Finally tonight: Just how old is the Grand Canyon? The conventional wisdom holds that this natural wonder of the world was shaped by the Colorado River about five or six million years ago.But there's been a long-running debate over whether it's much older. And, yesterday, researchers published a study in the journal "Science," arguing these majestic formations were formed by two much older rivers cutting through the landscape some 70 million years ago.That was during the age of the dinosaurs. We have NewsHour science correspondent Miles O'Brien here to tell us what the debate is all about. So, Miles, from six million to 70 million years, is that scientifically as big a gap as it appears?Yes, it's a big deal. And there is a big debate in the scientific community right now over it, Margaret.When you look at the Grand Canyon, as a layperson―we have been there and see it―you would say,well, clearly, the Colorado River formed this over many millions of years. And we know the Colorado River is between five and six million years old, no scientific debate there. There is plenty of evidence on that.So, you would say, well, the canyon must be that old. Well, this new paper which came out―Becky Flowers of the University of Colorado, along with Ken Farley at Caltech, took a series of readings on the eastern and western portions of the river,which measured a helium isotope which stops escaping at about 70 degrees. You can tell how the rocks have been rising out of center of the earth and sort of pinpoint where the depth would be.And they came to the conclusion that there was a Grand Canyon there some 70 million years ago before the river. Well, how would that be?
