Did Dinosaurs Once Roam the Grand Canyon?

Dinosaurs may have once roamed near the Grand Canyon.

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(U.S. News Illustration/iStock)

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Tyrannosaurus Rex may have once hung out in the Grand Canyon.

A new study suggests the western portion of the canyon may be 70 million years old and may have been carved by an ancient river; previous estimates suggest the canyon is just 6 million years old.

Scientists from the University of Colorado took rock samples from the bottom of the western part of the canyon and, using a phosphate-based mineral known as apatite, were able to date the bottom of the western part of the canyon to 70 million years ago.

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The process is called thermochronometry and uses the thermal history of minerals taken from the bottom of the Grand Canyon compared with rocks that lie several miles beneath the Earth's surface.

"Rocks cool as they approach the Earth's surface by erosion, and [apatite] records this cooling history," the report says. "Data from the western Grand Canyon suggested excavation to within several hundred meters of the canyon's modern depth by [70 million years ago], in direct conflict with the young canyon model."

"All of it was already carved except for maybe 300 or 400 meters," Rebecca Flowers, coauthor of the report, which appears in the journal Science, says. "The results of our study imply the history of this canyon is more complicated than we previously thought."

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That means dinosaurs may have once roamed near the canyon; they didn't go extinct until about 65 million years ago, and the Tyrannosaurus Rex and Plesiosaurs were native to the region.

The predominant theory about the formation of the Grand Canyon is that the Colorado River, which flows southwest through the canyon, over the course of millions of years, carved the canyon. Flowers says her team's findings suggest that another river system was responsible for carving it.

"We think that the canyon was carved by a river, but it happened much longer ago, and it was flowing in a different direction than the Colorado River is flowing today," she says. "We think there was a river back then that actually flowed eastward from the western highlands. The landscape, tectonics, and drainage systems likely looked very different than it does today."

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Sometime over the last several million years, the Colorado River formed and began flowing through the canyon, she says.

Scientists have been unable to find fossils that suggest the canyon is as old as Flowers says it is, but she says that's a result of how canyons are formed.

"What's inherent with erosion is that you're removing material, taking stuff away," she says. "That's one of the challenges with this kind of work — you don't have a direct rock record of where that eroded stuff went, we don't have a fossil record."

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Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at jkoebler@usnews.com.