A Billion-Year-Old Missing Cliff May Explain the Grand Canyon's Puzzling Gap

Scientists led by the University of Southampton have found evidence that an enormous ancient cliff system may have helped expose the oldest rocks of the Grand Canyon almost a billion years before the Colorado River began carving today's landscape.

The team says this "great escarpment" formed around 800 million years ago as the supercontinent Rodinia broke apart. The cliffs may have stood roughly a kilometer high and stretched for thousands of kilometers across what is now western North America, before erosion gradually wore them down and exposed ancient crystalline basement rock — the kind now visible deep in the Grand Canyon in Arizona.

Thomas Gernon, professor of Earth Science at Southampton and the study's lead author, said the Grand Canyon's rock record stretches back about two billion years, yet more than half of it is missing. The team argues the escarpment's erosion explains that gap, known as the Great Unconformity.

By combining reconstructions of plate tectonic movement with data on how landscapes change over time, the researchers estimated the escarpment could have stripped away as much as eight kilometers of rock in places — a figure that matches independent geological evidence of five to ten kilometers of rock loss in the region before the modern canyon formed. The escarpment likely crossed areas that are today Arizona, Utah, Idaho, Wyoming, Colorado, Texas, Oklahoma, Arkansas, Missouri and Illinois.

The study, published in the journal Geology, involved researchers from Southampton, the GFZ Helmholtz Centre for Geosciences and the University of Potsdam in Germany, and the University of Illinois Urbana-Champaign. The researchers say the ancient mountain rim may also have shaped river paths and sediment deposits across the region before the Cambrian explosion, the period when complex life diversified rapidly.