A gigantic line of cliffs may once have stretched for thousands of kilometers across ancient North America, helping erase more than a billion years of geological history from rocks now exposed in the Grand Canyon.
Scientists led by the University of Southampton in the UK believe this enormous landscape formed about 800 million years ago, when the ancient supercontinent Rodinia began breaking apart.
The researchers estimate that the cliffs may have stood around one kilometer high and extended across a huge portion of what is now the United States.
Over millions of years, erosion along this “mega-escarpment” could have removed several kilometers of rock, eventually exposing some of the oldest rocks found in North America.
The findings, published in the journal Geology, could help explain one of the Grand Canyon’s biggest mysteries.
The canyon contains rocks recording nearly 2 billion years of Earth’s history. But parts of that history are strangely absent. In some places, very old rocks sit directly beneath much younger layers, with rocks representing more than a billion years missing in between.
Geologists call this enormous gap the Great Unconformity.
Professor Thomas Gernon, who led the study, and his colleagues believe the missing rocks may have been stripped away long before the Colorado River carved the Grand Canyon we recognize today.
The story begins with Rodinia, a supercontinent that brought much of Earth’s land together hundreds of millions of years before the better-known supercontinent Pangaea.
When Rodinia started breaking apart, powerful geological forces stretched and lifted parts of North America. The researchers propose that this process created an enormous line of steep cliffs along the edge of the continent.
The ancient cliff system may have passed through areas that are now Arizona, Utah, Idaho, Wyoming, Colorado, Texas, Oklahoma, Arkansas, Missouri and Illinois.
Using reconstructions of ancient moving continents together with computer models of changing landscapes, the scientists examined how these cliffs may have evolved.
They found that the Grand Canyon region occupied a position similar to areas near major cliff systems that exist today in places such as South Africa and Brazil.
As the ancient cliffs gradually moved inland through erosion, rivers and possibly glaciers could have removed extraordinary amounts of material. The researchers estimate that as much as eight kilometers of rock may have disappeared in some areas.
That agrees with other geological evidence suggesting that roughly five to 10 kilometers of rock were removed from parts of the region long before today’s Grand Canyon existed.
The ancient landscape may also have influenced the direction of rivers, where sediments accumulated and how rising seas later spread across North America.
Understanding this lost landscape could therefore help scientists reconstruct a much larger chapter of Earth’s history.
The researchers say similar ancient cliff systems may also explain mysterious gaps in rock records elsewhere in the world.
The Grand Canyon, in other words, may be telling two very different stories: the familiar story of a spectacular canyon carved relatively recently in geological time, and a much older story of towering cliffs that helped strip away a billion years of history before the canyon even existed.
