Sturtian glaciation, Cryogenian period. Illustration showing the Earth during a glaciation in the Cryogenian period. This geologic period lasted from 850 to 635 million years ago, and included several global glaciations covering the entire Earth (the 'Snowball Earth' hypothesis). This is the Earth at the start of the Sturtian glaciation (750 to 700 million years ago), with the Rodinia supercontinent beginning to break up. Such glaciations killed most life, but when they ended the survivors exploded in evolutionary diversity.