The Early Eocene (Ypresian) is thought to have had the highest mean annual temperatures of the entire Cenozoic, with temperatures about 30° C; relatively low temperature gradients from pole to pole; and high precipitation in a world that was essentially ice free. Land connections existed between Antarctica and Australia, between North America and Europe through Greenland, and probably between North America and Asia through the Bering Strait. It was an important time of plate boundary rearrangement, in which the patterns of spreading centers and transform faults were changed, causing significant effects on oceanic and atmospheric circulation and temperature.
In the middle Eocene, the separation of Antarctica and Australia created a deep water passage between those two continents, creating the circum-Antarctic Current. This changed oceanic circulation patterns and global heat transport, resulting in a global cooling event observed at the end of the Eocene.
By the Late Eocene, the new ocean circulation resulted in a significantly lower mean annual temperature, with greater variability and seasonality worldwide. The lower temperatures and increased seasonality drove increased body size of mammals, and caused a shift towards increasingly open savanna-like vegetation, with a corresponding reduction in forests.
Find out more about the Tertiary paleontology and geology of North America at the Paleontology Portal.
Elasmo.com has a world map for the Middle Eocene, showing continental placement and sealevel.
For additional maps of the Eocene world, visit the Eocene page at the Paleogeography Through Geologic Time site by Dr. Ron Blakey of Northern Arizona University.
You can also read about the Chesapeake Bay Bolide Impact of the Late Eocene. The USGS provides a study of how this spectacular meteorite impact affected the geology and natural history of Eastern North America.