Human activity causes 10 times more erosion of continental surfaces than all natural processes combined, an analysis by a University of Michigan geologist shows. [...]

"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 said. In those parts of the United States where soil is being eroded by human agricultural activity, however, the rate averages around 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, "the bottom line is, we move about 10 times as much sediment as all natural processes put together," he said.

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 said, "because the Earth's human population is growing rapidly and because almost all potentially arable land is now under the plow."

Here is the USDA's fact sheet on erosion.