The end-Ordovician mass extinction
The second-deadliest extinction in history kills roughly 85% of species — in two separate pulses.
- When
- —
- Duration
- 1.9 million years
- Known to
- ± 2 million years
- Era
- Ordovician, Paleozoic
Between about 445 and 443 million years ago marine life is devastated twice over: first as glaciation drains the shelves and cools the oceans, then again as the ice melts, sea level rebounds and anoxic water floods back across the shelves. Around 85% of species and more than half of all genera are lost. Trilobites, brachiopods, graptolites and the giant nautiloids are hit hardest. Recent work ties the severity to the sheer rate of climate change rather than its magnitude.