CLIMATE × EARTH

Snowball Earth

~717 to 635 million years ago

Proterozoic · Neoproterozoic · Cryogenian

Twice in the Cryogenian, ice sheets thick enough to rest on the seabed reached sea level at every latitude, the tropics included. The two were not alike: the first, the Sturtian, lasted 56 million years; the second, the Marinoan, about four. Between them the planet had twenty million years of open water at most, and it is in that window that algae displaced bacteria at the head of production in the open sea.

Why it matters

Life went through the harshest climate the planet has produced and came out reorganised. The short gap between the two freezes is when algae move in at the base of the marine food web, and the brevity of the second freeze may be the reason animals were still there to inherit the result.

Dating & uncertainty

Two distinct glaciations rather than one: the Sturtian lasted about 56 million years, the Marinoan closer to four. The bounds come from uranium-lead and rhenium-osmium ages on the rocks that bracket the glacial deposits.

Sources

1. Hoffman et al. (2017), Science Advances · Snowball Earth climate dynamics and Cryogenian geology-geobiology
2. Tasistro-Hart et al. (2025), PNAS · Four-million-year Marinoan snowball shows multiple routes to deglaciation
3. Prave et al. (2016), Geology · Duration and nature of the end-Cryogenian (Marinoan) glaciation
4. Brocks et al. (2017), Nature · The rise of algae in Cryogenian oceans and the emergence of animals

Earth history as one day

20:12:343 h 47 min before midnight

if Earth’s 4.54 billion years were compressed into a single day