K/T extinction event

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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, or Cretaceous–Palaeogene extinction event, was about 66 million years ago. It may be called the K/T extinction event or even 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 Cainozoic era.[1][2]

Effects[change | change source]

Dinosaur fossils are only found below the K–T boundary. This shows they became extinct before, or during the event.[3] 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.[4]

Causes[change | change source]

Scientists think the K–T extinctions were caused by one or more catastrophic events, such as massive asteroid or meteorite impacts (like the Chicxulub impact), and increased volcanic activity.

Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, have been dated to the approximate time of the extinction event. These geological events would have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology.[4]

Craters[change | change source]

Evidence is accumulating that there were multiple impacts 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.[5][6] 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.

Related pages[change | change source]

References[change | change source]

  1. Fortey R (1999). Life: A natural history of the first four billion years of life on Earth. Vintage. pp. 238–260. ISBN 0375702617 .
  2. 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. http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=0521781426.
  3. Fastovsky D.E. Sheehan P.M. (2005). "The extinction of the dinosaurs in North America". GSA Today 15 (3): 4–10. doi:10.1130/1052-5173(2005)015<4:TEOTDI>2.0.CO;2 . http://www.gsajournals.org/perlserv/?request=get-document&doi=10.1130%2F1052-5173%282005%29015%3C4%3ATEOTDI%3E2.0.CO%3B2. Retrieved 2007-05-18.
  4. 4.0 4.1 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 . http://findarticles.com/p/articles/mi_qa3721/is_199703/ai_n8738406/print.
  5. 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.
  6. Mullen, Leslie 2004. Astrobiology Magazine.Deep impact -- Shiva: another K-T impact?