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File:Blakey 105moll.jpg
105 million years ago during the Cretaceous
White cliffs of Dover
The impressive skull of a mosasaur, a giant marine reptile of the Cretaceous.

The Cretaceous period was the longest period in the Phanerozoic eon, lasting 80 million years from 145 to 66 million years ago (mya). It followed the Jurassic period, and is the last period of the Mesozoic era. After it came the Cainozoic era.[1]

Though famous for its land fauna, the Cretaceous sea level rose much higher than today. North America was partly covered by an epicontinental sea, and half of Britain was under water. In the Upper Cretaceous, chalk, a type of limestone, was laid down in warm shallow seas. Chalk is 95% to 99% made up of coccoliths, the calcium carbonate (CaCO3) plates which tiny single-celled algae (coccolithophorids) produce.

At its end came the famous meteorite strike which, with the volcanic flood basalts spewed out in the Deccan (India), ended so many of the dominant life-forms: see K/T extinction event.

The Cretaceous period has just two very long epochs:

The Lower Cretaceous at ~45 million years, is the longest epoch in the Phanerozoic eon.


  1. Levin, Harold 2006. The Earth through time. Wiley, Hoboken N.J. Chapters 13 & 14