The world starts to cool
After tens of millions of years of greenhouse warmth, temperatures fall towards an ice age.
- When
- Known to
- ± 10 million years
- Era
- Ordovician, Paleozoic
Carbon dioxide is drawn down through the Middle and Late Ordovician by mountain weathering, the spread of early land plants, and possibly by dust from the L-chondrite breakup shading the planet. Tropical sea temperatures fall substantially. The cooling sets up the conditions for the Hirnantian glaciation, and with it the extinction that ends the period.