THE LATE EOCENE-OLIGOCENE EXTINCTIONS

The Eocene-Oligocene extinctions took place over about 10 million years, starting with a major extinction in tropical organisms at the end of the middle Eocene, and followed by a significant global cooling event and a lesser extinction event in the earliest Oligocene. Very minor extinctions occurred in the late Eocene and in the mid-Oligocene. In spite of the evidence of four impacts around 35-36 Ma, no short-term extraterrestrial events or volcanic eruption is sufficient to explain this pattern of extinction. The overwhelming evidence for global cooling and oceanic circulation changes argue that these must have been the proximal cause of extinction. The likely triggers of this cooling were the development of the circum-Antarctic current and the opening of the Norwegian-Greenland Sea. -from Author