Cryogenian
These two snowball earth events were previously put together as the Varangian glaciation. They covered much, possibly all, the Earth with ice. The root cause of the temperature drop may have been the removal of CO2 from the atmosphere by photosynthesising bacteria and eukaryotes in the previous Great Oxygenation Event. Much else happened: the supercontinent Rodinia broke up and another, Pannotia, began to form. Fossil steroids suggest the presence of early sponges, and amoeboid cells with tests (coverings) appear in the fossil record.