One of Earth’s deepest secrets has come to light in new University of Liverpool research that identifies how two vast, hot rock structures in the planet’s mantle produce unusual magnetic activity, shaping the planet over hundreds of millions of years.
What lies in the deepest regions beneath the Earth’s surface is fairly well understood, although humans have only directly observed it at a depth of 12 kilometers. Now, researchers have uncovered new evidence about the magnetic influence of two unusual structures where the Earth’s mantle touches the core, as revealed in a recent paper published in Nature Geoscience.
A Mysterious Boundary
A lack of direct access to Earth’s interior leaves room for uncertainty, as well as new discoveries. One such discovery was made recently when University of Liverpool researchers identified two continent-sized rock structures about 2,900 kilometers below Earth’s surface, located beneath Africa and the Pacific Ocean, that influence the planet’s magnetic field. These ultra-hot regions affect the planet’s molten outer core, altering how the magnetic field is generated locally.
According to the new study from the DEEP (Determining Earth Evolution using Palaeomagnetism) research group in the University of Liverpool’s School of Environmental Sciences, working with researchers from the University of Leeds, the rock forming these structures remains solid despite being superheated and is surrounded by a ring of cooler rock that stretches between the poles.
Investigating the Mantle
Similar to how a wind turbine generates electricity, the flow of liquid iron in Earth’s outer core produces the planet’s magnetic field. Inside Earth, the mantle acts as a cold sink for the geodynamo, creating cooler pockets. Although the mantle is relatively uniform seismically, researchers expect significant lateral variations in heat distribution, which could influence how the iron core flows. The DEEP team sought to use paleomagnetic data to better understand this region—a challenging task.
Previous work in this area assumed uniformity or examined relatively short time scales. In this study, the team combined magnetic data with a mathematical model of the geodynamo to investigate its activity over the last 265 million years. Collecting measurements of these magnetic fields and running simulations of the processes that generate them posed major technical challenges.
From the models, the team reconstructed 265 million years of magnetic field activity. The complexity and duration of these simulations pushed the limits of the supercomputers available to the researchers.
Mantle Structures Discovered
The simulations revealed an irregular upper boundary of the outer core. The immense rock structures capped the molten hot spots. Intriguingly, some areas of the magnetic field proved more volatile than others, either changing significantly or remaining relatively stable for hundreds of millions of years.
“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,” said lead author Andy Biggin, Professor of Geomagnetism at the University of Liverpool. “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,” Biggin added.
Overall, the team’s work challenges the assumption that the Earth’s magnetic field behaves like a stable bar magnet over long periods. From this new conceptual starting point, the team hopes that going forward, their findings will help the ancient processes that forged our modern planet come into clearer view.
The paper, “Mantle Heterogeneity Influenced Earth’s Ancient Magnetic Field,” appeared in Nature Geoscience on February 3, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.