The great thaw
As the ice melts, a layer of carbonate is laid down worldwide in a geological instant.
- When
- Known to
- ± 3 million years
- Era
- Neoproterozoic, Proterozoic
Directly above Cryogenian glacial deposits, on every continent, sits a distinctive cap carbonate tens of metres thick. It records the aftermath of snowball collapse: an atmosphere loaded with volcanic carbon dioxide, torrential acidic rain stripping the continents, and carbonate precipitating from a hot, alkaline ocean. Their global synchroneity is among the strongest arguments that the glaciations really were planet-wide.