Scientists discover hidden deep-Earth structures shaping the magnetic field

That knowledge gap is especially important near the boundary between the mantle and the core. This region represents the most critical internal boundary within Earth and is now the focus of new research revealing unexpected magnetic behavior.

Giant Hot Rock Structures Beneath Africa and the Pacific

In a study published in Nature Geoscience, a research team led by the University of Liverpool found magnetic evidence that two massive, intensely hot rock formations at the base of Earth's mantle influence the liquid outer core beneath them. These structures sit about 2,900 kilometers below Africa and the Pacific Ocean.

The findings suggest that these enormous bodies of solid, superheated rock -- surrounded by a pole-to-pole ring of cooler material -- have played a role in shaping Earth's magnetic field for millions of years.

Combining Ancient Magnetism With Supercomputer Models

Reconstructing ancient magnetic fields and modeling the processes that generate them is extremely challenging. To investigate these deep-Earth features, the scientists combined palaeomagnetic data with advanced computer simulations of the geodynamo -- the movement of liquid iron in the outer core that produces Earth's magnetic field in a way similar to how a wind-turbine generates electricity.

These numerical models allowed the team to recreate key features of Earth's magnetic behavior over the past 265 million years. Even with access to a supercomputer, running simulations across such vast timescales requires immense computational effort.

Uneven Heat at the Core Mantle Boundary

The results showed that the upper boundary of the outer core does not have a uniform temperature. Instead, it contains sharp thermal contrasts, with localized hot zones sitting beneath the continent sized rock structures.

The analysis also revealed that some components of Earth's magnetic field have remained relatively stable for hundreds of millions of years, while other aspects have changed dramatically over time.

Andy Biggin, Professor of Geomagnetism at the University of Liverpool, said: "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.

"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 Pangaea -- and may help resolve long-standing uncertainties in ancient climate, palaeobiology, 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."

Research Team and Publication Details

The study was carried out by scientists from the DEEP (Determining Earth Evolution using Palaeomagnetism) research group within the University of Liverpool's School of Environmental Sciences, working alongside researchers from the University of Leeds.

Professor Biggin and his team focus on studying magnetic signals preserved in rocks collected from around the world to reconstruct the history of Earth's magnetic field and the planet's internal dynamics.

DEEP was established in 2017 with funding from the Leverhulme Trust and the Natural Environment Research Council (NERC).