Science  30 Nov 2012:
Vol. 338, Issue 6111, pp. 1134
  1. A Grand Old Canyon

    Parts of Arizona's Grand Canyon may be millions of years older than previously thought, suggests a study of helium atoms in mineral samples from the western reaches of the canyon.


    Helium, formed in minerals called apatites as a result of radioactive decay of uranium, diffuses through the mineral's crystal structure at deep underground temperatures above 70°C. But as the minerals rise toward Earth's surface—or as erosion carves a canyon toward the minerals—the rocks surrounding them cool, trapping more of the helium within the apatite grains. Helium concentrations in apatite can, therefore, serve as a geological time clock.

    The new study finds that much of the western portion of the Grand Canyon was carved to within a few hundred meters of its current depth by about 70 million years ago, scientists reported online this week in Science. That age is a far cry from the 5 to 6 million years previous researchers estimated by identifying when sediment from eastern portions of the canyon first appeared at the western end of the gorge.

Log in to view full text

Log in through your institution

Log in through your institution