The Eocene-Oligocene extinction event was one of the most significant events in Earth’s history, resulting in the loss of over half of all species on the planet. This mass extinction occurred during a time when Earth was going through a major transition, from the warm, wet conditions of the Eocene to the cooler, drier conditions of the Oligocene. The cause of this extinction event is still debated by scientists, but it is thought to be due to a combination of factors, including climate change, volcanic activity, and changes in sea level.
The Eocene-Oligocene boundary marks the end of the Eocene epoch and the beginning of the Oligocene epoch. The Eocene was characterized by warm global temperatures and high sea levels. The Oligocene, on the other hand, was a time of cooling temperatures and falling sea levels. This transition between epochs was gradual at first, but around 33 million years ago (mya), there was a sharp decline in temperature known as the Grande Coupure. This rapid cooling led to drastic changes in Earth’s climate and ecosystems.
One theory for why so many species went extinct during this time is that they simply could not adapt to these new conditions quickly enough. Another possibility is that certain keystone species were lost which caused widespread ripple effects throughout entire ecosystems. For example, if large predators went extinct then their prey would have flourished without competition leading to an imbalance in those populations as well. Changes in sea level also played a role in this extinction event since many shallow water habitats were lost as well as coastal forests being inundated with salt water.
Volcanic activity may also have been partly responsible for causing such dramatic climate changes during this time period. The eruption of Toba supervolcano around 74 mya is thought to have had global consequences and cooled average temperatures by up to 10°C (18°F) for several years afterwards. However, it is difficult to determine how much impact any single factor had on causing this mass extinction event since it likely was a combination of several different things happening all at once.