The Grand Canyon is dramatic enough today - but imagine it with roaming dinosaurs. It now appears that it's been around for 70 million years, a good 65 million longer than believed.
The claim is based on an analysis of mineral grains from the bottom of the western Grand Canyon, using a dating method based on the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite.
"Our research implies that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago," says University of Colorado Boulder assistant professor Rebecca Flowers.
There's a good deal of controversy among scientists over the age and evolution of the Grand Canyon. The most popular theory places the age of the Grand Canyon at five to six million years, based on the age of gravel washed downstream by the ancestral Colorado River. In contrast, a 2008 study of mineral deposits inside caves carved in the canyon walls put its age at around 17 million years.
In fact, says Flowers, it seems likely that it wasn't carved all at the same time. Different canyon segments may have evolved separately before coalescing into what we see today.
"If it were simple, I think we would have solved the problem a long time ago," she says. "But the variety of conflicting information has caused scientists to argue about the age of the Grand Canyon for more than 150 years. I expect that our interpretation that the Grand Canyon formed some 70 million years ago is going to generate a fair amount of controversy, and I hope it will motivate more research to help solve this problem."
Over a mile deep in places, Arizona's steeply-sided Grand Canyon is about 280 miles long and up to 18 miles wide in places. It was likely carved in large part by a predecessor of the Colorado River that actually flowed in the opposite direction millions of years ago, says Flowers.
"An ancient Grand Canyon has important implications for understanding the evolution of landscapes, topography, hydrology and tectonics in the western US and in mountain belts more generally," says Flowers.