Eocene–Oligocene extinction event facts for kids

The end of the Eocene epoch marked the start of the Oligocene epoch, about 33.9 million years ago. This time saw a huge change in both plants and animals across the world. Many species disappeared, and new ones took their place.

Most of the creatures affected lived in the ocean or in fresh water. This included the last of the ancient whales, known as Archaeoceti. These were early forms of whales that lived long ago.

What Caused This Big Change?

This period was a time of major climate change. The Earth became much cooler. Scientists first thought this cooling wasn't caused by one big event, like a huge volcanic eruption or a giant meteorite hitting Earth.

Volcanic Activity and Meteorite Impacts

However, some scientists now think that volcanic activity might have played a role in these extinctions. Also, several very large meteorite impacts happened around this time.

One impact created the Chesapeake Bay impact crater, which is about 40 kilometers (25 miles) wide. Another impact formed the Popigai crater in central Siberia. This crater is even bigger, about 100 kilometers (62 miles) wide! When these meteorites hit, they scattered rocks and dust far and wide, possibly even reaching Europe. Recent studies suggest the Popigai meteor impact might have been a major cause of the mass extinction.

The Role of Carbon Dioxide

One leading idea about the cooling climate involves carbon dioxide in the air. Scientists believe that the amount of carbon dioxide in Earth's atmosphere slowly went down during the late Eocene. Around 34 million years ago, it might have dropped below a certain level.

This drop in carbon dioxide is linked to an event called the Oligocene Oi-1 event. This event shows a change in oxygen isotopes, which are like different versions of oxygen atoms. This change marks the beginning of large ice sheets forming on Antarctica. Less carbon dioxide in the air can lead to a cooler planet and more ice.