LOS ANGELES – The awe-inspiring Grand Canyon was probably carved about 70 million years ago, much earlier than thought, a provocative new study suggests – so early that dinosaurs might have roamed near this natural wonder.
Using a new dating tool, a team of scientists came up with a different age for the gorge’s western section, challenging conventional wisdom that much of the canyon was scoured by the mighty Colorado River in the last 5 million to 6 million years.
Not everyone is convinced with the latest viewpoint published online Thursday in the journal Science. Critics contend the study ignores a mountain of evidence pointing to a geologically young landscape, and they have doubts about the technique used to date it.
How the Grand Canyon became grand – with its vertical cliffs and flat plateaus – has been debated since John Wesley Powell scouted the sheer walls during his famous 1869 expedition.
Though the exposed rocks are ancient, most scientists believe the Grand Canyon itself was forged in the recent geologic past, created when tectonic forces uplifted the land that the Colorado River later carved through.
The new work argued that canyon-cutting occurred long before that. To come up with the age, the team crushed rocks collected from the bottom of the canyon to analyze a rare type of mineral called apatite. The mineral contains traces of radioactive elements that release helium during decay, allowing researchers to calculate the passage of time since the canyon eroded.
Their interpretation: The western Grand Canyon is 70 million years old and was likely shaped by an ancient river that coursed in the opposite direction of the west-flowing Colorado.