Cretaceous is the name given to a period of time in Earth's history (i.e., Cretaceous Period) from 145.6 to 65 million years ago. Also, all the rocks that formed during that time have the same proper name of Cretaceous (i.e., they are referred to as the Cretaceous System). Said differently, the Cretaceous System is the rock record of events that occurred—and organisms that lived—during a span of geological time that is called Cretaceous Period. Cretaceous was the third and final period of the Mesozoic Era.

Cretaceous is a name derived from the Latin word for chalk, creta. Chalk is a common type of sedimentary rock formed during this interval of Earth history. The term Cretaceous was first used in 1822 by d'Omalius d'Halloy (1707–1789), a Belgian geologist who was engaged in pioneering efforts at geological mapping of parts of France. He mapped the Terrain Cretac (Cretaceous...