1) Ice age 
The Cryogenian (from Greek cryos `cold` and genesis `birth`) is a geologic period that lasted from {Mya|850 |635}. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran. The Sturtian and Marinoan glaciations, which are the greatest ice ages known to have occurred on Earth, oc...