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How Old Is the Grand Canyon?
mongabay.com
March 6, 2008
The Grand Canyon began to open at least 17 million years ago — older than previously believed — report researchers writing in the journal Science.
Using uranium-lead isotope dating to determine the age of carbonate deposits that form in the canyon's caves, Victor Polyak and colleagues found that the "canyon is oldest on its western end and opened up steadily to the east through headward erosion". They estimate that the canyon was completely cut through 5 to 6 million years ago — the age previously cited for when the canyon began to form.
The researchers described their methodology as follows:
"For the Grand Canyon area, there is no better niche than caves to find both clastic and chemical sediments that were deposited before, during, and after the incision of the canyon," write the authors. "Equally important, these cave deposits are located throughout the canyon. Caves are not only well suited to contain these deposits, they also provide an ideal environment that preserves and protects them from weathering."
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The Grand Canyon. Photos by R. Butler
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"These mammillary coatings in the Grand Canyon caves contain sufficient uranium-lead ratios and yield U-Pb dates that place the water table within the canyon at a particular place and at an absolute time. This allows for the incision history of the Grand Canyon to be reconstructed on the basis of the premise that the timing of this water table descent is coeval with incision of the Colorado Plateau by the Colorado River system."
In a related article Tim Atkinson and Michael Leeder say that while the dating is consistent with previous estimates, the methodology "places the dates on a firm footing for the first time."
The Grand Canyon is 277 miles long, 1.1 miles deep at its deepest point and up to 18 miles wide.
V. Polyak and C. Hill (2008). Age and Evolution of Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleothems. Science 07 March 2008.
T.C. Atkinson and M. Leeder (2008). Canyon Cutting on a Grand Time Scale. Science 07 March 2008
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