A Vanished Mega-Cliff May Explain the Grand Canyon’s Missing Billion Years

The Grand Canyon’s deepest rocks may have been exposed by a colossal cliff system long before the Colorado River carved the canyon visible today, according to research reported by ScienceDaily from the University of Southampton. The study proposes that a “great escarpment” formed roughly 800 million years ago, as the supercontinent Rodinia began breaking apart. The cliff system may have stood about one kilometer high and stretched for thousands of kilometers across what is now western and central North America. Researchers suggest the ancient escarpment extended through areas that today include Arizona, Utah, Idaho, Wyoming, Colorado, Texas, Oklahoma, Arkansas, Missouri and Illinois. As erosion wore down the elevated landscape over tens of millions of years, it may have removed as much as eight kilometers of rock in some places. That process could have brought ancient crystalline basement rocks to the surface, including those now visible in the Grand Canyon. The canyon preserves geological evidence dating back about two billion years, but more than half of that record appears to be missing. This gap is part of the Great Unconformity, a geological boundary in which rocks representing more than a billion years are absent. The researchers combined plate-tectonic reconstructions with models of landscape development to recreate the region’s possible ancient form. Their results indicate that the future Grand Canyon occupied a position near the edge of the continent comparable to the locations of major escarpments found today in South Africa and Brazil. According to the study, tectonic uplift caused by continental rifting created steep slopes and high ground that rivers and glaciers could erode. Geological evidence from the region independently suggests that between five and 10 kilometers of rock disappeared before the modern canyon formed. The proposed landform may also have influenced river routes, sediment deposits and the timing of rising seas across ancient North America. The research was published in Geology by scientists from the University of Southampton, GFZ Helmholtz Centre for Geosciences, the University of Potsdam and the University of Illinois Urbana-Champaign. The authors present the escarpment as a possible explanation for the uneven erosion associated with the Great Unconformity, rather than as a surviving physical feature. The cliff system itself has since vanished through erosion and geological change.