Two massive hot rock formations buried 2,900 kilometers beneath Africa and the Pacific Ocean have been quietly steering Earth's magnetic field for millions of years. Scientists at the University of Liverpool just figured out how.
The discovery comes from an unusual combination: ancient magnetic records locked inside rocks, paired with supercomputer simulations of Earth's molten iron core. What emerged was a clearer picture of why some parts of our planet's magnetic shield have stayed rock-solid stable for hundreds of millions of years, while others have swung wildly.
How Deep Heat shapes the Field Above
Earth's magnetic field isn't generated by magic. It comes from liquid iron sloshing around in the outer core—essentially a natural dynamo, the way a wind turbine spins to create electricity. But that liquid iron doesn't move uniformly. The new research shows it's being shaped by what's happening directly above it: the temperature at the core-mantle boundary isn't evenly distributed.
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Start Your News DetoxBeneath those continent-sized hot rock structures, the liquid iron appears to stagnate—moving sluggishly compared to regions above cooler material. This uneven heating creates zones of vigorous flow and zones of relative stillness, and that patchwork directly influences which parts of the magnetic field stay consistent and which flip or wander.
"These findings suggest that there are strong temperature contrasts in the rocky mantle just above the core," explains Andy Biggin, Professor of Geomagnetism at Liverpool. "Beneath the hotter regions, the liquid iron in the core may stagnate rather than participate in the vigorous flow seen beneath the cooler regions."
The team, working within the university's DEEP research group (Determining Earth Evolution using Palaeomagnetism), spent years running simulations across 265 million years of Earth history. Even with supercomputer access, that's computationally brutal—but it allowed them to match their models against actual magnetic patterns preserved in ancient rocks collected from around the world.
The payoff: a working hypothesis for why Earth's magnetic personality is part stable, part changeable. And that matters beyond pure curiosity. Understanding how the deep Earth evolves over geological timescales helps us interpret what the magnetic record is actually telling us about our planet's interior dynamics.
The research opens a new angle on an old question: what drives the long-term behavior of Earth's magnetic field, and what does that tell us about the planet we live on.
