Geologic Time Scale: Cretaceous Aptian Stage
(121.4 to 113.0 million years ago)
The Cretaceous Period is the third and final period of the Mesozoic and the longest period of the Phanerozoic Eon. The period as first defined by Belgian geologist Jean d’Omalius d’Halloy in 1822 as the Terrain Cretace, using starta (layers) in the Paris Basin and names for the extensive beds of chalk(calcium carbonate deposited by the shells of marine invertebrates, principally coccoliths), found in the upper Cretaceous of Western Europe. The name is derived from the Latin creta meaning “chalk”, which is abundant in the later half of the period.
During the Cretaceous, the late-Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into the present-day continents, although their positions were substantially different at the time. The Earth’s Climate was warmer than today, and sea level was much higher. The end of the Cretaceous period (along with the Mesozoic) ended with the Cretaceous-Paleogene extinction event (formerly known as the KT boundary).