But because farmlands are primarily on lowlands, the gigantic sediment influx to rivers — caused by simply clearing and plowing land and making soil more vulnerable to washing away — is now coming from places like the Great Plains of the North America. That difference has caused yet another change — the overall lowering of the Earth’s landmasses by some 2 1/2 inches.
That last number is not particularly scary, given the mean elevation of Earth's land masses is 2,750 feet above sea level, the researchers reported.
But given the possibility that it's the most productive soil that's being shifted away from croplands, and that the need for food will increase as the human population grows, "the impact is significant," they concluded.
"One of the big questions that (they) address is ‘How sustainable is this?’" said geologist Roger Hooke of the University of Maine at Orono. Hooke is among many scientists who have been pondering the human contribution to erosion for many years.
That said, the biggest contribution of the new study, he said, is that it adds the perspective of Earth's sedimentation rates long before humans showed up. That provides a basis for comparison that hadn't been part of the puzzle until now.
