The Grand Canyon is a geological Frankenstein, made of old and new canyon parts, according to new research published in the Jan. 26 issue of Nature Geoscience. The work may be the beginning of the end a very long debate that has put the canyon at anywhere from 70-million-years-old to as young as 5 or 6 million-years-old.

"I think we've got the solution to a 140-year-old problem," said Karl Karlstrom of the University of New Mexico in Albuquerque.

The solution comes in the form of a technique called apatite fission-track dating which allow geologists to determine how long rocks of the canyon have been cooled from the steamy warmth a kilometer or two underground, to the chilly surface temperature of the Earth -- what is called their thermal histories.

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By figuring out the thermal histories of rock samples taken from the base of different segments of the Grand Canyon and the adjacent canyon rims 1,500 meters above, Karlstrom and his colleagues were able to determine how long ago the rocks were unearthed by the canyons, which were being cut by a river.

They found that two of the three middle segments, the Hurricane segment and the Eastern Grand Canyon, formed 70 to 50 million years ago and 25 to 15 million years ago, respectively. On the far ends of the canyon they dated Marble Canyon to the east and the Westernmost Grand Canyon to the past 5–6 million years.

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So although the middle parts of the canyon are old, the team concludes that it was the modern Colorado River that stitched the old and new together to make today's Grand Canyon.

"The new dating techniques have really opened up a lot of ideas," said geologist James Sears of the University of Montana. Sears is among those trying to work out the ancient route the ancestral Colorado River took, long before it turned south. "The river needs somewhere to go before 5 million years ago; before capture by the Gulf California." He thinks it went north -- all the way to Hudson Bay. But that's another story.

The Grand Canyon's inner gorge shown here was carved in the last 6 million years by the powerful Colorado River.Laura Crossey, UNM

Other researchers who have used different variations of the apatite fission-track dating technique in the Grand Canyon have found some rocks which agree with the new work, and some that don't.

"Their new results appear to agree to first order with our inferred Grand Canyon carving history everywhere except in the westernmost Grand Canyon," explained geologist Becky Flowers of the University of Colorado, Boulder. There are other differences, however. "...t will take a bit more time to understand fully why their interpretations are so different from ours and why they conclude that the erosion history varied so dramatically within this short reach of the canyon."

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That said, the new thermal histories seem on the verge of cracking the tough geological puzzle that the Grand Canyon has posed ever since John Wesley Powell first set his geologically trained eyes on it in 1869.

"It is exciting that it is generating more discussion over Grand Canyon evolution," Flowers said.