Chlorellopsis coloniatathe Stromatolite, Eocene, United States

Eocene Information

The Eocene Period (56–33.9 million years ago) was a time of warm global temperatures and the rapid evolution of mammals following the extinction of the dinosaurs. The climate was hot and humid, with lush rainforests covering much of the planet, even near the poles. Mammals diversified into new ecological roles, with early primates, whales (like Basilosaurus), large herbivores, and carnivores emerging. Birds and reptiles also thrived, and the first grasses began spreading, setting the stage for later grassland ecosystems. By the late Eocene, the Earth’s climate cooled significantly, leading to the formation of the first Antarctic ice sheets and the eventual transition to the drier, cooler Oligocene Period.