Researchers discover the true age of the Grand Canyon through information hidden inside.

by Steve Carr

Up until recently, it was thought the Grand Canyon was approximately six million years old. Researchers in the Earth and Planetary Sciences at the University of New Mexico have recently contradicted this and discovered otherwise.

Using a technique called uranium-lead isotope (U-Pb) dating of water table-type speleothems or cave formations, researchers Victor Polyak, Carol Hill, and Yemane Asmerom, were able to determine the western portion of the Grand Canyon actually began to form some 17 million years ago.

That revelation, or “eureka moment” as Asmerom calls it, essentially proves the Grand Canyon to be three times older than originally thought.

The research, which began more than nine years ago, is funded by a grant from the National Science Foundation for $250,000 and was published recently in the journal Science. The discovery was enabled by the realization that certain cave formations, such as mammillary coatings that form near groundwater tables, provided the opportunity for researchers to date both parts of the canyon radiometrically accurately for the first time.

“The fact that many Grand Canyon caves contain mammillary speleothems has allowed us to take advantage of advances in U-Pb and U-series analytical techniques in an effort to make the long sought chronology possible,” says Polyak.

As it turned out, the caves and cave deposits, which are located throughout the Grand Canyon, were ideal in that the researchers found both pre-existing and chemical sediments deposited before, during, and after the incision of the canyon.

Naturally, the caves preserved and protected the deposits from weathering. With sufficient uranium lead ratios and yield U-Pb dates, the mammillary coatings place the water table within the canyon at a particular place and at an absolute time. The mammillary coatings allow for the incision history of the Grand Canyon to be reconstructed.

“We knew if we could successfully determine the age of these coatings, we could position a pre-existing water table at a certain place in the canyon at a particular time,” says Polyak.

The core data, which included 57 analyses, came from nine mammillary coatings from throughout the canyon, both east and west. The results from the eastern Grand Canyon displayed faster water table descent rates than data from the western Grand Canyon which showed stable, slow drops in the water table. The data showed a slower incision rate in the western portion than the eastern.

The resulting data provided a record of water table deposits as the Colorado River cut through the canyon over millions and millions of years – approximately 17 million for the western portion.

“Based on uranium-lead dates of these deposits and the positions of these deposits throughout the canyon, that the western Grand Canyon is much older than what most scientists have thought,” says Polyak.

“Normally what you’d expect is for the area around the headwaters to be older than what they call the ‘tail of the river,’ explains Asmerom. “Here, essentially, you have a 10 million year old pre-history of the western Grand Canyon before the Colorado River became a though-flowing river to the Gulf of California.”

The research may provide further information that could eventually offer the possible reconstruction of the canyon’s history.

“These results were achievable by the convergence of new technical capabilities achieved in our Radiogenic Isotope Laboratory, the conceptual breakthrough in connecting the mammillary to the water table and having samples that had sufficient uranium for dating,” says Asmerom.

For more information on the Radiogenic Isotope Laboratory at UNM visit: http://asmerom.unm.edu.

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