7Charles S. Cockell,8Gareth S. Collins,9Alexander Deutsch,10Tamara J. Goldin,11Kazuhisa Goto,12José M. Grajales-Nishimura,13Richard A. F. Grieve,14Sean P. S. Gulick,6Kirk R. Johnson,15Wolfgang Kiessling,16Christian Koeberl,11David A. Kring,17Kenneth G. MacLeod,18Takafumi Matsui,19Jay Melosh,20Alessandro Montanari,21Joanna V. Morgan,9Clive R. Neal,22Douglas J. Nichols,15Richard D. Norris,23Elisabetta Pierazzo,24Greg Ravizza,25Mario Rebolledo-Vieyra,26Wolf Uwe Reimold,16Eric Robin,27Tobias Salge,28Robert P. Speijer,29Arthur R. Sweet,30Jaime Urrutia-Fucugauchi,31Vivi Vajda,32Michael T. Whalen,33Pi S. Willumsen32The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest massextinctions in the past 500 million years. The extinction event coincided with a large asteroidimpact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism inIndia. Here, we synthesize records of the global stratigraphy across this boundary to assess theproposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linkedto the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. Thetemporal match between the ejecta layer and the onset of the extinctions and the agreement ofecological patterns in the fossil record with modeled environmental perturbations (for example,darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.Paleontologists have long recognized theglobal scale and abruptness of the majorbiotic turnov er at the Cretaceous- Paleogene(K-Pg, formerly K-T) boundary ~ 65.5 millionyears ago (Ma). This boundary represents one ofthe most devastating events in the history of life(1) and abruptly ended the age of the dinosaurs.Thirty years ago, the discovery of an anomalouslyhigh abundance of iridium and other platinumgroup e lements (PGEs) in the K-Pg boundaryclay led to the hypothesis that an asteroid ~10 kmin diameter collided with Earth and rendered manyenvironments uninhabitable (2, 3).The occurrence of an impact is substantiatedby the recognition of impact ejecta includingspherules, shocked minerals, and Ni-rich spinelsin many K-Pg boundary event deposits [e.g.,(4, 5)]. The ejecta distribution points to an impactevent in the Gulf of Mexico–Caribbean region;this prediction is reinforced by the discovery ofthe ~180- to 200-km-diameter Chicxulub craterstructure on the Yucatan peninsula, Mexico (6).Modeling suggests that the size of the crater andthe release of climatically sensitive gases fromthe carbonate- and sulfate-rich target rocks couldhave caused catastrophic environmental effectssuch as extended darkness, global cooling, andacid rain (7–9). These effects provide an arrayof potential mechanisms for the ecologicallydiverse but selective abrupt extinctions (Fig. 1)(10–13).Notwithstanding the substantial evidence sup-porting an impact mechanism, other interpre-tations of the K-Pg boundary mass extinctionremain. Stratigraphic and micropaleontologicaldata from the Gulf of Mexico and the Chicxulubcrater have instead been used to argue that thisimpact preceded the K-Pg boundary by severalhundred thousand years and therefore could nothave caused the mass extinction [e.g., (14)]. Inaddition, the approximately one-million-year-longemplacement of the large Deccan flood basaltsin India spans the K-Pg boundary (Fig. 1); therelease of sulfur and carbon dioxide during thesevoluminous eruptions may have caused severeenvironmental effects (15) that have also beenproposed as triggers for the mass extinction atthe K-Pg boundary (16).Here, we assess the observational support forthese divergent interpretations by synthesizingrecent stratigraphic, micropaleontological, petro-logical, and geochemical data from the globallydistributed K-Pg boundary event deposit. Impactand volcanism as extinction mechanisms areevaluated in terms of their predicted environ-mental perturbations and, ultimately, the dis-tributionoflifeonEarthbeforeandaftertheK-Pg boundary .What Is the Evidence for Correlating the Impactwith the K-Pg Boundary?The Upper Cretaceous and lower Paleogenesediments bracketing the K-Pg boundary eventdeposits are among the most intensively in-vestigated deposits in the geological record.More than 350 K-Pg boundary sites are cur-rently known, and these sites show a distinctejecta distribution pattern related to distancefrom the Chicxulub crater (Fig. 2 and