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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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ScienceShot: Erosion in Flatland
1 February 2013 12:05 pm
Who says Earth's not flat? Even though more than half of the planet's ice-free terrain has a slope of 0.6° or less, where water flow is generally languid, a significant part of the world's erosion takes place there, a new study reveals. By analyzing river sediments collected at thousands of locations worldwide and estimating their concentration of the isotope beryllium-10 (which is produced when cosmic rays strike rocks at or near Earth's surface), researchers could assess rates of erosion in those watersheds. For watersheds with areas ranging between 1 and 10,000 square kilometers, rates of erosion were strongly correlated with the average steepness of the watershed when that slope exceeded 11.3° (a rise of 200 meters for every horizontal kilometer). Rates of erosion were less predictable in more gently sloping landscapes, but data suggest that the breakdown of rocks in ice-free terrain creates about 5.5 billion tons of sediment worldwide each year, the researchers report in a forthcoming issue of Geology. Although erosion can remove as much as 6 meters of material in mountainous areas (such as in the Grand Tetons in the above background) each millennium, in gently sloping areas (foreground) wind and water may strip away as little as 0.5 millimeters per year. Overall, at least half Earth's surface loses about 12 millimeters or more to erosion every 1000 years, the team estimates. Altogether, about 80% of the world's sediment is produced by erosion of terrain with a slope of 6° or less.
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