Secrets of Earth's Buried Supercontinents Revealed

Two enormous, supercontinent-sized 'islands' buried deep within the mantle have been revealed to have fundamental differences—contrary to previous assumptions—and they may even lead to Earth's magnetic field becoming unstable.

This is the conclusion of an international team of researchers from the U.K. and U.S., whose modeling revealed that the two so-called Large Low-Velocity Provinces (LLVPs) have evolved differently, giving them different chemical compositions and densities.

Each up to 559 miles tall and thousands of miles wide—and together covering some 25 percent of the surface of our planet's core— Earth's LLVPs were first discovered in the 1980s, when geologists found that seismic waves were travelling much slower through two regions in the lower mantle than expected.

Scientists believe that the LLVPs are made up of accumulated oceanic crust subducted down into the mantle. Because seismic waves appear to travel through them in similar ways, it was long assumed that they had similar physical properties.

However, the new study has revealed that while they do have similar temperatures (that being the dominant control on how fast seismic waves pass through a material), they are made up of different compositions and ages of material.

"The fact that these two LLVPs differ in composition, but not in temperature is key to the story and explains why they appear to be the same seismically," paper author and seismologist professor Paula Koelemeijer of the University of Oxford said in a statement.

"It is also fascinating to see the links between the movements of plates on the Earth's surface and structures 3,000 kilometers [1,864 miles] deep in our planet."

In their study, Koelemeijer and her colleagues modeled how the LLVPs formed and evolved through time by combining a model of mantle convection with a reconstruction of the last billion years of tectonic plate movements across Earth's surface.

The simulation revealed that the African LLVP is made up of older material and is better mixed than its Pacific counterpart, which contains 50 percent more ocean crust subducted within the last 1.2 billion years.

Moreover, the models indicate that the Pacific LLVP has been being consistently refreshed by newly subducted oceanic crust for the last 300 million years.

This is because this LLVP is surrounded at the Earth's surface by the subduction zones responsible for the Ring of Fire, the 25,000-mile-long belt of volcanoes and areas of seismic activity that surrounds the Pacific Ocean.

"As numerical simulations are not perfect, we have run multiple models for a range of parameters," paper co-author and geodynamicist James Panton of Cardiff University, Wales, explained in a statement. "Each time, we find the Pacific LLVP to be enriched in subducted oceanic crust, implying that Earth's recent subduction history is driving this difference."

In contrast, the African LLVP does not seem to be receiving new material at the same rate—meaning that it has mixed more with the surrounding mantle, lowering its density.

The resulting differences in density between the two bodies could explain why the African LLVP is more spread out and taller than the one under the Pacific.

The difference in the two LLVPs could have significant ramifications, the researchers noted.

Because of their high temperatures and positions in the deep mantle on opposite sides of the Earth, the LLVPs affect how heat leaves the Earth's core.

"Heat extraction from the core will occur primarily where the overlying mantle is colder," Koelemeijer told Newsweek.

"The LLVP are thus the locations where less heat is extracted from the core."

This, in turn, affects convection in the outer core—the dynamo-like process that generates the magnetic field that protects life on Earth from harmful cosmic rays.

"Flow in the outer core drives the geodynamo that sustains the magnetic field. This flow is aligned with the Earth's rotation axis and influenced by how the heat is extracted from the core," Koelemeijer added.

"If the heat extraction becomes less symmetric, this is thought to lead to a magnetic field reversal."

A reversal would see the geomagnetic field temporarily weaken—and might also impact communications, power grids and the navigational abilities of certain animals.

The impact of the density imbalance, the team explained, will need to be factored into models of the deep Earth to determine if it might lead to an unstable geomagnetic field.

"We now need to look for data that can constrain the proposed asymmetry in density, for example using observations of Earth's gravitational field," Koelemeijer concluded.

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Update 04/02/25, 11:57 a.m. ET: This article was updated with additional information and comments from Paula Koelemeijer.

Reference

Panton, J., Davies, J. H., Koelemeijer, P., Myhill, R., & Ritsema, J. (2025). Unique composition and evolutionary histories of large low velocity provinces. Scientific Reports, 15(1), 4466. https://doi.org/10.1038/s41598-025-88931-3