The long cooling begins
From the Eocene peak, the planet starts a 50-million-year slide that ends in the ice ages.
- When
- —
- Duration
- 14 million years
- Known to
- ± 2 million years
- Era
- Eocene, Cenozoic
After the Early Eocene optimum, deep-sea oxygen isotopes record a nearly continuous decline in global temperature that runs, with interruptions, to the present. The drivers are debated and probably layered: silicate weathering of the rising Himalaya consuming carbon dioxide, organic burial such as the Azolla event, declining volcanic outgassing, and the gradual opening of Southern Ocean gateways. Whatever the mix, the Cenozoic has two halves — a hot one and a cold one — and the hinge is here.