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PERMAFROST Permafrost exists in climates in which the average temperature is below freezing. An estimated twenty percent of the earth's surface is permafrost; in northern Siberia, the world's oldest permafrost is 5,000 feet deep. Each year the layer thickens, reaching ever more deeply into the earth's crust. As seen in this aerial photograph, permafrost can cause grid-like frost heaves in the tundra. Scientists like Bill Fitzhugh and Sven Haakanson prize permafrost for its ability to preserve animal carcasses intact for thousands of years. |
