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K/T extinction event

extinction event ending the Mesozoic Era
The intermediate claystone layer contains 1000 times more iridium than the upper and lower layers. It is the boundary between Cretaceous and Tertiary Periods. The rock is from Wyoming, USA.
This image of Mexico's Yucatán Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists agree that this impact was the main cause of the Cretaceous-Tertiary extinction.

The CretaceousTertiary extinction event, now called the Cretaceous–Palaeogene extinction event,[1] was about 66 million years ago.[2] It may be called the K/T extinction event or K/Pg event for short. This is the famous event which killed the dinosaurs at the end of the Cretaceous period.

It was a large-scale mass extinction of animal and plant species. The event marks the end of the Mesozoic era and the beginning of the Cenozoic era.[3][4]


Dinosaur fossils are only found below the K/T boundary. This shows they became extinct before, or during the event.[5] Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct.

Mammalian and bird groups got through the event with some extinctions. Those that survived became widespread and varied during their later evolutionary radiation.[6]


Scientists think the K/T extinctions were caused by something sudden and powerful, such as one or more massive asteroid or meteor impacts, and increased volcanic activity.

Scientists study what happened to the dinosaurs and other groups to learn what caused the K/T extinction event. How quickly they died out around the world is an important clue.[5]

Scientists also study patterns in rocks to learn the causes. Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, are dated to about the same time as the extinctions. Those impacts and volcanoes would have reduced sunlight and hindered photosynthesis, disrupting Earth's ecology.[6]


Evidence is accumulating that there were multiple impact events across the Cretaceous/Tertiary boundary, such as the Chicxulub crater in Mexico, Boltysh crater in Ukraine, Silverpit crater in North Sea, and the Shiva crater offshore western India.[7][8] The Shiva crater is a sea floor structure under the continental shelf in the Indian Ocean, west of Mumbai, India. It was named by paleontologist Sankar Chatterjee after Shiva, the Hindu god of destruction and renewal.

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  1. Because the term "Tertiary" is out of date.
  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. 
  3. Fortey R (1999). Life: A natural history of the first four billion years of life on Earth. Vintage. pp. 238–260.
  4. With "Tertiary" being discouraged as a formal time or rock unit by the International Commission on Stratigraphy, the K/T event is now called the Cretaceous–Palaeogene extinction event by many researchers. Gradstein F, Ogg J, Smith A. A geologic time scale 2004.CS1 maint: multiple names: authors list (link)
  5. 5.0 5.1 Fastovsky, David E.; Sheehan, Peter M. (March 2005). "The Extinction of the Dinosaurs in North America". GSA Today 15 (3): 4–10. Retrieved 2017-04-22. 
  6. 6.0 6.1 MacLeod N. et al. (1997). "The Cretaceous–Tertiary biotic transition". Journal of the Geological Society 154 (2): 265–292. doi:10.1144/gsjgs.154.2.0265. 
  7. Chatterjee, Sankar et al 2003. Paper No. 60-8, Seattle Annual Meeting of Geological Society of America. The Shiva Crater: implications for Deccan volcanism, India-seychelles rifting, dinosaur extinction, and petroleum entrapment at the K/T boundary.
  8. Mullen, Leslie 2004. Astrobiology Magazine.Deep impact -- Shiva: another K-T impact?