Earth Movers: Humans Cause Most Erosion

Human activity causes 10 times more soil erosion than all natural processes combined, according to a new study. And it's been that way for a long time.

People have been the main cause of erosion on continental surfaces since early in the first millennium, says Bruce Wilkinson, University of Michigan geologist.

Wilkinson used existing figures natural erosion amounts to about 60 feet every 1 million years.

In agricultural regions of the United States, the rate runs around 1,500 feet per million years, due largely to the human touch. Rates are even higher in other parts of the world, he said today.

The scientist then calculated a global average rate for human effects.

"We move about 10 times as much sediment as all natural processes put together," he said.

Here's why this is important: Earth's surface involves a balanced process, whereby new soil forms at about the same rate as it erodes. If humans are stripping soil at the rate Wilkinson calculates, Nature won't be able to keep up.

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

Wilkinson will present his findings Nov. 8 at a meeting of the Geological Society of America in Denver, Colo.