Snowball Earth episodes

In the late Neoproterozoic, Earth experienced at least two exceptionally extensive glaciations, the Sturtian and Marinoan. Evidence places ice at low latitudes, supporting the widely discussed near-global “Snowball Earth” hypothesis, but whether the oceans were completely ice-covered remains debated. Gaskiers or Kaigas episodes are sometimes added to the list; a count of “up to four” depends on classification and does not mean four certain episodes of total planetary freeze-over.