The Proterozoic is the portion of the Precambrian running from about 2,500 million to about 542 million years ago. It is divided into three eras: Paleoproterozoic (2,500–1,600 million years ago), Mesoproterozoic (1,600–1,000 million years ago), and Neoproterozoic (1,000–542 million years ago).


Especially significant events that occurred during the Proterozoic eon were the development of an oxygenated atmosphere during the Mesoproterozoic; several glaciations, including a hypothesized Snowball Earth during the Cryogenian period in the late Neoproterozoic; and, the evolution of abundant soft-bodied multicellular organisms during the Ediacaran period.