1. The Cretaceous-Tertiary extinction event, which occured approximately 65.5 million years ago, 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 ( a historical term for the period of time now covered bt the Paleogane and Neogene periods). The event marks the ends of the
Mesozoic Era and the beginning of the Cenozoic Era. With " Tertiary" being discourged as a formal time or rock unit by the International Commission on Stratigrapy, the K-T event is now called the Cretaceous-Paleogene (or K-PG) extinction event by many researchers.
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