These two snowball earth events were previously put together as the "Varangian" glaciation. They covered much, possible all, the Earth with ice. The root cause of the temperature drop may have been the removal of CO from the atmosphere by photosynthesising bacteria and eukaryotes in the previous periods. 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.