Most previous estimates have put The Grand Canyon's age at 5 million to 6 million years, based on the age of gravel washed downstream by the ancestral Colorado River.
However, researchers say it was carved some 70 million years ago - at a time when dinosaurs still roamed the Earth, the 'Daily Mail' reported.
The study led by professor Rebecca Flowers from the University of Colorado Boulder, which used radioactive decay and thermal dating to make their estimate, found it is much older.
Flowers explained how the study exploited the radioactive decay of uranium and thorium atoms into helium atoms in a phosphate mineral known as apatite.
The helium atoms were locked in apatite grains as they cooled and moved closer to the surface during the carving of the Grand Canyon, she said.
The hotter the apatite was the fewer helium atoms remained within it - allowing scientists to get a thermal history of the area.
Since temperature variations at shallow levels beneath the Earth's surface are influenced by topography, this allowed the team to infer how much time had passed since there was significant natural excavation of the Grand Canyon.
"Our research implies that the Grand Canyon was directly carved to within a few hundred metres of its modern depth by about 70 million years ago," Flowers said.
She said that different canyon segments may have evolved separately before joining into what visitors see today.
In a 2008 study, Flowers and colleagues showed that parts of the eastern section of the Grand Canyon likely developed some 55 million years ago.
Flowers also suggests that it was carved by an ancestor of the Colorado, which flowed in the opposite direction.
"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," she said.
The study was published in the journal Science.
