Washington Post: The Grand Canyon is generally believed to be only 6 million years old. A new study using a technique called thermochronology claims the accepted age is off by an order of magnitude. Thermochronology determines the history of rocks based on their phosphate crystals. The crystals, known as apatite, can trap the helium created by the decay of uranium and thorium. If there is helium in the crystal, then the crystals were formed near the surface. By collecting samples from multiple sites and levels, scientists can determine how long ago the crystals in the rocks formed. Rebecca Flowers of the University of Colorado believes that the thermochronology data her team has collected puts the age of the canyon at 70 million years, and that the canyon was cut in multiple stages. The 70-million-year-old western section was carved by a river flowing opposite the direction of the current Colorado River, And the eastern section would have been carved by a second river 55 million years ago. The Colorado joined the two sections 6 million years ago. Flowers’s theory is facing stiff resistance from other geologists who believe that she is misinterpreting the data she has collected and that the evidence for the 6-million-year-old age is overwhelming.