The Proterozoic consists of 3 geologic eras, from oldest to youngest: * Paleoproterozoic * Mesoproterozoic * Neoproterozoic The well-identified events were: * The transition to an oxygenated atmosphere during the Mesoproterozoic. * Several glaciations, including the hypothesized Snowball Earth during the Cryogenian period in the late Neoproterozoic. * The Ediacaran Period (635 to 542 Ma) which is characterized by the evolution of abundant soft-bodied multicellular organisms.