Overall view from the south Rim of the Grand Canyon near Tusayan, Arizona August 10, 2012. (Photo : Reuters)
A new study claiming the Grand Canyon is ten times older than previously thought is causing controversy among the ranks of geologists who specialize in the history of the canyon.
Rebecca M. Flowers of the University of Colorado and Kenneth A. Farley of the California Institute of Technology say new techniques for dating eroded rocks show that rivers had already dug out much of the canyon 60 million years ago, a time so long ago that dinosaurs still roamed the earth.
The currently accepted age of the Grand Canyon is 6 million years, still ancient, but long after the last dinosaurs died out and around the time our first human-like ancestors began to evolve.
"Our data detects a major canyon sitting there about 70 million years ago," said Flowers, whose paper was published in the journal Science on Thursday. "We know it's going to be controversial."
The Flowers study employs a technique called thermochronology, which focuses on concentrations of a mineral called apatite that decays in different ways depending on its surroundings.
When submerged in the heat far beneath the surface of the earth, radioactive isotopes in the apatite decay without producing helium. But if the mineral is exposed on the surface and subjected to cooler temperatures, the uranium and thorium is contains decay into helium.
Flowers speculates that the western part of the canyon formed first, before the eastern part of the canyon formed separately, carved by different and now non-existent rivers. Then, much later, the Colorado River, which currently cuts through the entire Grand Canyon, connected the two canyon systems.
Thermochronology allows much more specificity in determining the history of particular rocks. While scientists who support the more traditional "young canyon" view don't dispute the science, they do contend that Flowers' interpretation of her results ignores other evidence that points to a more recent origin.
"It is simply ludicrous," said Karl Karlstrom, professor of geology at the University of New Mexico.
"Rugged topography like that fills in with erosion in way less than a million years."
Karlstrom says he is excited about the potential of thermochronology. "Less welcome to me," he said, "is their attempt to push the interpretation of their new data to their limits without consideration of the whole range of other geologic data sets."