The Grand Canyon, or at least most of it, isn’t as old as we thought

There's been a spirited debate among geologists about the age of the Grand Canyon — with some studies showing that the canyon formed as soon as 5-6 million years ago, while others have found that it's as much as 70 million years old. Now, a new study seems to tie everything together, though, possibly putting the debate to rest.

The Grand Canyon, located in northern Arizona, is almost 450 kilometres long, and it's divided into five different sections — (from west to east) Westernmost Grand Canyon, the Hurricane fault segment, the Muav Gorge, Eastern Grand Canyon, and Marble Canyon. The layers of rock that line the canyon's cliffs show off nearly 2 billion years of Earth's geological history, however studies about exactly when those layers of rock were exposed by the carving action of the Colorado River and other water ways have turned up some varied results. Now, a team of researchers led by Karl Karlstrom, from the University of Arizona, as examined four of the five different sections of the canyon, and found that they have a range of different ages.

Using a few different methods to analyse rocks taken from both the rim and down at river level, the researchers found that two of the middle sections of the canyon are the oldest — the Hurricane fault section at between 70 and 55 million years old and Eastern Grand Canyon at between 25 and 15 million years ago, with each being carved by different rivers. The two sections at either end — the Westernmost Grand Canyon and Marble Canyon — are far younger, around 5 or 6 million years old, carved when the Colorado River began flowing through the area.

"Different segments of the canyon have different histories and different ages, but they didn't get linked together to form the Grand Canyon with the Colorado River running through it until 5 to 6 million years ago," Karlstrom told Huffington Post.

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"Overall, I think they've done a really good job," Peter Reiners, a geochemist at the University of Arizona in Tucson who was not part of the study, told National Geographic. "This new model isn't just a compromise of all previous notions; it's recognition that a big river can have a complicated history."

Not everyone in the field is on board with Karlstrom and his team's results, though. Apparently, their study assumed a range of different temperatures for the air the rocks were exposed to, whereas other studies assume a constant of 25 degrees C. A wider range can can lead to different values for how long the rocks have been exposed.

Brian Wernicke, a Caltech geoscientist was especially concerned about the temperature range used, according to Huffington Post, saying that Karlstrom and his team aren't thinking things through.

"The new model seems to be much too complicated," Wernicke told National Geographic.

(Images courtesy: K. Karlstrom/Univ. of Arizona, L. Crossey/Univ. of New Mexico)

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