Pleistocene

\n

\nThis epoch is part of the Quaternary period.\n

Paleolithic\n

Holocene\n

Pleistocene\n

The Pleistocene epoch is part of the geologic timescale, usually dated as 1.8-1.6 million to 10,000 years before present, with the end\ndate expressed in radiocarbon years. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold\nperiod that interrupted the final deglaciation. The end of the Younger Dryas has been dated to about 9600 BC (11550 calendar years BP). The GSSP for the start of the Pleistocene is in a reference section at Virca in Italy that has unresolved dating ambiguities. The Pleistocene follows the Pliocene Epoch and is followed by the Holocene Epoch.\nThe Pleistocene is the first of the two epochs of the Quaternary Period or 6th epoch of the Cenozoic Era. As with other older geologic periods, the rock beds that define the start of the Pleistocene are well identified, but the exact dates of the start and end of the period are slightly uncertain.\nThe Pleistocene was originally intended to cover the recent period of repeated glaciations, however, the start was set too late and some early cooling and glaciation are now set in the Pliocene. Some would prefer a start date of around 2.5 million years BP. There are no Faunal stages defined for the Pleistocene or Holocene. Continents were at essentially their modern positions during the Pleistocene probably moving no more than 100km at most.\nThe Pleistocene climate was characterized by repeated glacial cycles where continental glaciers pushed to the 40th parallel in places.\nFour major glacial events have been identified as well as many minor intervening events.\nThe four major identified glacial excursions were the Nebraskan-Gunz, Kansan-Mindel, Illinoian-Riss, and Wisconsin-Wurm.\nThere may have been as many as 14 additional unnamed advances whose results have been largely erased by the later glaciers.\nEach glacial advance tied up huge volumes of water in continental ice sheets 1500-3000 meters thick resulting in temporary sea level drops of 100 meters or more.\nAntarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene Period. Both marine and continental faunas were essentially modern. Humans evolved into modern man during the Pleistocene.\nMajor extinctions of large mammals including mammoths, mastodons, sabertoothed cats and giant sloths started late in the Pleistocene and continued into the Holocene.\nThe extinctions were especially severe in North America where native horses and camels were eliminated. Pleistocene continental deposits are found primarily in lakebeds and caves as well as in the large amounts of material moved about by glaciers.\nPleistocene marine deposits are found primarily in areas within a few tens of kilometers of the modern shoreline.\nIn a few geologically active areas such as the Southern California Coast, Pleistocene marine deposits may be found at elevations of several hundred meters. The end of the Pleistocene corresponds with the end of the Paleolithic age used in archaeology.

See also: Geologic Time Scale

Category:Geologic timescale\n\n\n\n\n\nzh-cn:更新世