The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life". The Proterozoic Eon extended from 2,500 Ma to 542.0±1.0 Ma (million years ago), and is the most recent part of the old, informally named ‘Precambrian’ time. The Proterozoic consists of 3 geologic eras, from oldest to youngest: Paleoproterozoic, Mesoproterozoic and 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.