One of the most remarkable landscapes in the world, the Grand Canyon in the U.S. state of Arizona has long been the focus of tourists the world over. The prevailing theory for the creation of the Grand Canyon is that the Colorado River carved its way through some six million years ago.
However, new research by researchers from the University of Colorado at Boulder and the California Institute of Technology has added some 40 to 50 million years to the Grand Canyon’s age.
Using a technique known as radiometric dating, the team dated rocks from within the canyon and surrounding plateaus that had been deposited near sea level, at a time before the Grand Canyon was present.
"As rocks moved to the surface in the Grand Canyon region, they cooled off," said Flowers, referring to the movement away from the warmer levels closer to the Earth’s core. "The cooling history of the rocks allowed us to reconstruct the ancient topography, telling us the Grand Canyon has an older prehistory than many had thought."
The research team believes that the eastern section of the Grand Canyon formed 55 million years ago, only later linking up with other segments of the canyon which had evolved separately. "It's a complicated picture because different segments of the canyon appear to have evolved at different times and subsequently were integrated," Flowers said.
The underlying theory is that about 80 million years ago, geological forces pushed the Colorado Plateau upwards. An old river flowed across the plateau at the time, creating what they’ve loosely termed the ‘proto-canyon’, and then over the next few million years’ streams began to erode away at the land. In time, the top 2,000 meters of the entire plateau was eroded, until it formed the canyon that we know of today.
"We're seeing a record of an ancestral Grand Canyon that was incised in rocks above the Grand Canyon and subsequently lowered to its present state," says Rebecca Flowers of the University of Colorado, Boulder.
The team used apatite from within the canyon’s sandstone walls – which host traces of uranium and thorium – which expel helium atoms as they decay. The abundance of these three elements, in tandem with temperature information from Earth’s interior, allowed the team to create a geological clock. This allowed them to calculate when the apatite grains were embedded in rock a mile deep – the depth of the current canyon – and when they cooled as they neared Earth’s surface as a result of erosion.
"I was surprised. I didn’t believe the results at first," says co-author Brian Wernicke, a geologist at the California Institute of Technology in Pasadena. "That canyon has survived all that erosion up until the present day."
Joshua Hill, a Geek’s-Geek from Melbourne, Australia, Josh is an aspiring author with dreams of publishing his epic fantasy, currently in the works, sometime in the next 5 years. A techie, nerd, sci-fi nut and bookworm.
