Mantle motion may explain Earth’s missing billion years

At the Grand Canyon and other sites, roughly 550-million-year-old sedimentary rock rests directly on basement rock more than a billion years older. The missing layers form the Great Unconformity, a widespread gap in Earth’s geological archive that precedes the Cambrian diversification of animal life. Competing explanations have emphasized Snowball Earth glaciers, rifting, sea-level fall and mantle plumes.

Santosh Dhungana and Nicolas Flament tested a deeper mechanism with global models of mantle convection and plate motion. Their simulations predict prolonged continental-scale uplift during the Neoproterozoic for Laurentia, Baltica and North China. Raised land was exposed to weathering and, during the Cryogenian ice ages, extensive glacial erosion. Later subsidence helped bury and preserve the eroded surface beneath younger sediments.

The model addresses both creation and survival of the gap. Laurentia—ancestral North America—was large and experienced comparatively limited deformation around its margins, so the erosional surface could remain unusually coherent. Cycles of predicted uplift and subsidence also broadly match changes in preserved sediment volumes across continents. The Great Unconformity is therefore interpreted as a surface record of slow mantle circulation, amplified by climate, rather than the scar of one simultaneous global stripping event.

This does not eliminate the other hypotheses. A numerical reconstruction is constrained by plate histories and geological observations but cannot directly replay erosion hundreds of millions of years ago. Glaciers still perform much of the proposed removal, while rifting and sea-level change can alter local records. The paper’s advance is to supply a dynamic process that produces the large-scale pattern those mechanisms must operate within.

The connection to the Cambrian explosion remains plausible rather than demonstrated. Erosion can deliver nutrients to oceans and subsidence can create sedimentary basins, changing marine environments before animal diversification. The study models landscape and sediment flux, not biological causation. Its strongest conclusion is narrower and substantial: some of the largest absences in the rock record may themselves be evidence of what the deep Earth was doing.