Eocene-Oligocene Extinction (34 million years ago)

The Eocene-Oligocene Extinction 34 million years ago triggered an 8°C global temperature drop, transforming lush forests into open grasslands faster than the average icehouse transition—a cooling rate 4x faster than the #10 event’s climatic shift. This mass die-off eliminated 50% of tropical marine mollusks and numerous terrestrial species, but simultaneously gave rise to modern fauna like horses, dogs, and grasses. The rapid turnover outpaced the Great Oxygenation Event’s environmental change by a factor of 4, making it the swiftest climatic upheaval since that catastrophic oxygen surge.