The Pleistocene (symbol PS) is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's recent period of repeated glaciations.
Charles Lyell introduced this term in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" ("Most New" or "Newest") from the Greek πλεῖστος, ''pleīstos'', "most", and καινός, ''kainós'' (latinized as ''cænus''), "new";〔(【引用サイトリンク】url=http://www.etymonline.com/index.php?term=Pleistocene&allowed_in_frame=0 )〕 this contrasting with the immediately preceding Pleiocene ("More New" or "Newer", from πλείων, ''pleíōn'', "more", and ''kainós''; usual spelling: Pliocene), and the immediately subsequent Holocene ("wholly new" or "entirely new", from ὅλος, ''hólos'', "whole", and ''kainós'') epoch, which extends to the present time.
The Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era.〔 ''In'' Gradstein, F. M., Ogg, James G., and Smith, A. Gilbert (eds.), ''A Geologic Time Scale 2004'' Cambridge University Press, Cambridge, ISBN 0-521-78142-6〕 The end of the Pleistocene corresponds with the end of the last glacial period. It also corresponds with the end of the Paleolithic age used in archaeology. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Calabrian, Ionian and Tarantian. All of these stages were defined in southern Europe. In addition to this international subdivision, various regional subdivisions are often used.
Before a change finally confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years before the present, as opposed to the currently accepted 2.588 million years BP: publications from the preceding years may use either definition of the period.
The Pleistocene has been dated from 2.588 million (±.005) to 11,700 years before present (BP), with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP.〔For the top of the series, see: , (2004) "The Neogene Period". In: Gradstein, F., Ogg, J., Smith, A.G. (Eds.), ''A Geologic Time Scale 2004''. Cambridge: Cambridge University Press.〕 It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell. The end of the Younger Dryas has been dated to about 9640 BC (11,654 calendar years BP). It was not until after the development of radiocarbon dating, however, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites.
In 2009 the International Union of Geological Sciences (IUGS) confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, and accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.〔Riccardi, Alberto C. (30 June 2009)
("IUGS ratified ICS Recommendation on redefinition of Pleistocene and formal definition of base of Quaternary" ) International Union of Geological Sciences〕 The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point (GSSP), for the upper Pleistocene/Holocene boundary (''i.e.'' the upper boundary). The proposed section is the ''North Greenland Ice Core Project'' ice core 75° 06' N 42° 18' W.〔Svensson, A., S. W. Nielsen, S. Kipfstuhl, S. J. Johnsen, J. P. Steffensen, M. Bigler, U. Ruth, and R. Röthlisberger (2005) "Visual stratigraphy of the North Greenland Ice Core Project (NorthGRIP) ice core during the last glacial period" ''Journal of Geophysical Research'' 110: (D02108)〕 The lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: ''Discoaster pentaradiatus'' and ''Discoaster surculus''.〔Gradstein, Felix M.; Ogg, James G. and Smith, A. Gilbert (eds.) (2005) ''A Geologic Time Scale 2004'' Cambridge University Press, Cambridge, UK, p. 28, ISBN 0-521-78142-6〕
The Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has in the past been used to mean the last ice age. The revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene.
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