Geologic history of the earth; divided into ages.

CENOZOIC - The age of mammals
From approximately 63 million years ago to the present age. Composed of the Quaternary and Tertiary periods. The Quaternary period is comprised of the Holocene and Pleistocene Epochs. The Tertiary period is comprised of the Pliocene, Miocene, Oligocene, Eocene, and Paleocene Epochs.

MESOZOIC - The age of reptiles
From approximately 240 million years ago to 63million years ago.
Composed of the Cretaceous, Jurassic, and Triassic periods

PALEOZOIC - The age of fishes
From approximately 550 million years ago to 240million years ago.
Composed of the Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, and Cambrian periods

PRECAMBRIAN
From approximately 4500 million (4.5 billion) years ago until 600 million years ago and the Great Unconformity. Composed of the Younger and Older periods

Source
Buncha admirable geeks.