Geologists Model Earth's Mantle Movements Over 1 Billion Years

Geologists have modeled movements in Earth’s mantle over the past billion years, suggesting that prolonged continental uplift combined with large-scale glaciation may have formed the Great Unconformity, a vast gap in the geological record. This phenomenon is particularly evident in the rocks of the Grand Canyon, where ancient crystalline rocks are overlain by Cambrian sandstones, with a potential geological history gap of 200 million to over 1 billion years, as reported by ua.news.

Mantle Convection Simulations

The study, published in the journal Nature by authors Nicolas Flament and Santosh Dungana, involved six simulations of mantle convection. In these models, hot masses of rock slowly rising in the mantle lifted parts of continents, while cold slabs of ocean floor sinking into the mantle at subduction zones contributed to surface subsidence. The amplitude of these vertical movements is estimated at several hundred meters, although its precise value remains debated.

The researchers noted that uplift alone was too gradual to destroy enough rock. They proposed that an additional factor may have been glacial erosion during the period around 720–635 million years ago, when glaciers reached the tropics. Flament stated that ice sheets erode rock about ten times more effectively than rivers. When continents subsided during the Cambrian period, seas flooded the eroded surface and covered it with new sediments.

Findings on Continental Movements

The models indicate that Laurentia, the ancient core of North America, underwent prolonged uplift between approximately 930 and 510 million years ago before beginning to subside during the Cambrian period. Five of the six simulations reproduced this sequence, while Northern Europe and Northern China appeared in four models. In contrast, calculations show that South America and Australia experienced two cycles each of uplift and subsidence, complicating the identification of a major unconformity there. The authors also noted uncertainty in the models’ initial configurations, as magnetic data can establish ancient continents’ distance from the equator but not their longitude. The team suggests that intense erosion may have carried rock material into the oceans shortly before the Cambrian explosion, when calcium became more widespread in seawater and life began forming skeletons and shells. Flament emphasized that mantle dynamics was only one of the processes contributing to these changes.