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 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.