Tertiary Period

Tertiary Period, span of geologic time within the Cenozoic Era, no longer officially recognized. The Tertiary extended from about 65 million to about 1.8 million years ago, from the end of the Cretaceous Period of the Mesozoic Era to the beginning of the Quaternary Period of the Cenozoic Era. The Tertiary included the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs. Most scientists now consider the first three epochs of the Tertiary to be part of the Paleogene Period, and the last two to be part of the Neogene Period, but the Tertiary still appears in some scholarly literature. See Geology.