for National Geographic News
New research on the Grand Canyon challenges the long-held belief that the canyon was carved by the mighty Colorado River about six million years ago.
Parts of the canyon were formed more than 50 million years earlier than previously thought, according to the new study.
The newfound evidence, which will be presented in the May issue of the Geological Society of America Bulletin, shows that part of the canyon known as Upper Granite Gorge formed more than 55 million years ago.
The history of the Grand Canyon is far more complicated than previously believed, according to Rebecca Flowers, a professor at the University of Colorado, Boulder and the paper's lead author.
"What this tells us is that the entire Grand Canyon didn't suddenly just form six million years ago," Flowers said.
Instead, she explained, the giant chasm may have formed as a series of "ancestral" canyons grew and joined together.
"It is becoming increasingly apparent that the history is more complicated and that different segments developed at different times and subsequently became integrated."
Canyon's Deep Debate
Scientists have long argued over how the Grand Canyon, arguably one of the best known and most beautiful landscapes on Earth, was formed. (See photos of the Grand Canyon.)
The most widely held belief was that it was created when geological forces lifted the area and the Colorado River cut down through the resulting plateau.
The canyon's age had been pegged at about six million years based on sediment deposited by the Colorado as it exited the canyon around Lake Mead (see a downloadable map of the Grand Canyon).
The new study used a different technique, a method of dating rocks developed by geologists at the California Institute of Technology called uranium-thorium-helium dating.
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