Definition of Cretaceous–Tertiary boundary in US English:

Cretaceous–Tertiary boundary

(also K/T boundary)

proper noun

  • The division between the Cretaceous and Tertiary periods, about 65 million years ago.

A widespread layer of sediment dating from this time has been shown since 1980 to be enriched in iridium and other elements and carbon deposits indicative of extensive fires. This appears to indicate the catastrophic impact of one or more large meteorites, and geologists have identified a formation at Chicxulub in the Yucatán Peninsula, Mexico, as a probable impact site. A resulting drastic climate change has been suggested as the cause of the extinction of dinosaurs and many other organisms at this time, but this remains controversial