Proterozoic

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 2500 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
 * 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.