Two immense, ultrahot rock structures located at the base of Earth’s mantle, around 2,900 km beneath Africa and the Pacific, have been shaping Earth’s magnetic field for millions of years, according to a new study led by University of Liverpool’s Professor Andy Biggin.
Two enormous blobs of solid, superheated material located at the base of Earth’s mantle affect the underlying liquid outer core. Image credit: Biggin et al., doi: 10.1038/s41561-025-01910-1.
Both measuring ancient magnetic fields and simulating the processes that generate them are technically demanding.
To investigate these deep-Earth features, Professor Biggin and colleagues combined paleomagnetic observations with advanced computer simulations of the geodynamo — the flow of liquid iron in the outer core that generates Earth’s magnetic field like a wind-turbine generates electricity.
Numerical models enabled them to reconstruct key observations of the behaviour of the magnetic field seen over the past 265 million years.
Even with a supercomputer, running such simulations, especially over long timescales, represents an immense computational challenge.
The results revealed that the outer core’s upper boundary is far from uniform in temperature.
Instead, it displays strong thermal contrasts, with localized hot regions capped by the continent-sized rock structures.
It also showed that some parts of the magnetic field appear to have remained relatively stable for hundreds of millions of years, while others have changed significantly through time.
“These findings suggest that there are strong temperature contrasts in the rocky mantle just above the core and that, beneath the hotter regions, the liquid iron in the core may stagnate rather than participate in the vigorous flow seen beneath the cooler regions,” Professor Biggin said.
“Gaining such insights into the deep Earth on very long timescales strengthens the case for using records of the ancient magnetic field to understand both the dynamic evolution of the deep Earth and its more stable properties.”
“These findings also have important implications for questions surrounding ancient continental configurations — such as the formation and breakup of Pangea — and may help resolve long-standing uncertainties in ancient climate, paleobiology, and the formation of natural resources.”
“These areas have assumed that Earth’s magnetic field, when averaged over long periods, behaved as a perfect bar magnet aligned with the planet’s rotational axis.”
“Our findings are that this may not quite be true.”
The study was published today in the journal Nature Geoscience.
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A.J. Biggin et al. Mantle heterogeneity influenced Earth’s ancient magnetic field. Nat. Geosci, published online February 3, 2026; doi: 10.1038/s41561-025-01910-1
