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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 date expressed in radiocarbon years. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold the final deglaciation. The end of the Younger Dryas has been dated to about 9600 BC (11550 calendar years BP).
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. 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.
Pleistocene paleogeography and climate
The modern continents were essentially at their present positions during the Pleistocene, probably moving no more than 100km. The Pleistocene climate was characterized by repeated glacial cycles where continental glaciers pushed to the 40th parallel in some places. Four major glacial events have been identified, as well as many minor intervening events. The four major identified glacial excursions were the Nebraskan-Gunz, Kansan-Mindel, Illinoian-Riss, and Wisconsin-Würm. There may have been as many as 14 additional unnamed advances whose results have been largely erased by the later glaciers. Each 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. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene.
There are no faunal stages defined for the Pleistocene or Holocene. Both marine and continental faunas were essentially modern. It is believed by most scientists that humans evolved into modern man during the Pleistocene. Major extinctions of large mammals, including mammoths, mastodons, saber-toothed cats, glyptodons and Ground sloths, started late in the Pleistocene and continued into the Holocene. The 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. Pleistocene marine deposits are found primarily in areas within a few tens of kilometers of the modern shoreline. In a few geologically active areas such as the Southern California coast, Pleistocene marine deposits may be found at elevations of several hundred meters.
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