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What Started the Ice Age?
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# : |
16700 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
10 / 1989 |
2,979 Words |
| Author
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Marc J. Defant
Marc J. Defant is professor of geology at the University of
South Florida. He specializes in the study of volcanoes and is
the author of Voyage of Discovery: From the Big Bang to the
Ice Ages, a panoramic history of the universe, including our
galaxy, solar system, and planet. |
Woolly mammoths preserved by conditions during the last glacial era have long been surrounded in legend. Their ivory, particularly from the frozen wastelands of Siberia, is considered sacred and has been a commodity of trade throughout the world. Folklore even has it that many people throughout the centuries have tried to feast on preserved mammoth meat.
The intrigue surrounding preserved mammoths is merely part of man's deeper fascination with the glacial age and its mysteries. Since the realization that such glacial periods have occurred regularly in the past, scientists have tried to discover their cause. Evidence has mounted that glacial ages result from periodic changes in the way the earth orbits the sun. In addition, recent data suggest that the Ice Age began around 2.5 million years ago due to the uplift of two large plateaus on nearly opposite sides of the earth.
A Unique Time on Earth
Geologists know that the earth's climate has been colder than it is today at many times in the past because evidence of extensive glaciation exists in the geologic record. Both the woolly mammoth and the Alaskan steppe bison were frozen during the time of the last Neanderthals in Europe, when both Eurasia and North America were in the throes of the Ice Age. However, the ice receded during a warming trend that began approximately 17,000 years ago, so that by 7,000 years ago the glaciers had retreated to their present positions.
Massive ice sheets have advanced and retreated dozens of times during the last 2.5 million years. Many scientists believe that the earth is currently enjoying a warm interglacial period and will enter a new glacial epoch within the next 50,000 years.
At one point during the glacial epochs, immense continental glaciers covered nearly 11 million square miles of land that are free of ice today. They were more than a mile thick and in North America extended as far south as northern Kentucky. In Europe, the glaciers reached into parts of northern Germany and the Soviet Union and covered almost all of Great Britain and Denmark. The glaciers scoured the five Great Lakes and the Finger Lakes in New York, formed Long Island by depositing material as they moved into the Atlantic Ocean, and gouged out Minnesota's "10,000 lakes." As the glaciers grew by accumulating water from the oceans, the sea level dropped by 350 feet, exposing vast expanses of the continental shelves. The land bridges formed during this time allowed Stone
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