~720–635 million years agoReputable sourceWell documented
Snowball Earth
On the timeline · around ~720–635 million years ago · Proterozoic
What happened
During the Cryogenian period, the planet endured at least two extreme global glaciations — the Sturtian and Marinoan — when ice may have reached the equator and average temperatures plunged far below freezing. Life survived in refuges such as meltwater ponds.
Why it matters
The dramatic climate upheavals of 'Snowball Earth' immediately preceded the rise of the first complex animals, and may have helped drive their evolution.