Temperature: 14 °C
Atmospheric oxygen: 21.5%

The Neogene is a period that spans 20.45 million years. It is sub-divided into two epochs, the earlier Miocene and the later Pliocene. The Isthmus of Panama connected North and South America later in the Pliocene, cutting off the Atlantic Ocean from the warm ocean currents from the Pacific, and leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary period that follows.
20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly. The world has taken on a “modern” look, but notice that Florida and parts of Asia were under water.