Hidden Mantle Giants May Have Shaped Earth’s Magnetic Field for Hundreds of Millions of Years

Scientists have uncovered new evidence that two vast, ancient structures buried deep within the Earth’s mantle have influenced the planet’s magnetic field for more than 260 million years, according to new research published in Nature Geoscience.

The continent-sized formations, known as large low-shear-velocity provinces (LLSVPs), lie nearly 2,900 kilometers beneath the Earth’s surface, close to the boundary between the mantle and the core. Though invisible from above, researchers say these massive regions have played a key role in shaping how Earth’s magnetic field behaves over geological time.

An illustration shows two massive low-shear-velocity provinces deep within Earth’s mantle near the core–mantle boundary.

Rather than being solid blocks, the LLSVPs are irregular zones where mantle material is significantly hotter, denser and chemically distinct from surrounding regions. Each is encircled by cooler material that allows seismic waves to travel faster, a feature that has helped scientists map their presence deep underground.

Researchers have debated the influence of these structures for decades. In the latest study, a team led by geologists at the University of Liverpool linked the LLSVPs directly to changes in the flow of liquid iron within Earth’s outer core — the process that generates the planet’s magnetic field.

Using supercomputer simulations, the scientists compared how the magnetic field would evolve in a uniform mantle with how it behaves when temperature and density differences from the LLSVPs are introduced. Only the models that included these deep-mantle anomalies reproduced the uneven patterns, tilts and long-term stability seen in real magnetic field data.

The findings suggest that while some portions of Earth’s magnetic field have remained stable for hundreds of millions of years, others have shifted dramatically, influenced by the contrasting hot and cold regions deep below the surface.

Lead author Andy Biggin, a professor of geomagnetism at the University of Liverpool, said the research could also shed light on broader geological puzzles, including the assembly and breakup of the supercontinent Pangaea, ancient climate patterns, and the formation of natural resources.

The study challenges the long-held assumption that Earth’s magnetic field behaves like a perfectly aligned bar magnet when averaged over long timescales, suggesting instead that deep-Earth structures have introduced persistent irregularities throughout the planet’s history.