Week3_Pleistocene

Week3_Pleistocene - 3-1Week 3: Pleistocene EpochThe...

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Unformatted text preview: 3-1Week 3: Pleistocene EpochThe Pleistocene epoch on the geologic timescale isthe period from 1,808,000 to 11,550 years BP. ThePleistocene epoch had been intended to cover theworld's recent period of repeated glaciations. Thename pleistocene is derived from the Greek (pleistos"most") and (kainos "new").The Pleistocene epoch follows the Pliocene epochand is followed by the Holocene epoch. ThePleistocene is the third epoch of the Neogene periodor 6th epoch of the Cenozoic Era. The end of thePleistocene corresponds with the end of thePaleolithic age used in archaeology.The name was intended to cover the recent period ofrepeated glaciations; however, the start was set toolate and some early cooling and glaciation are nowreckoned to be in the Gelasian (end of the Pliocene).Some climatologists and geologists would thereforeprefer a start date of around 2.58 million years BP.The name Plio-Pleistocene has in the past been usedto mean the last ice age. But since only a part of thePliocene is involved, the Quaternary wassubsequently redefined to start 2.58 Ma. as moreconsistent with the data. The continuous climatichistory from the Pliocene into the Pleistocene andHolocene was one reason for the InternationalCommission on Stratigraphy to proposediscontinuance of the use of the term "Quaternary".The Pleistocene corresponds to this archeologicalperiod.The various times studied by a QuaternaryGeologist.Paleogeography and climateThe modern continents were essentially at theirpresent positions during the Pleistocene, the platesupon which they sit probably having moved no morethan 100 km relative to each other since thebeginning of the period.Number of inches continents move at most relativeto each other per year.Glacial featuresPleistocene climate was characterized by repeatedglacial cycles where continental glaciers pushed tothe 40th parallel in some places. It is estimated that,at maximum glacial extent, 30% of the Earth'ssurface was covered by ice. In addition, a zone ofpermafrost stretched southward from the edge of theglacial sheet, a few hundred kilometres in NorthAmerica, and several hundred in Eurasia. The meanannual temperature at the edge of the ice was 6C;at the edge of the permafrost, 0C.Each glacial advance tied up huge volumes of waterin continental ice sheets 15003000 m thick,resulting in temporary sea level drops of 100 m ormore over the entire surface of the Earth. Duringinterglacial times, such as at present, drownedcoastlines were common, mitigated by isostatic orother emergent motion of some regions.The effects of glaciation were global. Antarctica wasice-bound throughout the Pleistocene as well as thepreceding Pliocene. The Andes were covered in thesouth by the Patagonian ice cap. There were glaciersin New Zealand and Tasmania. The current decayingglaciers of Mount Kenya, Mount Kilimanjaro, andthe Ruwenzori Range in east and central Africa werelarger. Glaciers existed in the mountains of Ethiopiaand to the west in the Atlas mountains.and to the west in the Atlas mountains....
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Week3_Pleistocene - 3-1Week 3: Pleistocene EpochThe...

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