glacial periods definition of glacial periods in the Free Online Encyclopedia.

glacial periods, times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch Pleistocene epoch , 6th epoch of the Cenozoic era of geologic time (see Geologic Timescale, 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.
..... Click the link for more information. , in the Carboniferous Carboniferous period , fifth period of the Paleozoic era of geologic time (see Geologic Timescale, table), from 350 to 290 million years ago. Historical Geology of the Period

..... Click the link for more information. and Permian Permian period [from Perm, Russia], sixth and last period of the Paleozoic era (see Geologic Timescale, table) from 250 to 290 million years ago. Historical Geology of the Period
The Lower Permian

..... Click the link for more information. periods of the Paleozoic era Paleozoic era , a major division (era) of geologic time (see Geologic Timescale, table) occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (see each listed
..... Click the link for more information. era, and in Huronian time of the Precambrian era Precambrian era, name of a major division of geologic time (see Geologic Timescale, table), from c.5 billion to 570 million years ago. It is often divided into the Archeozoic and Proterozoic; in other countries, the Precambrian is broken into other divisions,
..... Click the link for more information. , the earth experienced an overall cooling of the climate, resulting in great ice sheets covering great portions of the oceans and continents continent, largest unit of landmasses on the earth. The continents include Eurasia (conventionally regarded as two continents, Europe and Asia), Africa, North America, South America, Australia, and Antarctica.
..... Click the link for more information. . More or less extensive continental glaciations, or glacial advances, may have occurred at other times. The study of glacial periods owed its first impetus to the Swiss-American naturalist Louis Agassiz, whose conception of Pleistocene glaciation was presented in his address before the Helvetic Society (1837) and in his Études sur les glaciers (1840). No satisfactory theory on the cause of glacial periods has yet been accepted. The earliest conception was that the earth's history has been one of progressive cooling, resulting in a major glaciation during the Pleistocene epoch. This concept lost its validity when the existence of earlier glacial periods, after which the earth again became warm, was established. In the mid-1800s, the Scot James Croll, an amateur scientist who later became a Fellow of the Royal Society, realized that the earth's heat balance could change as its orbit alters, thus accounting for the ice ages over time. Milutin Milankovitch, a Serbian mathematician, between World War I and II believed that ice ages occurred because of solar radiation fluctuations due to periodic changes in the earth's axis tilt and in its orbit. Other possible explanations for glacial advances include the changes in the direction of ocean currents, shifting of the continents over the earth's surface, fluctuation in the sun's energy and size, and loss of heat from the earth's surface through reduction of the carbon dioxide content of the atmosphere. One more recent theory postulates that large volcanic eruptions contribute to the short-term cooling of the globe and could increase their effects if many erupted over longer periods of time. One link between volcanoes and climate may be the Little Ice Age (1645–1715), when volcanic activity increased and worldwide temperatures decreased dramatically. Another theory states that dust thrown into the atmosphere by large asteroidal strikes would decrease solar radiation enough to cause global cooling; such a scenario has been invoked to explain the mass extinction mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events.
..... Click the link for more information. that occurred at the end of the Cretaceous period Cretaceous period , third and last period of the Mesozoic era of geologic time (see Geologic Timescale, table), lasting from approximately 144 to 65 million years ago.
..... Click the link for more information. .

Bibliography

See R. F. Flint, Glacial and Quaternary Geology (1971); R. P. Sharp, Living Ice: Understanding Glaciers and Glaciation (1991).

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No references found			The scientific celebrities, forgetting their mollusks and glacial periods, gossiped about art, while devoting themselves to oysters and ices with characteristic energy; the young musician, who was charming the city like a second Orpheus, talked horses; and the specimen of the British nobility present happened to be the most ordinary man of the party. Little Women by Alcott, Louisa May View in context			glacial advance glacial anticyclone glacial boulder Glacial Complex glacial deposit Glacial Deposits Glacial Dome glacial drift glacial epoch glacial erosion glacial flour glacial flow glacial geology glacial high glacial ice Glacial Isostacy glacial lake Glacial Lakes State Park Glacial Lithogenesis glacial lobe glacial maximum glacial mill Glacial Morphosculpture glacial outwash glacial period glacial periods glacial plucking Glacial Relicts glacial retreat glacial scour glacial striae Glacial Striation Glacial Theory glacial till glacial trough glacial varve glaciated terrain Glaciation glaciation limit glacier Glacier Bay Glacier Bay National Park & Preserve Glacier Bay National Park and Preserve Glacier County glacier flow glacier front glacier ice glacier mill Glacier National Park glacier pothole glacier table			Glacial Geology and Geomorphology Glacial Groove Glacial Groove Glacial Grooves Glacial Grooves Glacial Habitat Restoration Area glacial high Glacial horn glacial ice Glacial Isostacy Glacial lake Glacial lake outburst flood Glacial lakes Glacial Lakes Area Development Glacial Lakes Corn Processors Glacial Lakes Motorcycle Club Glacial Lakes State Park Glacial Lithogenesis glacial lobe Glacial maximum Glacial maximum glacial mill Glacial moraine Glacial moraine Glacial moraines Glacial moraines Glacial Morphosculpture Glacial outwash glacial period glacial period glacial periods Glacial phenol Glacial phosphoric acid Glacial plucking Glacial refugia Glacial refugia Glacial Relicts Glacial retreat Glacial Retreat in Antarctica and Deglaciation of the Earth System glacial scour Glacial sheet Glacial sheet Glacial Stage Glacial Stage glacial striae Glacial striation Glacial striation Glacial striations Glacial striations Glacial theory Glacial theory Glacial till Glacial till Glacial till Glacial till Glacial till plain Glacial till plains Glacial till plains Glacial till plains Glacial till plains glacial trough