Grand Canyon Millions of Years Older Than Thought?

Anne Minard in Flagstaff, Arizona
for National Geographic News

March 6, 2008

In a week when massive flooding (see photo) is turning back the clock a bit for the Grand Canyon, a controversial new study is shedding light on just how far back the canyon's history goes.

The vast gorge may have been formed millions of years earlier than thought, the report says. The findings fly in the face of long-standing theory.

The traditional view is that the massive gorge is a uniform six million years old, and that the Colorado River is almost entirely responsible for carving the Arizona canyon.

But the new study says the western reaches of the Grand Canyon began forming 17 million years ago, thanks to slow erosion that started before the river existed.

The researchers also found that the eastern half formed within the past four million years—not six million—as the river cut into the Colorado Plateau.

The scientists based their research on clues tucked within caves in canyon walls.

Compiled by lead author Victor Polyak and colleagues at the University of New Mexico, the results will appear in tomorrow's issue of the journal Science—and they will likely be hotly contested, experts say.

(See photos of the Grand Canyon.)

New Technology

Until now, efforts to describe the Grand Canyon's formation relied on geologic events such as rock flows and deposits of sedimentary rock.

But those records are only reliable to about a million years ago, the authors write.

So Polyak and his colleagues reasoned that as water cut down into northern Arizona's rock layers—forming the canyon walls—the surrounding water table dropped alongside it.

So they looked at calcite deposits that form in caves at the edge of a dropping water table, called speleothems.

Polyak and colleagues knew speleothems form where a water table is dropping: They've seen similar formations in caves throughout deserts of the U.S. Southwest.

The Grand Canyon speleothems contain minute traces of lead and uranium, and ratios of these elements can pin the formations to a specific place and time.

Study of carbonate deposits at or near the water table led the researchers to conclude that the canyon is oldest at its western end and that it opened up steadily to the east through erosion.

(Learn how erosion sculpts nature.)

Outrage

Grand Canyon geologists have long focused on geologic clues, such as traces of volcanic activity, to estimate the age of the canyon. The new, cave deposit-based approach is hard to swallow for some scientists.

One of them is Ivo Lucchitta, a Flagstaff, Arizona, geologist.

Lucchitta said he is "outraged" about the new research.

He said he will join other long-time Grand Canyon geologists in blasting Science for what he says is inadequate vetting of the new study.

There is "a host of published information by many researchers having to do with the issue presented by these authors, and this information is squarely at odds with what these folks propose," he said. "But [Science] completely ignore[s] it."

"If the authors really want to make a contribution, they have to show us why the interpretations that have issued previously … are wrong, and why their interpretations and data are sounder," Lucchitta said.

A Grand Discovery?

But Wayne Ranney—a Flagstaff geologist and author of the book Carving Grand Canyon—said the authors may have found the "smoking gun" on when and how the Grand Canyon was formed.

Ranney said he will make room for the new idea in the next printing of his book.

"I'd be awfully surprised if this work doesn't generate a lot of traction with canyon geologists, since it fits well with many emerging ideas in the last few years," he said.

But the authors say they've only started to use this isotopic technology to describe the canyon's history.

Hundreds of deposits probably exist throughout the canyon, they say.

Those deposits may offer the potential to reconstruct the canyon's history "with a resolution perhaps high enough to explain complexities of the canyon's … faults, folds, and volcanic and tectonic activity," said study co-author Carol Hill.

Though Hill and her team may tackle some of that work, much of it may be left to future generations of scientists, she said.

"We're kind of just showing the way, because this has never been done before."

Free Email News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).