Editing 1991 in science (section)

==Geophysics==
* [[Alan Hildebrand]] and others provide support for the [[Alvarez hypothesis]] for the [[Cretaceous–Paleogene extinction event]] by proposing the [[Chicxulub crater]] in the [[Yucatán Peninsula]] of [[Mexico]] as the [[Impact crater|impact site]] for a large [[asteroid]] 66 million years ago.<ref>{{cite journal|author=Pope, Kevin O.|title=Mexican site for K/T impact crater?|journal=[[Nature (journal)|Nature]]|volume=351|date=9 May 1991|page=105|issue=6322|doi=10.1038/351105a0|bibcode = 1991Natur.351..105P |s2cid=36707836|display-authors=etal|doi-access=free}}</ref><ref>{{cite journal|author1=Hildebrand, Alan R. |author2=Penfield, Glen T. |author3=Kring, David A. |author4=Pilkington, Mark |author5=Zanoguera, Antonio Camargo |author6=Jacobsen, Stein B. |author7=Boynton, William V. |title=Chicxulub Crater: a possible Cretaceous/Tertiary Boundary impact crater on the Yucatán Peninsula, Mexico|date=September 1991|volume=19|issue=9|journal=[[Geology (journal)|Geology]]|pages=867–871|doi=10.1130/0091-7613(1991)019<0867:CCAPCT>2.3.CO;2|bibcode=1991Geo....19..867H}}</ref><ref>{{cite journal|author=Schulte, Peter|title=The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous- Paleogene Boundary|journal=[[Science (journal)|Science]]|volume=327|pages=1214–1218|year=2010|doi=10.1126/science.1177265|pmid=20203042|issue=5970|bibcode=2010Sci...327.1214S|s2cid=2659741|url=http://doc.rero.ch/record/210367/files/PAL_E4389.pdf|display-authors=etal}}</ref>
* The [[Ames crater]] [[impact structure]] is identified in [[Major County, Oklahoma]].