The Hirnantian glaciation
Ice sheets bury Gondwana and sea level crashes, draining the shallow seas life depended on.
- When
- Known to
- ± 2 million years
- Era
- Ordovician, Paleozoic
Gondwana sits over the south pole, and in the final million years of the Ordovician a severe glaciation builds ice sheets across what is now North Africa and Arabia. Sea level falls sharply, emptying the vast epeiric seas that had hosted the Ordovician radiation. Glacial striations and tillites in the Sahara record ice where there is now desert.