Snowball Earth

The phase of extensive glaciation referred to as "Snowball Earth" is the second major ice age in Earth's history. The first, described in Station 2, was triggered by the initial presence of oxygen in the atmosphere.

The second phase, described here, was likely initiated by the breakup of the then-existing supercontinent Rodinia. This breakup allowed precipitation to reach regions that had previously been dry and desert-like due to the supercontinent's vast size. Consequently, the rocks in these areas were exposed to chemical weathering, which converted atmospheric carbon dioxide into limestone and led to its deposition. The removal of this greenhouse gas from the atmosphere caused temperatures to drop, resulting in glaciation. Volcanic activity later reintroduced carbon dioxide into the atmosphere, which then contributed to the thawing of the ice.

There were at least four glaciations during this period, with at least two affecting the entire planet. The details of these events are still the subject of ongoing research. However, we know that this period saw the evolution of multicellular organisms. Although there are no direct fossils from this time, molecular clocks—derived from comparisons of DNA sequences—suggest that all extant lines of multicellular life originated during this period. This likely includes the now-extinct lines as well, indicating that the diversity of life reached its peak during this time.