This article is about the geologic period. For base-4 in mathematics, see quaternary numeral system.

The Quaternary Period is the geologic time period from the end of the Pliocene Epoch roughly 1.8-1.6 million years ago to the present. The Quaternary includes 2 geologic subdivisions -- the Pleistocene and the Holocene Epochs.

The term Quaternary ("fourth") was proposed by Jules Desnoyers in 1829 to address sediments of France's Seine Basin that seemed clearly to be younger than Tertiary Period rocks. The Quaternary Period follows the Tertiary Period and extends to the present. The Quaternary roughly covers the time span of recent glaciations, including the last glacial retreat. An occasional alternative usage places the start of the Quaternary at the onset of North Pole glaciation approximately 3 million years ago and includes portions of the upper Pliocene. Some people do not recognize the Quaternary and consider it an informal term included in the Neogene, as can be seen from the 2003 edition of the International Stratigraphic Chart, published by the International Commission on Stratigraphy.

The 1.8-1.6 million years of the Quaternary represents the time during which recognizable humans existed. Continental drift of less than 100km is largely irrelevant to such a short time period. The climate was one of periodic glaciations with continental glaciers moving as far from the poles as 40 degrees latitude. Few major new animals evolved, again presumably because of the short -- in geologic terms -- duration of the period. There was a major extinction of large mammals in Northern areas at the end of the Pleistocene Epoch. Many forms such as the sabertooth cat, mammoths, mastodons, glyptodonts, etc., became extinct worldwide. Others, including horses, camels and cheetahs became extinct in North America.