Originally published December 1 2012
Grand Canyon may be 60 million years older than previously thought
by David Gutierrez, staff writer
(NaturalNews) The Grand Canyon may be 60 million years older than scientists had previously believed, according to a study conducted by researchers from the University of Colorado-Boulder and the California Institute of Technology, and published in the journal Science.
"Our research implies that the Grand Canyon was directly carved to within a few hundred meters of its modern depth by about 70 million years ago," study co-author Rebecca Flowers said.
That would mean that the canyon existed in roughly its current form for five million years before the extinction of the dinosaurs.
The Grand Canyon is 280 miles long, reaching depths of a mile and widths of up to 18 miles. Scientists believe that the canyon was carved mostly by the waterway that eventually became the Colorado River, although the waterway initially flowed in the opposite direction of the modern river.
Molecular clock
The researchers arrived at the shocking find using a new dating method based on the fact that in a mineral known as apatite, radioactive uranium and thorium atoms naturally decay into helium over time. These helium atoms then naturally work their way through tiny crevices in the rock and out to the surface, where they dissipate into the air. Significantly, the rate at which helium disperses is strongly determined by temperature: at temperatures below 86�F, no helium disperses; at temperatures above 158�F, all of it does.
Therefore, the researchers examined the presence of helium in apatite from the Grand Canyon, and used that to map the temperatures that the rocks had been exposed to over time.
"The main thing this technique allows us to do is detect variations in the thermal structure at shallow levels of the Earth's crust," Flowers said. "Since these variations are in part induced by the topography of the region, we obtained dates that allowed us to constrain the time frame when the Grand Canyon was incised."
To get a more detailed picture, the researchers also looked at where the helium atoms were distributed in the individual rocks.
"Knowing not just how much helium is present in the grains but also how it is distributed gives us additional information about whether the rocks had a rapid cooling or slow cooling history," Flowers said.
Flowers said that she expects the findings to spark a controversy, as scientists are currently divided over the true age of the canyon. In part, this uncertainty comes from the fact that the canyon appears to have formed in several different segments, perhaps at different times.
Most scientists place the age of the canyon at five to six million years old, based on the age of gravel carried by the ancestral Colorado River. In 2008, a study dated the canyon to 17 million years old based on mineral deposits found in caves in the canyon walls. The same year; however, Flowers and colleagues dated the eastern portion of the canyon to 55 million years ago - but noted that at that time, the bottom of the canyon was higher up than the rim of it is today.
Sources:
http://www.sciencedaily.com/releases/2012/11/121129143301.htm
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