for National Geographic News
In a week when massive flooding (see photo) is turning back the clock a bit for the Grand Canyon, a controversial new study is shedding light on just how far back the canyon's history goes.
The vast gorge may have been formed millions of years earlier than thought, the report says. The findings fly in the face of long-standing theory.
The traditional view is that the massive gorge is a uniform six million years old, and that the Colorado River is almost entirely responsible for carving the Arizona canyon.
But the new study says the western reaches of the Grand Canyon began forming 17 million years ago, thanks to slow erosion that started before the river existed.
The researchers also found that the eastern half formed within the past four million years—not six million—as the river cut into the Colorado Plateau.
The scientists based their research on clues tucked within caves in canyon walls.
Compiled by lead author Victor Polyak and colleagues at the University of New Mexico, the results will appear in tomorrow's issue of the journal Science—and they will likely be hotly contested, experts say.
(See photos of the Grand Canyon.)
Until now, efforts to describe the Grand Canyon's formation relied on geologic events such as rock flows and deposits of sedimentary rock.
But those records are only reliable to about a million years ago, the authors write.
So Polyak and his colleagues reasoned that as water cut down into northern Arizona's rock layers—forming the canyon walls—the surrounding water table dropped alongside it.
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