On Old Earth, the second epoch of the Tertiary period and Cenozoic era, lasting from 57-34 million years ago. It was preceded by the Paleocene, and followed by the Oligocene.
Archaic mammals were common. Primates, rodents, primitive whales and many other types of mammals appeared for the first time. The Earth had a tropical climate worldwide, with palms and other warm-loving plants occurring in northern latitudes. Coral Reefs flourished in the seas. Insects, fish, reptiles, etc. were similar to modern forms.
Elsewhere in the galaxy, the Muuh are thought to have achieved space flight and interstellar travel during this time (in galactic history, the Muuhian Epoch commenced during this period, and ended in Earth's mid-Miocene) and a xenosophont BGC virch world was established at Steelcliff.