Dating of rock erosion pegs the ancient chasm as 70 million years old
Rock of ages it may be, but the Grand Canyon’s age itself is under fire. New work suggests the iconic chasm was already in place 70 million years ago — making it far older than commonly believed.
By most geologists’ definition, the Grand Canyon proper emerged between 5 million and 6 million years ago, as the Colorado River flowed across and eroded its way through layer after layer of rock. Evidence for this age comes from, among other things, great piles of washed-out gravel at the canyon’s western end that appeared around that time.
But the new study, reported online November 29 in Science, looks instead at the chemistry of rocks exposed throughout the canyon. Rocks