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How and When Did the Grand Canyon Form?

The Grand Canyon was cut away by the flow of the Colorado River, but one question is still debated: when exactly did this erosion happen?

By
Sabrina Stierwalt, PhD,
Episode #279

the grand canyon

In the northwest corner of the state of Arizona, the Grand Canyon stretches 277 miles (446 km) long and 18 miles (29 km) at its widest. The canyon cuts as deep as a little over a mile (or 1800 m).

Named Ongtupqa in the Hopi language, the canyon is considered a passageway to the afterlife. The United States government gave the Grand Canyon national park status when President Woodrow Wilson signed the Grand Canyon National Park Act in 1919. The canyon is also home to 373 species of birds, 91 species of mammals, 58 species of reptiles and amphibians, and 18 species of fish, and sees over 5 million visitors each year.

Our fascination with the Grand Canyon has led to thousands of studies of its layered rock, its marine and terrestrial fossils, and its wildlife inhabitants. Geologists agree that the layers of colored rock that form the canyon’s walls are as old as 1.8 billion years. Scientists also agree that the great crevice in the Earth’s surface was cut away by the flow of the Colorado River. However one question is still debated: when exactly did this erosion happen?

When Did the Grand Canyon Form?

The region we now know as the Grand Canyon has changed dramatically over our planet’s history, at different times hosting multiple mountain ranges. Those mountains were eventually worn down by rain, wind, and frost until finally forming a plateau that was slowly but consistently carved little by little by the flow of the Colorado River.

There is substantial evidence that the Grand Canyon formed around 5 to 6 million years ago, and geologically speaking, that’s very recent. One spot that suggests to geologists that the Canyon is so young is known as Muddy Creek, home to a buildup of gravel, limestone, and lava. The lack of the type of sediment normally found in the Colorado River suggests the region was formed prior to the Colorado River passing through. If the river could not have exited the canyon through this spot any earlier than 5 to 6 million years ago, this sets an approximate upper limit to the age of the canyon.

But the findings from a few recent studies have begun to support the longstanding theory that the Grand Canyon was actually formed by the merging of two smaller “ancestral” canyons, one in the east and one in the west. In a 2012 study published in the journal Science, a team of geologists led by Professor Rebecca Flowers of the University of Colorado, Boulder, examined the concentrations of helium in different samples of rock from the east and west ends of the canyon.

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