The Paleogene Period is the oldest division of the Cenozoic Era and spans from 66 to 23 million years ago. Its name comes from the Greek words meaning “ancient-born.” This period marks the recovery of life after the Cretaceous extinction, leading to the rapid diversification of mammals, birds, and flowering plants.
One of its major subdivisions, the Eocene Epoch, comes from the Greek eos, meaning “dawn,” symbolizing the appearance and expansion of many modern groups of organisms such as mammals and mollusks. During this time, archaic primates from the earlier Paleocene began to decline as their ecological roles were replaced by more efficient rodents. The Paleogene set the stage for the rise of many animal groups that dominate ecosystems today.
The Neogene Period extends from 23 million to 2.6 million years ago, and its name means “newborn.” It was given this name because the fossils found in Neogene rocks show animals and plants that are more closely related to modern species than those of the Paleogene. During the Neogene, mammals and birds continued to evolve and spread across the globe, while grasslands expanded, leading to the rise of grazing animals and their predators. Oceans and continents continued shifting into the positions they occupy today. Many modern plant and animal families became well established during this time, giving the period a distinctly “modern” feel in the fossil record.
The Quaternary Period is the most recent division of geologic time, beginning 2.6 million years ago and continuing to the present. It is characterized by repeated cycles of glaciation—commonly known as the Ice Ages—during which massive ice sheets covered large portions of the continents. These rapid climate shifts caused major changes in sea levels, ecosystems, and the distribution of plants and animals.
The Quaternary is especially significant because it includes the rise of modern humans, beginning around 200,000 years ago. It is also one of the best-studied periods due to the excellent preservation of its geological record.
The period contains famous ice-age animals such as woolly mammoths, sabre-toothed cats, and cave bears—species now extinct but well documented in fossils and exhibits. Much of what scientists know about Quaternary environments comes from plant fossils, especially pollen, which helps track past climates, glacial retreats, and changes in vegetation zones.
These shifts reflect how plants adapted gradually to long-term changes in temperature and humidity. The term Quaternary originated in the 19th century, when French geologist Jules Desnoyers used it to label the youngest deposits in the Paris Basin, following the old system of naming geologic eras as Primary, Secondary, Tertiary, and so on.