Editing Dinosaur (section)

===Impact event===
{{Main|Chicxulub crater}}
[[File:LWA with Walt.JPG|thumb|upright|[[Luis Walter Alvarez|Luis]] (left) and his son [[Walter Alvarez]] (right) at the K-T Boundary in [[Gubbio]], Italy, 1981]]
[[File:Chicxulub radar topography.jpg|thumb|The [[Chicxulub Crater]] at the tip of the [[Yucatán Peninsula]]; the impactor that formed this crater may have caused the dinosaur [[extinction]].]]
The [[Alvarez hypothesis|bolide impact hypothesis]], first brought to wide attention in 1980 by [[Walter Alvarez]], [[Luis Walter Alvarez|Luis Alvarez]], and colleagues, attributes the K-Pg extinction event to a [[bolide]] (extraterrestrial projectile) impact.<ref>{{harvnb|Randall|2015}}</ref> Alvarez and colleagues proposed that a sudden increase in [[iridium]] levels, recorded around the world in rock deposits at the Cretaceous–Paleogene boundary, was direct evidence of the impact.<ref name="alvarez1980"/> [[Shocked quartz]], indicative of a strong shockwave emanating from an impact, was also found worldwide.<ref name="bohor1987">{{cite journal |last1=Bohor |first1=B.F. |last2=Modreski |first2=P.J. |last3=Foord |first3=E.E. |year=1987 |title=Shocked quartz in the Cretaceous-Tertiary boundary clays: Evidence for a global distribution |journal=Science |volume=236 |issue=4802 |pages=705–709 |doi=10.1126/science.236.4802.705 |pmid=17748309 |bibcode=1987Sci...236..705B |s2cid=31383614 |url=https://zenodo.org/record/1230978 |archive-date=February 26, 2021 |access-date=February 8, 2021 |archive-url=https://web.archive.org/web/20210226190627/https://zenodo.org/record/1230978 |url-status=live }}</ref> The actual impact site remained elusive until a [[Chicxulub crater|crater]] measuring {{convert|180|km|mi|abbr=on}} wide was discovered in the Yucatán Peninsula of southeastern [[Mexico]], and was publicized in a 1991 paper by [[Alan R. Hildebrand|Alan Hildebrand]] and colleagues.<ref name="hildebrand1991">{{cite journal |last1=Hildebrand |first1=A.R. |last2=Penfield |first2=G.T. |last3=Kring |first3=D.A. |last4=Pilkington |first4=M. |last5=Camargo |first5=Z.A. |last6=Jacobsen |first6=S.B. |last7=Boynton |first7=W.V. |year=1991 |title=Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico |journal=Geology |volume=19 |issue=9 |pages=867–871 |doi=10.1130/0091-7613(1991)019<0867:CCAPCT>2.3.CO;2|bibcode=1991Geo....19..867H }}</ref> Now, the bulk of the evidence suggests that a bolide {{convert|5|to|15|km|mi|frac=2|abbr=off|sp=us}} wide impacted the Yucatán Peninsula 66 million years ago, forming this crater<ref name="pope1996"/> and creating a "kill mechanism" that triggered the extinction event.<ref name="schulte2010">{{cite journal |last1=Schulte |first1=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. |last10=Cockell |first10=C.S. |last11=Collins |first11=G.S. |first12=A. |last12=Deutsch |first13=T.J. |last13=Goldin |first14=K. |last14=Goto |first15=J.M. |last15=Grajales-Nishimura |first16=R.A.F. |last16=Grieve |first17=S.P.S. |last17=Gulick  |first18=K.R. |last18=Johnson |first19=W. |last19=Kiessling |first20=C. |last20=Koeberl |first21=D.A. |last21=Kring |first22=K.G. |last22=MacLeod |first23=T. |last23=Matsui |first24=J. |last24=Melosh |first25=A. |last25=Montanari |first26=J.V. |last26=Morgan |first27=C.R. |last27=Neal |first28=D.J. |last28=Nichols |first29=R.D. |last29=Norris |first30=E. |last30=Pierazzo |first31=G. |last31=Ravizza |first32=M. |last32=Rebolledo-Vieyra |first33=W. |last33=Uwe Reimold |first34=E. |last34=Robin |first35=T. |last35=Salge |first36=R.P. |last36=Speijer |first37=A.R. |last37=Sweet |first38=J. |last38=Urrutia-Fucugauchi |first39=V. |last39=Vajda |first40=M.T. |last40=Whalen |first41=P.S. |last41=Willumsen |year=2010 |title=The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary |journal=Science |volume=327 |issue=5970 |pages=1214–1218 |doi=10.1126/science.1177265|pmid=20203042 |bibcode=2010Sci...327.1214S |s2cid=2659741 |url=https://lirias.kuleuven.be/handle/123456789/264213 }}</ref><ref name="kring2007">{{cite journal |last1=Kring |first1=D. A. |year=2007 |title=The Chicxulub impact event and its environmental consequences at the Cretaceous–Tertiary boundary |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=255 |issue=1–2 |pages=4–21 |doi=10.1016/j.palaeo.2007.02.037|bibcode=2007PPP...255....4K }}</ref><ref name="chiarenza2020">{{cite journal |last1=Chiarenza |first1=A.A. |last2=Farnsworth |first2=A. |last3=Mannion |first3=P.D. |last4=Lunt |first4=D.J. |last5=Valdes |first5=P.J. |last6=Morgan |first6=J.V.|author6-link= Joanna Morgan |last7=Allison |first7=P.A. |year=2020 |title=Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=29 |pages=17084–17093 |doi=10.1073/pnas.2006087117|pmid=32601204 |pmc=7382232 |bibcode=2020PNAS..11717084C |doi-access=free }}</ref>

Within hours, the Chicxulub impact would have created immediate effects such as earthquakes,<ref name="ivanov2005">{{cite journal |last1=Ivanov |first1=B.A. |year=2005 |title=Numerical Modeling of the Largest Terrestrial Meteorite Craters |journal=Solar System Research |volume=39 |issue=5 |pages=381–409 |doi=10.1007/s11208-005-0051-0|bibcode=2005SoSyR..39..381I |s2cid=120305483 }}</ref> tsunamis,<ref name="matsui2002">{{cite journal |last1=Matsui |first1=T. |last2=Imamura |first2=F. |last3=Tajika |first3=E. |last4=Nakano |first4=Y. |last5=Fujisawa |first5=Y. |year=2002 |title=Generation and propagation of a tsunami from the Cretaceous-Tertiary impact event |journal=Geological Society of America Special Papers |volume=356 |pages=69–78 |doi=10.1130/0-8137-2356-6.69|isbn=978-0-8137-2356-3 }}</ref> and a global firestorm that likely killed unsheltered animals and started wildfires.<ref name="robertson2004">{{cite journal |last1=Robertson |first1=D.S. |last2=McKenna |first2=M.C. |author2-link=Malcolm McKenna |last3=Toon |first3=O.B. |author3-link=Owen Toon |last4=Hope |first4=S. |last5=Lillegraven |first5=J.A. |display-authors=3 |year=2004 |title=Survival in the first hours of the Cenozoic |url=http://webh01.ua.ac.be/funmorph/raoul/macroevolutie/Robertson2004.pdf |journal=[[Geological Society of America Bulletin]] |volume=116 |issue=5–6 |pages=760–768 |bibcode=2004GSAB..116..760R |doi=10.1130/B25402.1 |issn=0016-7606 |archive-url=https://web.archive.org/web/20120918141759/http://webh01.ua.ac.be/funmorph/raoul/macroevolutie/Robertson2004.pdf |archive-date=September 18, 2012 |access-date=June 15, 2011}}</ref><ref name="robertson2013">{{cite journal |last1=Robertson |first1=D.S. |last2=Lewis |first2=W.M. |last3=Sheehan |first3=P.M. |last4=Toon |first4=O.B. |year=2013 |title=K-Pg extinction: Reevaluation of the heat-fire hypothesis |journal=Journal of Geophysical Research: Biogeosciences |volume=118 |issue=1 |pages=329–336 |doi=10.1002/jgrg.20018|bibcode=2013JGRG..118..329R |s2cid=17015462 |doi-access=free }}</ref> However, it would also have had longer-term consequences for the environment. Within days, sulfate [[aerosol]]s released from rocks at the impact site would have contributed to [[acid rain]] and [[ocean acidification]].<ref name="pope1997">{{cite journal |last1=Pope |first1=K.O. |last2=Baines |first2=K.H. |last3=Ocampo |first3=A.C. |last4=Ivanov |first4=B.A. |year=1997 |title=Energy, volatile production, and climatic effects of the Chicxulub Cretaceous/Tertiary impact |journal=Journal of Geophysical Research: Planets |volume=102 |issue=E9 |pages=21645–21664 |doi=10.1029/97JE01743|pmid=11541145 |bibcode=1997JGR...10221645P |s2cid=8447773 |doi-access=free }}</ref><ref name="ohno2014"/> [[Soot]] aerosols are thought to have spread around the world over the ensuing months and years; they would have cooled the surface of the Earth by reflecting [[thermal radiation]], and greatly slowed [[photosynthesis]] by blocking out sunlight, thus creating an [[impact winter]].<ref name="brusatte2014"/><ref name="kaiho2016">{{cite journal |last1=Kaiho |first1=K. |last2=Oshima |first2=N. |last3=Adachi |first3=K. |last4=Adachi |first4=Y. |last5=Mizukami |first5=T. |last6=Fujibayashi |first6=M. |last7=Saito |first7=R. |year=2016 |title=Global climate change driven by soot at the K-Pg boundary as the cause of the mass extinction |journal=Scientific Reports |volume=6 |issue=1 |pages=1–13 |doi=10.1038/srep28427|pmid=27414998 |pmc=4944614 |bibcode=2016NatSR...628427K }}</ref><ref name="lyons2020">{{cite journal |last1=Lyons |first1=S.L. |last2=Karp |first2=A.T. |last3=Bralower |first3=T.J. |last4=Grice |first4=K. |last5=Schaefer |first5=B. |last6=Gulick |first6=S.P. |last7=Morgan |first7=J.V.|author7-link= Joanna Morgan |last8=Freeman |first8=K.H. |year=2020 |title=Organic matter from the Chicxulub crater exacerbated the K–Pg impact winter |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=41 |pages=25327–25334 |doi=10.1073/pnas.2004596117|pmid=32989138 |pmc=7568312 |bibcode=2020PNAS..11725327L |doi-access=free }}</ref> (This role was ascribed to [[sulfate]] aerosols until experiments demonstrated otherwise.<ref name="ohno2014">{{cite journal |last1=Ohno |first1=S. |last2=Kadono |first2=T. |last3=Kurosawa |first3=K. |last4=Hamura |first4=T. |last5=Sakaiya |first5=T. |last6=Shigemori |first6=K. |last7=Hironaka |first7=Y. |last8=Sano |first8=T. |last9=Watari |first9=T. |last10=Otani |first10=K. |last11=Matsui |first11=T. |last12=Sugita |first12=S. |year=2014 |title=Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification |journal=Nature Geoscience |volume=7 |issue=4 |pages=279–282 |doi=10.1038/ngeo2095|bibcode=2014NatGe...7..279O }}</ref>) The cessation of photosynthesis would have led to the collapse of [[food web]]s depending on leafy plants, which included all dinosaurs save for grain-eating birds.<ref name="larson2016"/>