The western Grand Canyon was largely carved out by about 70 million years ago when dinosaurs roamed the earth, an analysis of mineral grains lying at the bottom of these hulking shapes reveals.
The new research pushes back the conventionally accepted date for the formation of the Grand Canyon in Arizona by more than 60 million years, says Rebecca Flowers, assistant professor of geological sciences at the University of Colorado Boulder.
The team used a dating method that exploits the radioactive decay of uranium and thorium atoms to helium atoms in a phosphate mineral known as apatite, said Flowers, who co-authored the study with Kenneth Farley, professor at the California Institute of Technology, the journal Science reports.
The helium atoms were locked in the mineral grains as they cooled and moved closer to the surface during the carving of the Grand Canyon, she said, according to a Colorado statement.
Temperature variations at shallow levels beneath the Earth's surface are influenced by topography, and the thermal history recorded by the apatite grains allowed the team to infer how much time had passed since there was significant natural excavation of the Grand Canyon, Flowers said.
"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," said Flowers.
Flowers said the entire modern canyon may not have been carved all at the same time. Different canyon segments may have evolved separately before coalescing into what visitors see today.
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.
Visited by more than five million people annually, the iconic canyon was likely carved in large part by an ancestral waterway of the Colorado River that was flowing in the opposite direction millions of years ago, said Flowers.
"An ancient Grand Canyon has important implications for understanding the evolution of landscapes, topography, hydrology and tectonics in the western U.S. and in mountain belts more generally," said Flowers.