Ancient magnetic records have shown that two vast, overheated regions deep inside Earth have guided the planet’s magnetic field for hundreds of millions of years.
The research reveals that Earth’s magnetic field has been steered by the same deep features for an extremely long time.
Magnetic clues in rocks
The magnetic imprint emerges from rock records that preserve how Earth’s field behaved while continents drifted and oceans opened.
By tracing those signals across hundreds of millions of years, researchers at the University of Liverpool (UoL) documented a persistent influence tied to Earth’s deepest interior.
The work was led by Professor Andy Biggin, a specialist in ancient magnetic fields.
The team found that those signals show that the field did not simply wobble randomly but retained stable features linked to where heat accumulated far below the surface.
That persistence sets limits on how Earth’s magnetic history can be interpreted and opens the door to examining what drives those long-lived patterns.
Deep hot regions
Seismic maps show two continent-sized regions of unusually hot rock about 1,800 miles down, near where the mantle meets the outer core.
Scientists build those maps from earthquake waves, and slower waves usually point to hotter rock or unusual chemistry.
A 2008 paper described deep provinces under Africa and the Pacific and argued that they could persist for ages.
If those hot provinces really stay put, they can keep feeding the core an uneven pattern of heat.
Heat drives magnetism
Heat moving out of the core keeps liquid iron in motion, and that motion builds the magnetic field around Earth.
Scientists call this engine the geodynamo, a self-sustaining flow that makes magnetism and slowly wanders over time.
Cooler mantle patches pull more heat upward, while hotter patches reduce heat loss and damp the core’s churning.
When that imbalance lasts for millions of years, the magnetic field can keep a built-in tilt instead of averaging out.
Rocks that hold a record
Many volcanic rocks locked in a compass direction as they cooled, leaving a time-stamped record of past field behavior.
Scientists read that record with paleomagnetism, measuring ancient magnetism preserved in minerals, then compare sites across many continents.
“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,” said Biggin.
Because rocks form in patches and get altered, the record stays uneven, and the team had to choose carefully.
Testing Earth inside computers
To test whether mantle heat could steer magnetism, the researchers ran core simulations that recreated patterns seen in ancient rocks.
They tuned the models to match field behavior across 265 million years, a span long enough to cover supercontinent drama.
Even on a supercomputer, long runs cost serious time, so the UoL team looked for the most stable signals first.
Those choices let them link specific field quirks to specific boundary temperatures, rather than blaming random turbulence.
Magnetic patterns remained steady
Across those long histories, the team found that some magnetic features stayed steady for hundreds of millions of years.
Other features drifted, weakened, or strengthened, showing that the field can hold structure without freezing in place.
In the simulations, persistent heat contrasts broke the usual symmetry, creating regional bends in field direction by more than 10 degrees.
That scale of bend can mislead anyone treating the time-averaged field as perfectly aligned with Earth’s rotation axis.
Magnetic bias affects ancient maps
Geologists use ancient field directions to place continents on maps, especially when rocks predate the oldest seafloor.
That method assumes the long-term field points along the spin axis, so latitude estimates stay clean and comparable.
If deep mantle heat skews the field in certain longitudes, reconstructions of Pangaea’s assembly and breakup can drift.
The new work suggests some long-running disputes may come from magnetism itself, not only from missing rocks.
Surface impacts of mapping errors
When continental maps drift, climate reconstructions drift too, because latitude controls sunlight, ice, and the kinds of ecosystems that thrive.
Researchers also use deep-time maps to track where sediments formed and where fluids moved, which matters for many resources.
Biggin’s team did not claim to rewrite every ancient map, but their result adds a new correction step.
Better rock coverage and clearer models will decide which time periods show real bias, and which only look messy.
Future research directions
More volcanic sampling at low latitudes would tighten the ancient record and reduce the guesswork in long-term averages.
Seismologists can also look for signs that the uppermost core holds persistent patches of slowed flow under the hot provinces.
On the computing side, faster machines will let models test more settings, including how chemistry changes heat movement.
If future work confirms the pattern, Earth’s magnetic history becomes a tool for mapping deep structure, not just pole flips.
The study links magnetic signals preserved in surface rocks to long-lived heat patterns deep inside Earth, bringing together seismology, geology, and core physics.
As more rock records are collected and models improve, that connection could refine ancient maps without assuming Earth’s magnetic field was perfectly simple.
The study is published in the journal Nature Geoscience.
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