The Grand Canyon might be three times older than previously thought, the Washington Post reports. A study in Science claims that a river—not the Colorado, but a smaller one—began carving the oldest part of the canyon 17 million years ago. It contends that the canyon-building greatly accelerated 5 or 6 million years ago, which is why most geologists use that time frame as its age.
The researchers reached their conclusions by using uranium half-life dating on the canyon’s mammillaries, large rounded rocks that form near the top of a water table. Skeptics disagree. One expert says the older theory is not backed up by evidence in the form of sediment. "They clearly have not taken the time to be rigorous and actually understand the regional geography," he said.