For the Permian-Triassic extinction event, see: P-T extinction
Impact event

Artist's conception of an asteroid impact comparable to the Alvarez hypothesis of the Chicxulub crater impact theory.

The Cretaceous–Paleogene (K–Pg) extinction event,[fn 1] also known as the Cretaceous–Tertiary (K–T) extinction,[fn 2] was a mass extinction of some three-quarters of the plant and animal species on Earth that occurred over a geologically short period of time,[2][3][4] approximately 66 million years ago.[3] With the exception of some ectothermic species such as the leatherback sea turtle and crocodiles, no tetrapods weighing more than 25 kilograms (55 lb) survived.[5] It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth's crust, but abundant in asteroids.[6]

As originally proposed in 1980 by a team of scientists led by Luis Alvarez and Walter Alvarez, it is now generally thought that the K–Pg extinction was caused by a massive comet or asteroid impact, estimated to be Template:Convert/km to Template:Convert/km wide,[7][8] 66 million years ago[3] and its catastrophic effects on the global environment, including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis.[9][10]

The K-T Extinction Event marked the end of the Mesozoic Era, the "Age of Reptiles" and began the Cenozoic Era, the "Age of Mammals".

See alsoEdit


  1. The abbreviation is derived from the juxtaposition of K, the common abbreviation for the Cretaceous, which in turn originates from the correspondent German term Kreide, and Pg, which is the abbreviation for the Paleogene.
  2. The former designation includes the term 'Tertiary' (abbreviated as T), which is now discouraged as a formal geochronological unit by the International Commission on Stratigraphy.[1]


  1. Ogg, James G.; Gradstein, F. M; Gradstein, Felix M. (2004). A geologic time scale 2004. Cambridge, UK: Cambridge University Press. ISBN 0-521-78142-6. 
  2. "International Chronostratigraphic Chart". International Commission on Stratigraphy. 2015. Retrieved on 29 April 2015. 
  3. 3.0 3.1 3.2 Renne, Paul R.; Deino, Alan L.; Hilgen, Frederik J.; Kuiper, Klaudia F.; Mark, Darren F.; Mitchell, William S.; Morgan, Leah E.; Mundil, Roland; et al. (7 February 2013). "Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary". Science 339 (6120): 684–687. doi:10.1126/science.1230492. PMID 23393261. Bibcode2013Sci...339..684R. 
  4. Fortey, Richard (1999). Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage. pp. 238–260. ISBN 978-0-375-70261-7. 
  5. Muench, David; Muench, Marc; Gilders, Michelle A. (2000). Primal Forces. Portland: Graphic Arts Center Publishing. pp. 20. ISBN 1-55868-522-7. 
  6. Schulte, Peter (March 5, 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary". Science (American Association for the Advancement of Science) 327 (5970): 1214–1218. doi:10.1126/science.1177265. PMID 20203042. Bibcode2010Sci...327.1214S. 
  7. Sleep, Norman H.; Lowe, Donald R. (9 April 2014). "Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast". American Geophysical Union. Retrieved on 30 December 2016. 
  9. "Extraterrestrial cause for the Cretaceous–Tertiary extinction". Science 208 (4448): 1095–1108. 1980. doi:10.1126/science.208.4448.1095. PMID 17783054. Bibcode1980Sci...208.1095A. 
  10. Vellekoop, J.; Sluijs, A.; Smit, J.; Schouten, S.; Weijers, J. W. H.; Sinninghe Damste, J. S.; Brinkhuis, H. (May 2014). "Rapid short-term cooling following the Chicxulub impact at the Cretaceous-Paleogene boundary". Proc. Natl. Acad. Sci. U.S.A. 111 (21): 7537–41. doi:10.1073/pnas.1319253111. PMID 24821785. Bibcode2014PNAS..111.7537V.