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Ice Ages, periods in Earth’s history when sea ice or glaciers have covered a significant portion of the planet’s surface and significant cooling of the atmosphere has occurred. Earth has existed for about 4.5 billion years. During that time it has experienced several ice ages, each lasting tens of millions of years. The total of these episodes may account for as much as 15 to 20 percent of the planet’s history. The icy cover has ranged from about 10 percent to about 30 percent of the entire surface of the planet.
The most recent ice age, the Pleistocene Epoch, lasted from about 1.6 million years to 10,000 years before present. During that time at least 20 glaciations, or periods when the ice cover increased, occurred. Each of these periods was followed by an interglaciation, or a period when the ice cover shrank. The most recent glaciation in North America, called the Wisconsin glaciation, lasted from about 115,000 years ago to 10,000 years ago. The climate during that time was much different from what it is today, with temperatures on the continents as much as 15° C (27° F) colder. In areas that are currently occupied by subtropical deserts, cooler and wetter climates caused large lakes to form from increased rainfall and glacial runoff. The past 10,000 years have been part of a relatively warm interglacial period. However, the presence of massive continental ice sheets on Greenland and Antarctica, along with numerous smaller glaciers in mountainous regions throughout the world, indicates that Earth is still in the grip of an ice age.
Benn, Douglas I., with David J. A. Evans. Glaciers and Glaciation. Wiley, 1998. For readers who wish to know the current state of the field and its preoccupations.
Bennett, Matthew R. and Neil F. Glasser. Glacial Geology: Ice Sheets and Landforms. Wiley, 1996. Provides a comprehensive and informative summary of modern glacial geology.
Gordon, John Ewart. Glaciers. Voyageur Press, 2001. Excellent illustrated introduction to glaciers. For middle-school readers.
Molnia, Bruce. Alaska's Glaciers. Rev. ed. Alaska Geographic Society, 1993, 2001. A spectacular book for the arm-chair enthusiast.
Post, Austin, and Edward R. LaChapelle. Glacier Ice. Rev. ed. University of Toronto Press, 2000. Informative text and beautiful photographs capture the awesome majesty of glaciers.
Bonnichsen, Robson, and others, ed. Ice Age Peoples of North America. Oregon State University Press, 1999. A collection of essays regarding the origins of indigenous North Americans.
Gershenson, Bernard. Between Ice Ages. Heyeck, 1997. A look at life on earth between the ice ages.
Imbrie, John, and Katherine Palmer Imbrie. Ice Ages: Solving the Mystery. Harvard University Press, 1986. Describes the processes that drive ice ages.
Pielou, E. C. After the Ice Age: The Return of Life to Glaciated North America. University of Chicago Press, 1991, 1992. Examines the transformation of the land after extended periods of glaciation.
Stanley, Steven M. Children of the Ice Age: How a Global Catastrophe Allowed Humans to Evolve. Harmony, 1996. Reprint, W. H. Freeman, 1998. Critiques the competing theories of evolution and offers fresh insights.
Goldstein, Barry, B.S., M.S., Ph.D. Professor, Department of Geology, University of Puget Sound.
Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation.
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