Mantle Motion Explains the Grand Canyon's Missing Billion Years

"We looked at, where are the best places that the mantle would help create a Great Unconformity?" study co-author Nicolas Flament, a geoscientist at the University of Wollongong in Australia, told Live Science. "And these three places turned out to be three places where it's known to be quite extensive."

The study references Dhungana, S., & Flament, N. (2026), "The deep Earth origin of the Great Unconformity," in Nature.

Wasn't it glaciers?

The cause of the Great Unconformity is hotly debated. One leading argument blames a global deep freeze known as Snowball Earth, which could have shoveled sediment off the continents as ice advanced and retreated. Glaciation probably played a major role in the erosion, Flament said. But the new study points to a deeper driver. Without the mantle pushing the continents up, glaciers and other erosive forces would have had no slope to push sediments down, he said.

Why does missing rock matter for life?

Earth constantly recycles its crust through plate tectonics, said Shanan Peters, a University of Wisconsin-Madison geologist who was not involved in the study. Oceanic crust sinks back into the mantle through subduction, when one tectonic plate dives beneath another, and its chemicals return to the atmosphere through volcanic eruptions.

That recycling changes chemistry over time. The ancient Paleo-Tethys ocean, which lapped the shores of the supercontinent Pangaea until it closed about 200 million years ago, carried carbon-rich sediments eroded from continents down into the deep planet. Today, most subduction happens around the Pacific Rim, where the seafloor sits far from continents and is relatively starved of carbon. The mantle is swallowing a different chemical mix now than it did 200 million years ago.

So calling the Great Unconformity "missing information" misses the point, Peters said. The absent rock record reveals what processes were running back then — and hints at how geology shaped the atmosphere, and with it, the evolution of life.

The geological churn may even have set the stage for the Cambrian explosion. Crystalline rocks exposed at the surface at that time may have released potassium, iron, manganese, and carbon into the seas at an increased rate, Peters said. Marine life may have responded by inventing biomineralization — shells — and the shifts may have made Earth's atmosphere more oxygen-rich.

"It contributes to the environment in which complex life evolved," Flament said.

Peters praised the study for explaining both sides of the phenomenon: the erosion and the switch back to deposition. "This seems to me to be the only reasonable way to go back and forth between this state over time," he said.

What's still uncertain?

Plenty, as with any model. Scientists still don't know everything the continents were doing during this stretch. Peters leads a project called Macrostrat that compiles observations of rock layers worldwide, and Flament hopes that database will ground-truth the new findings.

"So far in Africa and Russia, we don't have as comprehensive a database," Flament said. "Once that is done, we can go and check whether the idea works."

The takeaway: Earth's deep interior may have erased a billion years of rock history — and helped set the table for complex life in the process.