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K–T boundary

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Badlands near Drumheller, Alberta where erosion has exposed the KT boundary.

The K–T boundary is a geological signature, usually a thin band, dated to (65.5 ± 0.3) Ma.[1] K is the traditional abbreviation for the Cretaceous period, and T is the abbreviation for the Tertiary period. The boundary marks the end of the Mesozoic era and the beginning of the Cenozoic era, and is associated with the Cretaceous–Tertiary extinction event, a mass extinction.[2] With "Tertiary" being discouraged as a formal time or rock unit by the International Commission on Stratigraphy, the K–T extinction event is now called the Cretaceous–Paleogene (or K–Pg) event by many researchers.[3]


  1. ^ "International Stratigraphic Chart" (pdf). International commission for Stratigraphy. 2008. Retrieved on 2008-12-24. 
  2. ^ Fortey, R (1999). Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage. pp. 238–260. ISBN 978-0375702617. 
  3. ^ Gradstein F, Ogg J, Smith A. A Geologic Time Scale 2004. 

Cretaceous–Tertiary extinction event
Proposed K-T boundary craters
Boltysh crater Chicxulub Crater
Shiva crater Silverpit crater
Mantell's Iguanodon restoration

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