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(Photo Credit: Roger Bolsius)
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The Grand Canyon is one of the most iconic natural landmarks
in North America. Located in Arizona,
its age has been hotly disputed amongst geoscientists. Traditionally, the canyon was believed to
have been cut 5-6 million years by the Colorado River. In 2012 a research team
used uranium-track dating of minerals in the rocks to make the controversial
claim that the Grand Canyon was actually cut about 70 million years ago. So who
is right?
According to a study recently published in the journal
Nature Geoscience, the solution is not a question of old or young but of old
and young --- parts of the canyon date back to the age of the dinosaurs while
other parts were inscribed 6 million years before the present. The scientists divided the canyon into five
different sections: Marble Canyon, Eastern Grand Canyon, Muav Gorge, Hurricane
fault segment, and Westernmost Grand Canyon.
They found that the outermost segments, the Marble Canyon and
Westernmost Grand Canyon, date to 5-6 Ma (million years). The canyon’s age increases towards the
center, with the Eastern Grand Canyon dating 15-25 Ma and Hurricane fault
Segment to 65-50 Ma.
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Map of the
Grand Canyon with five sections labeled; modified from Karlstrom et al. (2014)
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The research team based out of the University of New Mexico used fission track dating, analyzing the trails of uranium isotopes. This technique is similar to carbon dating, measuring the decayed daughter isotopes to determine ages. Unlike carbon dating, uranium dating can be used to determine the ages of rocks that are millions of years old rather than thousands.
So the big picture --- what do these different dates mean
for the evolution of the canyon? Parts
of the canyon (Eastern Grand Canyon and Hurricane fault segment) existed
pre-Colorado River. The stratigraphy
shows that the Hurricane fault segment had been inscribed to about half of its
current depth by a paleoriver. It never
connected to the Eastern Grand Canyon, which was partially carved out 15-25
Ma. The Colorado River carved out the
Marble Canyon and Westernmost Grand Canyon, linking up with the other sections
in the process.
More information can be found in the original Nature Geoscience article “Formation
of the Grand Canyon 5 to 6 million years ago through integration of older
palaeocanyons," authored by Karl E. Karlstrom, John P. Lee, Shari A.
Kelley, Ryan S. Crow, Laura J. Crossey, Richard A. Young, Greg Lazear, L. Sue
Beard, Jason W. Ricketts, Matthew Fox and David L. Shuster.
