The Eocene Epoch, lasting from about 56 to 34 million years ago (55.8 ± 0.2 to 33.9 ± 0.1 Ma), is a major division of the geologic timescale and the second epoch of the Palaeogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by the emergence of the first modern mammals.
