It’s doubtful whether the millions who visit the Grand Canyon each year give much thought to when or how it was formed, but the topic has long been the subject of scientific debate.
Now a new study from the University of Colorado suggests the canyon may be much older than was previously thought.
The Grand Canyon
Perhaps with a nod to the scientific controversy, the Grand Canyon National Park website is cagey about the age of its central attraction, describing it only as ‘late Cenozoic’ (the Cenozoic covers roughly the last 65 million years, from the extinction of the dinosaurs at the end of the Quaternary to the present day).
But perhaps it’s inevitable that it’s proving difficult to date with any certainty, a topographic feature that’s “immense, averaging 4,000 feet deep for its entire 277 miles.
It is 6,000 feet deep at its deepest point and 18 miles at its widest” according to Grand Canyon National Park.
It’s unlikely that a geological feature of this scale will have formed at one time and the chances are that a number of different stages were involved across a considerable period of time. The University of Colorado research proposes the earliest date yet – suggesting that parts of the canyon may have formed as much as 70 million years ago, just predating the Cenozoic era.
Grand Canyon Study Findings
The researchers dated the origin of the canyon through analysing the decay of atoms of uranium and thorium to form helium isotopes. These atoms occur in a mineral called apatite and their presence records important information about the temperature and pressures at which they were formed – allowing researchers to determine a time and elevation for that formation.
“Whether helium is retained or lost from the individual crystals is a function of temperatures in the rocks,” the report’s lead author, Assistant Professor Rebecca Flowers told Decoded Science. “Temperature variations at shallow levels beneath the Earth’s surface are influenced by topography, and the thermal history recorded by the apatite grains allowed us to infer how much time had passed since there was significant carving of the Grand Canyon. In other words, rocks cool as they approach the Earth’s surface by erosion, and our data record this cooling history.”
Grand Canyon Age Study: Wider Applications
The results of the analysis put the date of excavation of the canyon back far beyond the conventionally accepted date of just a few million years ago. “The most important finding of our study is that it provides evidence that the western Grand Canyon was carved to within a few hundred meters of modern depths by ~70 Ma,” said Professor Flowers.
So why does it matter how old the Grand Canyon is? Well, knowing how and when such a major topographical feature was formed will help to improve scientists’ understanding of the evolution of the region. According to Professor Flowers, “this history has significant implications for the evolution of topography, landscapes, hydrology, and tectonism in the western U.S.”
Flowers R.M. and Farley K.A. Apatite 4He/3He and (U-Th)/He evidence for an ancient Grand Canyon. (2012). Science. Accessed November 29, 2012.
Grand Canyon National Park. Geologic formations. (2012). Accessed 28 November 2012
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