The Grand Canyon is How Old?

(Photo Credit: Roger Bolsius)

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. 

Map of the Grand Canyon with five sections labeled; modified from Karlstrom et al. (2014)

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.