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Updated 11:00 AM November 1, 2004




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Here's the dirt: People cause more erosion than natural processes

Human activity causes 10 times more erosion of continental surfaces than all natural processes combined, an analysis by a U-M geologist shows.

Moreover, people have been the main cause of worldwide erosion since early in the first millennium, says Bruce Wilkinson, a professor of geological sciences. Wilkinson will present his findings Nov. 8 at a meeting of the Geological Society of America in Denver.

Many researchers have tried to assess the impact of human activity on soil loss, but most have only guessed at how erosion due to natural forces such as glaciers and rivers compares with that caused by human activity—mainly agriculture and construction, Wilkinson says. He used existing data on sedimentary rock distributions and abundances to calculate rates of natural erosion.

"If you ask how fast erosion takes place over geologic time—say over the last 500 million years—on average, you get about 60 feet every million years," Wilkinson says.

In those parts of the United States where soil is being eroded by human agricultural activity, however, the rate averages about 1,500 feet per million years, and rates are even higher in other parts of the world.

Natural processes operate over areas larger than those affected by agriculture and construction, but even taking that into account, he says, "the bottom line is, we move about 10 times as much sediment as all natural processes put together."

Because soil formation proceeds at about the same rate as natural erosion, Wilkinson's results mean that humans are stripping soil from the surface of the Earth far faster than nature can replace it.

"This situation is particularly critical," Wilkinson says, "because the Earth's human population is growing rapidly, and because almost all potentially arable land is now under the plow."

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