Temperature: 18 °C
Atmospheric oxygen: 26%

The Paleogene is the first period of the Cenozoic Era. This period consists of Paleocene, Eocene, and Oligocene epochs. The end of the Paleocene (about 55 million years ago) was marked by the Eocene Thermal Maximum, one of the most important periods of global change during the Cenozoic. The global climate during the Paleogene began a cooling and drying trend, periodically disrupted by warm periods. The trend was caused partially by the formation of the Antarctic Circumpolar Current, which significantly lowered oceanic water temperatures.
During this time, India began to collide with Asia forming the Tibetan plateau and the Himalaya Mountains. Australia, which had been attached to Antarctica, began to move rapidly northward.