A 2026 study in Nature proposes that mantle-driven changes in continental elevation, working alongside glacial erosion, may help explain the Great Unconformity. Across six mantle-convection models, five produced a major uplift-then-subsidence cycle for Laurentia, the ancient continental core of North America. The study’s authors present this as a possible explanation, not a single established cause of the geological gap. (Nature)
The Great Unconformity is a break in the rock record where younger sedimentary rocks lie on much older rock, often crystalline basement. The gap reflects erosion, a pause in deposition, or both; its duration and expression vary by location.
How mantle motion could help create the gap
Earth’s mantle is solid rock that slowly deforms and circulates over geological time: hotter material rises and colder material sinks. That flow can shift broad areas of the surface upward or downward, a process called dynamic topography.
The study’s proposed sequence combines those gradual elevation changes with erosion. Broad uplift could expose rock, while glaciers during the Cryogenian glaciation, about 720–635 million years ago, could scour it. Later subsidence could allow sediment to cover the eroded surface and help preserve the boundary in the rock record.
Broad uplift can expose rock; glaciers can provide the erosive force that gentle slopes alone may lack.
The study separates formation from preservation
The researchers ran six CitcomS mantle-convection cases spanning the past billion years. They analyzed one window for the modeled formation of the unconformity and a later window for its preservation potential:
| Model phase | Analysis window | What the study examines |
| Formation | 920–420 million years ago | Modeled conditions associated with forming the unconformity |
| Preservation | 420 million years ago to the present | Modeled potential for preserving it |
These are the study’s analysis windows, not dates for one event shared by every region. The distinction matters because erosion may create a surface, while later subsidence and sediment burial may preserve it.
The regional results are not uniform
Five of the six model cases predict one main uplift-and-subsidence cycle for Laurentia; M3 is the exception. For Baltica and North China, Precambrian uplift appears in four of the six cases, with its modeled duration and magnitude varying.
That regional variation fits a geological record in which comparable-age unconformities occur in several continental regions but do not appear as one identical, equally exposed surface everywhere. Later tectonic histories also affect what remains visible: repeated mountain-building can complicate the record in places such as Baltica and North China.
The model’s strongest signal is the trend
The researchers favor model M1 based on its comparisons with present-day lower-mantle structure and reconstructed volcanic provinces. Five cases use a no-net-rotation reference frame; M3 uses a paleomagnetic frame. The tectonic reconstructions that guide the simulations become less certain farther back in time.
The model setup calculates dynamic topography from sources deeper than 350 kilometers, leaving out shallower sources. The authors also say this setup overpredicts long-wavelength topography’s amplitude by about a factor of two, so the modeled height is less dependable than the broad pattern of uplift followed by subsidence.
The study’s geological proposal does not establish mantle convection as the cause of the Cambrian explosion. It leaves any connection between the modeled geological processes and animal diversification as a possible environmental implication, rather than a causal finding.
