The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. 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 Me… (More on Proterozoic)