Pleistocene

The Pleistocene ( PLY-stə-seen, -⁠stoh-; referred to colloquially as the Ice Age) is the geological epoch that lasted from c. 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in 2009 by the International Union of Geological Sciences, the cutoff of the Pleistocene and the preceding Pliocene was regarded as being 1.806 million years Before Present (BP). Publications from earlier years may use either definition of the period. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology. The name comes from Ancient Greek πλεῖστος (pleîstos), meaning "most", and καινός (kainós), meaning "new, recent".

The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was highly variable depending on the glacial cycle, oscillating between cold glacial periods and warmer interglacials, with sea levels dropping at peak glaciation by as much 120 metres (390 ft) lower than present, allowing the periodic connection of Asia and North America via the Beringia land bridge, and the covering of most of northern North America by the large Laurentide Ice Sheet.

At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia. The end of the Early Pleistocene is marked by the Mid-Pleistocene Transition, with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme.