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Pleistocene
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The Pleistocene is the best-known glacial period (Ice Age) of the earth’s history. Its ice sheets at one time covered all of Antarctica, large parts of Europe, North America, and South America, and small areas in Asia. In North America they stretched over Greenland and Canada and over the United States as far south as a line drawn westward from Cape Cod through Long Island, New Jersey, and Pennsylvania, along the line of the Ohio and Missouri rivers to North Dakota, and through N Montana, Idaho, and Washington to the Pacific. The ice sheets of Europe radiated from Scandinavia and covered Finland, NW Russia, N Germany, and the British Isles. Glaciers distinct from the main sheets were formed in the Rockies and the Alps. In South America, Patagonia and the S Andes lay under an extension of the antarctic sheet, while in Asia the Caucasus, the Himalayas, and other mountain regions were glaciated.
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Before the Pleistocene glaciation, Ohio was much different than today. Lake Erie did not exist and a major river, the Erigans River, flowed in a wide valley where the lake is today. Much of Ohio was drained by an ancient river, known as the Teays, that had headwaters in NorthCarolina and flowed northward across Virginia and West Virgina, entering Ohio near Portsmouth. The Teays River then flowed northward to Chillicothe then westward across western Ohio, Indiana, Illinois, and into the ancestral Mississippi River. The Ohio River did not exist at this time. Some geologists speculate that the Teays flowed northward from Chillicothe and joined the Erigans River.
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In recent years, the view that Pleistocene climatic events played a major role in the evolution of the biotas of southern, primarily tropical continents has begun to displace the previously held conviction that these areas remained relatively stable during the Quaternary. Studies of speciation patterns of high Andean plant and avian taxa (7-14) have led to the conclusion that Pleistocene climatic events were the factors that ultimately shaped the patterns now observed in the paramo-puna and the related Patagonian flora and fauna. The final uplift of the Andes at the end of the Tertiary automatically limits the age of the high Andean habitats and their biotas to the Quaternary. Within this period, the number of ecological fluctuations caused by the glaciations could easily have provided the mechanism behind the patterns now present in these habitats (Appendix, 1; Figs. 1 and 2; Table 1). In glacial periods, when vegetation belts, were lowered, organisms in the paramo-puna habitat were allowed to expand their ranges.
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Other clues about the climate of the Pleistocene are trapped in the ice of Antarctica and the Arctic region. During glacial stages, seawater froze into huge glaciers, lowering the level of the oceans. Sea level dropped by as much as 150 m (490 ft), as water from the oceans froze into glaciers and ice sheets. The continental shelves, or the edges of a continent that extend out into the ocean, became dry land as the ocean levels dropped. The newly uncovered land quickly dried and added dust to the atmosphere. Some of the dust settled in the Arctic and Antarctic regions, where new layers of ice covered and trapped it.
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An ooid sand barrier bar of Pleistocene age was deposited along the seaward side of an ooid shoal complex southwest of Miami, Florida. The bar is 35 km long, about 0.8 km wide, elongate parallel with the trend of the ooid shoal complex and perpendicular to channels between individual shoals. A depression 1.6 km wide, interpreted as a back-barrier channel, isolates the bar from the ooid shoals. During sea-level fall and subaerial exposure of the bar, the ooid sand was cemented in place, preventing migration of the barrier. No Holocene analogue of this sand body is recognized, perhaps because of the relative youthfulness of Holocene ooid shoals. This Pleistocene ooid shoal complex, with its reservoir-size barrier bar, may serve as a refined model for exploration in ancient ooid sand belts.
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The glaciation of the Pleistocene was not continuous but consisted of several glacial advances interrupted by interglacial stages, during which the ice retreated and a comparatively mild climate prevailed. In all probability there were actually only four glacial stages, the Iowan and Bradyan being included in the Wisconsin as one complex stage. Carbon-14 analysis of fossils shows that the last glacial period ended about 11,000 years ago.
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Pleistocene