March 8, 2008--The Grand Canyon is much, much older (LA Times)
The Grand Canyon is as much as three times as old as geologists had previously believed, at least 17 million years old, researchers reported Friday in the journal Science. Scientists previously believed it to be about 5 million to 6 million years old, but dating it has proved difficult because erosion on the sides of the canyon has destroyed much evidence of its antiquity. A team from the University of New Mexico used new dating techniques to estimate the age of "mammillaries," thick white and yellowish-orange calcite deposits in caves along the walls of the canyon, where they are protected from erosion. The mammillaries mark the height of river water when they were formed. The evidence suggests that the eastern end was produced by a different river that began its erosive process much later. When the two rivers joined up about 5 million to 6 million years ago to form the Colorado River, the erosion accelerated dramatically, to a rate of about 8 to 12 inches every thousand years.
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