Last modified on 13 April 2010, at 11:00

Introduction to Geochronology/Cretaceous-Paleogene Boundary

Badlands near Drumheller, Alberta, where erosion has exposed the K–T boundary


The Cretaceous–Tertiary extinction event, which occurred approximately 65.5 (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. Widely known as the K–T extinction event, it is associated with a geological signature known as the K–T boundary, usually a thin band of sedimentation found in various parts of the world. K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit, and T is the abbreviation for the Tertiary Period. The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era.[1] 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–Paleogene (or K–Pg) extinction event by many researchers.[2]

  1. Fortey, R (1999). Life: A Natural History of the First Four Billion Years of Life on Earth. Vintage. pp. 238–260. ISBN 9780375702617. 
  2. Gradstein, F; Ogg J, Smith A. A Geologic Time Scale 2004. http://www.cambridge.org/uk/catalogue/catalogue.asp?isbn=0521781426.