Pleistocene epoch


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Related to Pleistocene epoch: Pliocene epoch, Holocene epoch

See also: Geologic Timescale (table)Geologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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Pleistocene epoch

(plī`stəsēn), 6th epoch of the Cenozoic eraCenozoic era
, last major division of geologic time (see Geologic Timescale, table) lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the
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 of geologic time (see Geologic TimescaleGeologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
..... Click the link for more information.
, table). According to a classification that considered its deposits to have been formed by the biblical great flood, the epoch was originally called the Quaternary. Analyses of the magnetic polarity in deep-sea sediment cores indicated that the Pleistocene began more than 1.8 million years ago—much earlier than had previously been suspected (see glacial periodsglacial periods,
times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch, in the Carboniferous and Permian periods of the Paleozoic era era, and in Huronian time of the Precambrian, the earth experienced an
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). Since the interglacial periods of the Pleistocene were of longer duration than the time elapsed since the end of the Pleistocene 11,000 years ago, it is sometimes suggested that the Holocene, or Recent, epoch, which is occurring now, may be merely another such interglacial stage and that the glaciers may return at some future time.

An Ice Age

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.

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.

Topographic and Climatic Changes during the Pleistocene

The characteristic formation laid down in the glacial stages of the Pleistocene, as in all glacial periods, is the driftdrift,
deposit of mixed clay, gravel, sand, and boulders transported and laid down by glaciers. Stratified, or glaciofluvial, drift is carried by waters flowing from the melting ice of a glacier.
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. The interglacial stages were marked by the weathering of the till of the drift to form a sticky, heavy soil called the gumbotil and by the deposition of peat and loess. Peat is plentiful in the Aftonian, Yarmouth, and Sangamon interglacial stages in North America.

The Pleistocene glaciers made important alterations in the topography of the glaciated regions, leveling hilly sections to low, rolling plains, both by erosion and by deposition of drift, eroding hollows that later became lakes, and forcing rivers to cut new channels by filling their former beds. Among the characteristic surface features formed in the Pleistocene are the drumlindrumlin
, smooth oval hill of glacial drift, elongated in the direction of the movement of the ice that deposited it. Drumlins, which may be more than 150 ft (45 m) high and more than 1-2 mi (.8 km) long, are common in New York, Wisconsin, Canada, and Northern Ireland.
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, kamekame
, low, steep, rounded hill or ridge of layered sand and gravel drift, developed from glacial deposits. Kames were probably formed by streams of melting glacial ice that deposited mud and sand along the ice front.
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, eskeresker,
long, narrow, winding ridge of stratified sand-and-gravel drift. Eskers, many miles long and resembling abandoned railway embankments, occur in Scandinavia, Ireland, Scotland, and New England; they arose from deposition of sediment in the beds of streams flowing through
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, and morainemoraine
, a formation composed of unsorted and unbedded rock and soil debris called till, which was deposited by a glacier. The till that falls on the sides of a valley glacier from the bounding cliffs makes up lateral moraines, running parallel to the valley sides.
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. The retreat of the ice after the Wisconsin glacial stage was followed by the formation, at the edge of the melting glaciers, of lakes, such as the extinct Lake AgassizAgassiz, Lake
, glacial lake of the Pleistocene epoch, c.700 mi (1,130 km) long, 250 mi (400 km) wide, formed by the melting of the continental ice sheet beginning some 14,000 years ago; it eventually covered much of present-day NW Minnesota, NE North Dakota, S Manitoba, central
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 and the Great Lakes. The further retreat of the ice led to the flooding by the Atlantic of the NE United States and SE Canada, which had been depressed below sea level by the weight of the ice. In the areas of North America not covered by ice, the Pleistocene was marked chiefly by erosion, with only very slight marine transgressions over the coast.

During the various glacial stages many areas not covered with ice, including the arid and semiarid parts of the W United States, had periods of increased rainfall and lessened evaporation. Called pluvial periods, they were characterized by the spread of vegetation and the formation of many lakes. Heavy precipitation in the West was responsible for two great lakes—Lake Lahontan of Nevada and Lake Bonneville of Utah (which today forms the Great Salt and Utah lakes). During the Pleistocene, volcanic activity and warping of the earth's surface occurred on the Pacific coast. The cutting of the Grand Canyon took place chiefly in Pleistocene time.

Fauna of the Pleistocene

Among the characteristic Pleistocene mammals of North America were at least four species of elephants, including the mastodon and the mammoth, true horses, of the same genus as the domestic horse though not of the same species, saber-tooth carnivores, large wolves, giant armadillos and ground sloths, bisons, camels, and wild pigs. Among the arctic mammals that ranged far south in the glacial stages were the musk ox in North America and the woolly mammoth in Europe. The Pleistocene saw the beginning of the trend toward the extinction of many mammal species, which continued into historic times. The Pleistocene is noted also for the first appearance of modern humans approximately 500,000 years ago and the migration of humans to the American continents.

References in periodicals archive ?
At the end of the Pleistocene epoch, during the Wisconsinan glacial period, an enormous amount of the Earth's water supply was frozen in huge ice sheets--some up to two miles thick--leaving the sea 280 to 350 feet below today's level.
An international team deciphered the genome of the horse from the Middle Pleistocene epoch, along with those of a 43,000-year-old horse, a modern donkey and five contemporary domestic horse breeds.
Held at the National Library of the Kingdom of Morocco, this exhibition showcases the results of main joint projects under the Spanish-Moroccan cooperation protocol in Archaeology and Heritage signed in 1988, including those relating to human presence in the eastern part of Morocco during the Pleistocene epoch, the archaeological research in the regions of "Jbala-Ghomara" and "Souss Tekna", the archaeological map of northern Morocco, and the Neolithic origins in Mediterranean Morocco.
Researchers analyzed samples from 24 human bones and 48 animal fossils in the Florida Museum's collections and determined the specimens were all from the late Pleistocene epoch about 13,000 years ago.
The skeleton is up to 75 percent complete and is probably from the Pleistocene Epoch, said Assistant City Manager Hugh Riley.
During the Pleistocene Epoch, which ended about 11,000 years ago, this scavenger dined on the carcasses of mastodons, giant sloths, primitive horses, and other megafauna of the time.
Records of the period studied in this research work reveal a sharp increase in dust and iron inputs during the Climate Transition of the Middle Pleistocene Epoch (1,250,000 years ago) in which fluxes tripled.
It is a vast plain of sand dunes, the remnant of a 600-foot-deep lake that covered this desert floor in the Pleistocene Epoch.
The diprotodon lived during the Pleistocene Epoch, an era spanning 2.
By examining the rocky strata around the fossils, they dated them to the middle of the Pleistocene epoch, almost a half-million years ago.
The experts opine that at the end of the Pleistocene epoch, populations of most species experienced a significant loss of numbers.
Seafaring ancestors moved into freshwater lakes when the glaciers receded at the end of the Pleistocene epoch.