Analysis of minerals from the bottom of the western Grand Canyon in Arizona indicates it was largely carved out by about 70 million years ago, they said.
That pushes back the conventionally accepted date for the formation of the Grand Canyon in Arizona by more than 60 million years, CU-Boulder Professor Rebecca Flowers said.
That means the canyon was carved to near its current depth during the time of the dinosaurs, which may have even peeked over its rim, the researchers said.
The age of Arizona's Grand Canyon, about 280 miles long and up to 18 miles wide in places, has been the subject of considerable controversy among scientists.
The most popular theory places the age of the Grand Canyon at 5 million to 6 million years based on the age of gravel washed downstream by the ancestral Colorado River.
However, a 2008 study estimated the Grand Canyon to be some 17 million years old after researchers dated mineral deposits inside of caves carved in the canyon walls.
Flowers' team arrived at their estimate using a dating method that exploits the radioactive decay of uranium and thorium atoms in a phosphate mineral known as apatite at the bottom of the canyon, a university release 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," Flowers said.