Technical Comments

Response to Comments on the "Age and Evolution of the Grand Canyon Revealed by U-Pb Dating of Water Table–Type Speleothems"

Science  19 Sep 2008:
Vol. 321, Issue 5896, pp. 1634
DOI: 10.1126/science.1159762

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Pederson et al. and Pearthree et al. offer critical comments on our study of the age and evolution of the Grand Canyon. Both sets of authors question our use of incision rates from two sample sites located outside the canyon and present alternative interpretations of our data. As we explain, even without the sites in question, our data support a “precursor” western Grand Canyon older than 6 million years.

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