Grand Canyon May Be Older (And Younger) Than You Think

Jan 27, 2014
Originally published on January 27, 2014 11:31 am

In recent years geologists have hotly debated the age of the Grand Canyon. Some think it's young (just 6 million years old), while others argue that it dates back 70 million years — to the days of dinosaurs.

Now one group says the Grand Canyon is neither young nor old. Instead, these geologists say, it's both.

In the journal Nature Geoscience, Karl Karlstrom, of the University of New Mexico, and some colleagues describe a new creation story for the Grand Canyon. They think that about 6 million years ago, a river zigzagging a path across the Colorado plateau found part of its way through canyons that already existed.

So, although the Grand Canyon as a whole is relatively young, they say, a couple of sections are ancient.

"We're making a major leap from thinking of a canyon that has a simple history ... to a more sophisticated understanding of how landscapes actually evolve through time," Karlstrom says.

It wasn't too long ago that scientists generally agreed on a simpler history. Karlstrom was part of the team that developed a walking path called the Trail of Time along the south rim of the Grand Canyon. Signs there tell visitors that the Colorado River carved the Grand Canyon in the past 6 million years.

"The Trail of Time exhibit has what we considered at the time, in 2010, to be the scientific consensus," says Karlstrom, who hiked the canyon as a kid and has studied it professionally for 30 years.

Figuring out when a canyon was cut is not easy, he says, because rivers do their sculpting through erosion.

"Erosion takes away material, and so geologists are left without the rock record," he explains, "without the physical evidence of the carving. What you are left with is a landscape, a land form."

Scientists have started using sophisticated new techniques that can reconstruct the history of erosion by analyzing the chemistry of one of the minerals in canyon rocks. And in 2012, a research team used those techniques to make the controversial claim that the Grand Canyon was actually cut about 70 million years ago — in the Late Cretaceous. Experts like Karlstrom were startled.

"That whole episode — Is it old? Is it young? — caused my group to rethink what we meant by 'old' and 'young,' " he says. "And what is the evidence?"

Not everyone thinks the latest findings will be the last word. Brian Wernicke, a geologist at the California Institute of Technology, is in the camp that leans toward a more ancient Grand Canyon, and doesn't buy all of the arguments of Karlstrom and his colleagues.

But to him, the important thing is that this report shows a real shift in thinking. The monolithic view of a young canyon no longer dominates, Wernicke says. "That's not the discussion right now. We've all learned that it's a lot more complicated than that."

Wernicke says he expects that over the next year, there will be more data and more debate.

And all of this is exciting for a scientist, Karlstrom says. "It's spectacular. If you're willing to change your mind based on evidence, it's great fun."

Now when he takes river trips through the canyon, he says, he sees everything with new eyes.

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Transcript

STEVE INSKEEP, HOST:

For all the people who have looked at the Grand Canyon - the visitors who have peered over the edge, the tourists in helicopters who've flown overhead, the producers who filmed that special three-part "Brady Bunch" episode - nobody knows how old it is. Some scientists say the Grand Canyon is young, in relative terms, just six million years old, while others argue that it dates back to the days of the dinosaurs, much earlier. NPR's Nell Greenfieldboyce reports that one group now thinks it has the answer.

NELL GREENFIELDBOYCE, BYLINE: At the south rim of the Grand Canyon, there's a walking path called the Trail of Time. It uses the Grand Canyon's awesome scenery and rocks to try to convey the vastness of geologic time. And it tells tourists that the Colorado River carved the Grand Canyon in the last six million years.

KARL KARLSTROM: The trail of time exhibit has what we considered at the time, in 2010, to be the scientific consensus on the age of Grand Canyon, and that's five to six million years old.

GREENFIELDBOYCE: Karl Karlstrom is a geologist at the University of New Mexico who worked on the exhibit. He hiked the canyon as a kid and has studied it professionally for 30 years. He says figuring out when a canyon was carved is not easy because rivers carve canyons through erosion.

KARLSTROM: And erosion takes away material and so geologists are left without the rock record, without the physical evidence of the carving. What you are left with is a landscape, a land form.

GREENFIELDBOYCE: In recent years, scientists have started using sophisticated new techniques that can reconstruct the history of erosion by analyzing the chemistry of one of the minerals that make up canyon rocks. And in 2012, one research team concluded that the Grand Canyon was actually cut about 70 million years ago, in the late Cretaceous, which startled experts like Karlstrom.

KARLSTROM: That whole episode - is it old, is it young - caused my group to rethink what we meant by old and young and what is the evidence.

GREENFIELDBOYCE: Now, in the journal Nature Geoscience, he and some colleagues describe a new creation story for the Grand Canyon. They say it is neither old nor young; rather, it's both. They think that about six million years ago, a river forging a zigzagging path across the Colorado plateau found part of its way through old canyons that already existed which means that although the Grand Canyon as a whole is relatively young, a couple of sections are more ancient.

KARLSTROM: We're making a major leap from thinking of a canyon that has a simple history, it was all carved at once either at 70 or at five to six, to a more sophisticated understanding of how landscapes actually evolve through time.

GREENFIELDBOYCE: Not everyone thinks this will be the last word. Brian Wernicke is a geologist at Caltech who is in the more ancient Grand Canyon camp. He doesn't buy all the arguments in this new paper. But to him, the important thing is that it shows a real shift in people's thinking.

BRIAN WERNICKE: In the mid-2000s there was this monolithic view that oh, yeah, the Grand Canyon is very young and it was cut six million years ago by the Colorado River which was born six million years ago. OK? That's not the discussion right now. We've all learned that it's a lot more complicated than that.

GREENFIELDBOYCE: He expects that over the next year, there will be more data and more debate. Karl Karlstrom says, for a scientist, all this is exciting.

It's spectacular. You know, if you're willing to change your mind, based on evidence, it's great fun.

He says now, when he takes river trips through the canyon, he sees it with new eyes. Nell Greenfieldboyce, NPR News.

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