Hidden structures beneath Africa and the Pacific power Earth's magnetic shield

Two gigantic hot rock blobs deep inside Earth have been shaping our planet's magnetic field for ages, according to a new study.

The study was published in Nature Geoscience, and combines ancient magnetic records from rocks (palaeomagnetism) with supercomputer simulations.

WHAT ARE THESE BLOBS?

Earth's surface is made up of three layers. The crust, which is the planet's outermost layer; the mantle, which is a thick, semi-solid layer in the middle; and then there is the core, which is Earth's innermost layer divided into a liquid outer core and solid inner core.

Deep below the surface, about 2,900 kilometres down, at the boundary between the rocky mantle and the liquid outer core, sit two enormous structures.

One lies beneath Africa, the other under the Pacific Ocean.

These continent-sized blobs are made of solid, ultra-hot rock, surrounded by a ring of cooler material stretching from pole to pole.

Scientists call them Large Low Velocity Provinces because seismic waves slow down when passing through them, hinting at their extreme heat.

WHAT IS EARTH'S MAGNETIC FIELD?

Earth's magnetic field is like an invisible shield generated by swirling molten iron in the planet's outer core.

It acts as a giant bar magnet with north and south poles, protecting life from harmful solar wind and cosmic radiation.

Magnetic waves, often called geomagnetic waves or pulsations, are rapid fluctuations or ripples in this field caused by interactions between solar particles and Earth's magnetosphere, or by internal core-mantle dynamics.

These waves travel through space and the atmosphere, influencing everything from auroras to satellite operations and even animal navigation.

HOW DO BLOBS AFFECT MAGNETIC FIELDS?

Earth's protective magnetic field comes from the swirling liquid iron in the outer core, a process called the geodynamo.

It shows these hot blobs create strong temperature differences at the top of the core. Hot spots form right under the blobs, slowing or even stagnating the iron flow there.

In cooler areas, the flow stays vigorous.

Professor Andy Biggin, Professor of Geomagnetism at the University of Liverpool, explained: “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.

WHAT DOES IT MEAN FOR SCIENTIFIC HISTORY?

Looking back 265 million years, researchers found some parts of the field stayed stable for hundreds of millions of years, while others changed dramatically.

This challenges the long-held idea that Earth's field, averaged over long periods, acts like a simple bar magnet perfectly aligned with the planet's spin axis.

“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,” Biggin added.

He also noted the broader impact.

“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,” he said.

The findings point to an undeniable role of exploration and discovery that helps us understand the Earth better. It also highlights how there's a lot that we still don't know about our planet.

We've travelled billions of kilometres into space, yet the deepest we've drilled is just over 12 km.

These hidden blobs show how much remains unknown about our planet's interior, and how ancient rocks can unlock secrets about Earth's past, present, and future.