Ordovician-Silurian Extinction (445 million years ago)

The Ordovician-Silurian Extinction, driven by rapid glaciation, caused sea levels to plummet by 80 meters, destroying shallow marine habitats and killing 85% of marine species. As the first of the 'Big Five' mass extinctions, it was 5% more effective than the Late Devonian Extinction in marine species loss, though 11% slower than the Permian-Triassic Extinction in total extinction rate. Its glacial trigger made it a unique 80-meter sea-level drop event.