The Proterozoic Eon, spanning from 2,500 million to 539 million ... two severe glaciations known as Snowball Earth events. These ice ages, occurring between 720 and 635 million years ago, encased ...

During the Proterozoic era, oxygen produced by photosynthesizing ... future extinctions of other organisms. Did you know? An ice age is characterized by intervals of repeated glacial advances ...

The subsequent Archean eon (approximately 3,500 million years ago) is known as the age of bacteria and archaea. The Proterozoic eon was the gathering up of oxygen in Earth's atmosphere ...