K-Pg extinction event

[[File:KT Impact2.jpg|thumb|right|165px|An artist's conception of the asteroid collision which probably caused the Cretaceous-Tertiary Extinction Event]]
{{Geology}}
The '''Cretaceous-Paleogene extinction event''' (aka the '''Cretaceous-Tertiary extinction event''', abbreviated as either the '''K-T extinction event''' or the '''K-Pg extinction event''') was a major [[mass extinction]] event that took place around 66 million years ago, and led to the deaths of a large number of organisms around the globe, including all of the [[dinosaur]]s (except [[birds]]). An estimated 76% of all the plants and animals species that existed at the time died out.<ref>[https://www.jstor.org/stable/56148 Extinctions in the Fossil Record] by David Jablonski & W. G. Chaloner (1994) ''Philosophical Transactions: Biological Sciences'' 344(1307):11-17.</ref>

==Causes of the extinction==
There may have ultimately been multiple different causes for the K-Pg extinction event, but what is widely agreed upon is that the major catalyst for the extinction was a 10–15 km [[asteroid]] or [[comet]] that hit what is now the Yucatán peninsula of [[Mexico]], and formed the {{wpl|Chicxulub crater||.}}<ref>Hildebrand, A. R.; Penfield, G. T.; et al. (1991). "Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatán peninsula, Mexico". ''Geology''. 19 (9): 867–871. doi:10.1130/0091-7613</ref> Other hypothesized causes have included the {{wpl|Deccan Traps}}<ref group=note>A period of flood basalt eruptions that were one of the largest eruptions in Earth's history</ref><ref>Petersen Sierra V., Dutton Andrea, Lohmann Kyger C. (2016). "End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change". ''Nature Communications''. 7: 12079. doi:10.1038/ncomms12079.</ref> Strangely enough, the extinction ratios of clades affected by the extinction suggests that the extinction was ultimately due to the re-entry of ejecta into the atmosphere after the impact occurred.<ref>[https://groups.google.com/forum/#!original/sci.bio.paleontology/7RpgzUW6O3M/LkXRBm3bAwAJ Non-mammals during the Earliest Paleocene]</ref>

===Alternate extinction hypotheses===
There is some residual debating regarding the exact causes of the K-Pg extinction event, with some people believing that the event was actually caused by something other than the asteroid impact. In general the evidence favors a combination of factors including the Deccan Traps and the impact, but the impact was definitely the main factor. While it has been debated whether or not dinosaurs experienced a decline prior to the terminal Cretaceous extinction event, a study published in the journal ''The Proceedings of the National Academy of Sciences'' conducted a thorough analysis for the first time and found that the data supports a long-term decline among non-avian dinosaurs prior to the aforementioned end-Cretaceous extinction event.<ref>[http://www.pnas.org/content/early/2016/04/13/1521478113 Dinosaurs in decline tens of millions of years before their final extinction]</ref>

==Extinction ratios==
Freshwater biomes were in general less affected by the K-Pg extinction event than their terrestrial or marine counterparts, with amphibians in particular not being generally affected by the extinction event, with only a few extinctions among them.<ref>Sheehan, P. M.; Fastovsky, D. E. (1992). "Major extinctions of land-dwelling vertebrates at the Cretaceous-Tertiary boundary, Eastern Montana". ''Geology''. 20 (6): 556–560. doi:10.1130/0091-7613</ref> Terrestrial organisms were hit hard, however, with the extinction of all birds outside of [[Neornithes]],<ref>Hou, L; Martin, M; Zhou, Z; Feduccia, A (1996). "Early Adaptive Radiation of Birds: Evidence from Fossils from Northeastern China". ''Science''. 274 (5290): 1164–1167. doi:10.1126/science.274.5290.1164. PMID 8895459.</ref> all [[pterosaur]]s, all non-avian dinosaurs, various groups of marine fish, and entire clades of [[mammals]] (marsupials used to be the dominant mammals in North America, but after the K-Pg extinction event only a few marsupials remained, among them ''Peradectes'', with the mammals above the K-Pg boundary layer that dominated North America being placentals). The oceans were hit hard as well, with almost every marine reptile outside of sea turtles going extinct, not to mention the extinction of the ammonites and the belemnites.<ref group=note>Just like in {{bible|2 Samuel|12|26}}</ref>

The nature of the victims of this extinction event notably make [[pseudoscientific]] [[cryptozoological]] claims all the more ridiculous. If {{wpl|Yuornis|sparrow-sized birds}} didn't make it, do you seriously think [[Mokele-mbembe|a sauropod]] would?

==See also==
*[[History of the Earth]]
*[[Palaeocene]] — the first epoch of the [[Paleogene]] period of the modern [[Cenozoic]] era
*[[Dinosaurs]] - The most notable taxon to be rendered extinct by this extinction event, excluding neornithine birds.

==Notes==
{{reflist|group=note}}

==References==
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[[Category:Geology]]
[[Category:Paleontology]]
[[Category:Evidence against a recent creation]]

Categories: Geology, Paleontology, Evidence against a recent creation