Washington, April 10 : A new research has challenged the long-held belief that the Grand Canyon in the US was carved by the Colorado River about six million years ago, with analysis suggesting that parts of the canyon were formed more than 50 million years earlier than previously thought.
According to a report in National Geographic News, the newfound evidence shows that part of the canyon known as Upper Granite Gorge formed more than 55 million years ago.
"The history of the Grand Canyon is far more complicated than previously believed," according to Rebecca Flowers, a professor at the University of Colorado, Boulder and the research paper's lead author.
"What this tells us is that the entire Grand Canyon didn't suddenly just form six million years ago. Instead, the giant chasm may have formed as a series of "ancestral" canyons grew and joined together," she added.
Scientists have long argued over how the Grand Canyon, arguably one of the best known and most beautiful landscapes on Earth, was formed.
The most widely held belief was that it was created when geological forces lifted the area and the Colorado River cut down through the resulting plateau.
The canyon's age had been pegged at about six million years based on sediment deposited by the Colorado as it exited the canyon around Lake Mead.
The new study used a different technique, a method of dating rocks developed by geologists at the California Institute of Technology called uranium-thorium-helium dating.
By measuring the amounts of uranium and helium contained in samples collected from the Upper Granite Gorge, the researchers could determine the time at which rocks there cooled, indicating when they were unearthed by erosion.
Because temperatures are hotter below Earth's surface, these cooling rates helps scientists determine when rocks were buried deep underground, and when the forces of erosion exposed them to cooler temperatures closer to the surface.
The results showed that the rocks in Upper Granite Gorge were exposed to cooler temperatures near Earth's surface around 55 million years ago.
It also showed that both the rim and the bottom of the gorge had cooled at the same time, suggesting that the gorge formed from previously existing canyons that eventually connected, rather than a plateau.
"If there had not been a canyon, the gorge and rim samples would have been different," noted Brian Wernicke, a geology professor at Caltech.
"This is a strong addition of data that helps to document what has been proposed-that ancestral canyons existed and became linked together," said Karl Karlstrom, a geologist at the University of New Mexico.