Sunday, March 09, 2008

New debate over the age of the Grand Canyon

A paper in Science this week by Polyak et al, asserts that the Grand Canyon started forming 17 million years ago. It’s been picked up by the popular press and appeared widely in newspapers.

But AZGS geologists reaffirm the evidence that shows the Canyon is only about 4.8 - 5.6 million years old. Jon Spencer and Phil Pearthree of AZGS and Kyle House of the Nevada Bureau of Mines and Geology examined the Science article and take exception with the interpretation of speleothems in caves far apart and away from the river being evidence that water table declines indicate time of canyon incision. Our team argues that a proto-canyon would have had to develop and propagate far upstream (perhaps 100 km or more) geologically instantaneously for this to happen.

Instead, our team notes the water table decline coincides with initiation of Basin and Range faulting 16-17 mya and is more likely the result of related subsidence. [photo: Alex Tostado Photography]

Ref: Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table-Type Speleothems, Victor Polyak, Carol Hill, and Yemane Asmerom (7 March 2008) Science 319 (5868), 1377. [DOI: 10.1126/science.1151248]

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