65 milion years ago (mya) the Cenozoic Era began in the time-scale of geological units. Each Era is divided into Periods of time, and each Period of the Cenozoic Era is divided into Epochs of time. Please click on the link below for a diagram of the Periods and Epochs in the Cenozoic Era, and for important information about the rise of the Mammals. This link below shows that the last Ice Age ended 10,000 years ago and the time period (epoch) since then is called the Holocene Epoch. There has been a series of “ice ages” over billions of years, with the “Great Ice Age” occurring during the Pleistocene Epoch of the Cenozoic Era, 1.8 million to 10,000 years ago.
The dinosaurs had become extinct and now it was the Age of the Mammals, arising in the Palaeocene Epoch of the Cenozoic Era, 65 to 55 mya; with the modern line of human beings (from the genus Homo) developing 1.6 mya to 2 mya. During the Pleistocene Epoch of the Cenozoic Era, there were four completely separate glacial advances in North America. The advances were separated by long intervals of ice withdrawal, sufficient to permit the previously occupied area covered by ice to be reoccupied by plants and animals. Glaciation severely affected life on the earth. Animal and plant life was forced out of vast portions of the land covered by continental ice sheets. Large-scale migrations must have taken place as the ice sheets grew and climatic changes occurred.
Click here to see some wonderful preserved skeletons of some of the “mega-fauna” (large mammals) of the Pleisotcene Epoch (1.8 mya to 10,000 years ago).