Scientists have uncovered evidence that an enormous ancient cliff system may have helped expose the deepest rocks of the Grand Canyon nearly a billion years before the Colorado River began carving the landscape seen today.
Led by researchers at the University of Southampton in the UK, the new study suggests that a vast “great escarpment” formed about 800 million years ago as the supercontinent Rodinia broke apart.
These towering cliffs may have reached roughly a kilometer in height and extended for thousands of kilometers along western North America. Over time, erosion along this immense rocky boundary removed huge amounts of material, eventually exposing ancient crystalline basement rocks that can now be seen in the Grand Canyon in southern Arizona.
A Billion Years Missing From the Grand Canyon
Thomas Gernon, Professor of Earth Science at the University of Southampton and lead author of the study, explained that the Grand Canyon preserves a geological history stretching back about two billion years. Yet more than half of that rock record appears to be absent.
He said: “Our paper suggests the Canyon’s basement rocks were progressively brought to the surface as part of an immense escarpment that developed during the breakup of an ancient supercontinent.
“The findings also shed light on the formation of the Great Unconformity, a mysterious gap in the rock record that spans over a billion years.”
Published in Geology, the research involved scientists from the University of Southampton, GFZ Helmholtz Centre for Geosciences and University of Potsdam, both in Germany, and the University of Illinois Urbana-Champaign in the USA.
The researchers propose that this ancient escarpment crossed areas that today include Arizona, Utah, Idaho, Wyoming, Colorado, Texas, Oklahoma, Arkansas, Missouri and Illinois.
Prof Gernon said powerful erosion across this enormous region eventually uncovered some of the oldest rocks in North America, with the Grand Canyon providing the best known example.
Reconstructing a Lost North American Landscape
To investigate what the region may have looked like hundreds of millions of years ago, the team combined reconstructions of plate tectonic movements with data showing how landscapes evolve through time.
Their results indicate that when Rodinia was fragmenting, the future Grand Canyon sat in roughly the same position relative to the continental edge as major escarpments found today in places such as South Africa and Brazil.
Over tens of millions of years, the giant cliff system would have gradually migrated inland as erosion wore it down. The researchers estimate that this process could have removed as much as eight kilometers of rock in some locations.
That prediction agrees with other geological evidence showing that roughly five to ten kilometers of rock disappeared from parts of the region long before the modern Grand Canyon formed.
“This long-lived tectonic landscape provides a missing piece in understanding why erosion associated with the Great Unconformity varies so dramatically across the southwestern US,” said Prof Gernon.
He added: “Our work suggests that tectonic uplift related to continental rifting and breakup created both steep slopes and high ground, providing the mountainous terrain that rivers and glaciers could readily erode.”
An Ancient Mountain Rim That Reshaped North America
The influence of this enormous escarpment may have extended far beyond the area that eventually became the Grand Canyon.
By producing a long-lived mountainous rim around western Laurentia — the ancient core of North America — the landscape may have shaped the paths of rivers, determined where sediments collected, and influenced when rising seas spread across the continent before the so-called Cambrian explosion, a period when complex life diversified rapidly.
Prof Gernon added: “Today’s escarpments in Africa, Brazil, India and Antarctica provide windows into the forces that shape continents over hundreds of millions of years.
“By comparing Grand Canyon’s ancient history with active landscapes like the Great Escarpment of South Africa, we’re able to see North America’s most iconic geologic landmark in an entirely new light.
“Our findings could help geologists reinterpret other ancient continental interiors where similarly large gaps occur in records, offering a better understanding of how Earth’s continents have changed over hundreds of millions of years.”
