A Tertiary landscape with volcanoes and lava fields

Oligocene epoch

Over 30 million years ago, the Oligocene epoch saw the start of the global cooling that would eventually shift the Earth's climate to one where glaciers were present and ice ages were possible. Worldwide, this was the time when grasslands began to expand and forests - especially tropical ones - shrank correspondingly. Animals evolved to fit the new, open landscape and many fast-running prey and predator species arose as a result.

Began: 33.7 million years ago

Ended: 23.8 million years ago

What the Earth was like

A map of the Earth in the Oligocene Epoch

Reconstruction of the Earth in the Oligocene epoch, 33.7 million - 23.8 million years ago. Credit: Dr Ron Blakey, NAU Geology.

Causes of extinctions

During this period the following extinction level events are thought to have occurred.

Climate change Climate change
Earth's climate is not constant. Over geological time, the Earth's dominant climate has gone from ice age to tropical heat and from steamy jungles to searing deserts.

Types of fossils formed in this period