Cretaceous

The Cretaceous (pronounced /kriːˈteɪʃəs/, usually abbreviated 'K' for its German translation "Kreide") is a geologic period and system, reaching from the end of the Jurassic Period, (145.5 ± 4 million years ago (Ma) to the beginning of the Paleocene Period, 65.5 ± 0.3 Ma. It is the youngest geological period of the Mesozoic, and at 80 million years long, the longest period of the Phanerozoic. The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras. The Cretaceous (from Latin creta meaning 'chalk' ) as a separate period was first defined by a Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris Basin and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous of continental Europe and the British Isles (including the White Cliffs of Dover). As with other older geologic periods, the rock beds that define the Cretaceous are well identified but the exact dates of the period's start and end are uncertain by a few million years. No great extinction or burst of diversity separated the Cretaceous from the Jurassic.

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