Proterozoic

The eon spanning from about 2.5 billion to 541 million years ago, covering the rise of atmospheric oxygen, the appearance of complex single celled and early multicellular life, and several major global glaciations. Includes the Proterozoic eon itself, its three constituent eras (Paleoproterozoic, Mesoproterozoic, Neoproterozoic), and every period nested within those eras in the standard geologic time scale: Siderian, Rhyacian, Orosirian and Statherian under the Paleoproterozoic; Calymmian, Ectasian and Stenian under the Mesoproterozoic; and Tonian, Cryogenian and Ediacaran under the Neoproterozoic. Belongs here: the Proterozoic eon and any era or period formally nested inside it. Does not belong here: the Phanerozoic eon that follows, defined by the abundant animal fossil record the Proterozoic itself predates, or the Archean eon that precedes it.