Deep Inside Earth, Two Giant Hidden Structures May Be Steering the Planet’s Magnetic Field

Nearly 3,000 kilometres beneath us lie two enormous structures. These structures may be directly shaping Earth's vital magnetic field.

Scientists call these features Large Low-Shear-Velocity Provinces, or LLSVPs. Vast and continuous, these regions lie at the boundary between Earth’s solid mantle—the thick layer below the crust—and its liquid outer core, a molten metal layer beneath the mantle. One sits beneath Africa, the other under the Pacific Ocean. Each province spans thousands of kilometres, making it comparable in size to a continent.

Researchers detect these structures using seismic waves. These waves slow as they pass through hotter, chemically distinct regions deep inside Earth. Through seismic imaging, scientists reveal the shape and position of LLSVPs, highlighting their relevance to Earth's interior dynamics.


For years, scientists debated these formations. New research focuses on their direct influence on Earth’s magnetic field.

How the Magnetic Field Is Created



Earth’s magnetic field arises deep within our planet. In the outer core, molten iron and nickel churn turbulently as heat escapes into the cooler mantle above. As Earth spins, these moving currents twist into spirals.

Scientists name this process the geodynamo. It’s the churning, electrically conductive liquid metal in Earth's outer core that generates magnetic fields. Without this restless motion, Earth would lack its magnetic shield—the invisible force that protects us from harmful solar radiation and cosmic particles.

Heat flow is the key driver of this motion—increased core heat loss leads to more vigorous molten-iron circulation.

These giant mantle structures help determine how the magnetic field is generated and behaves.

Uneven Heat Flow Changes Everything

A recent study published in Nature Geoscience used paleomagnetic records—ancient evidence of Earth’s magnetic field stored in rocks—and advanced computer simulations to examine how temperature differences at the core-mantle boundary change magnetic behavior.

The researchers determined that LLSVPs are hotter than the surrounding mantle; because of their increased warmth, they permit less heat to escape from the underlying core. In contrast, cooler areas enable heat to flow out more freely.

This uneven heat extraction (removal) influences how liquid iron circulates in the outer core. Including these large thermal anomalies—regions that are hotter or cooler—improves how simulations match the patterns of Earth’s magnetic field over time. Excluding these anomalies makes it impossible for the models to reproduce the magnetic field's long-term behaviour.

Thus, Earth’s magnetic field is shaped unevenly by the structures above the core.

Geomagnetism researcher Andy Biggin explains that beneath hotter mantle regions, liquid iron may move more slowly than in cooler mantle areas. Those variations in flow patterns influence the generation and structure of magnetic fields.

Geophysicist Paula Koelemeijer emphasises another point: mantle composition matters. Even if temperatures are alike, chemical differences can alter how heat transfers from the core. Models of deep Earth dynamics must account for these variations.

Clues Locked in Ancient Rocks

How do scientists know what Earth’s magnetic field looked like millions of years ago?

When volcanic rocks cool at Earth’s surface, tiny magnetic minerals within them align with the planet’s magnetic field of that era. Once these rocks solidify, the alignment is locked in place. By analysing these paleomagnetic records—traces of past magnetic fields preserved in rocks—researchers can piece together the field's behaviour over hundreds of millions of years.

The study uncovered that specific long-term stability patterns in Earth’s magnetic field over the past 265 million years make the most sense if strong temperature contrasts at the core-mantle boundary persisted through that period. This finding suggests the two giant mantle structures have shaped the magnetic field for a truly extraordinary length of time.

Why This Matters Today

Earth’s magnetic field not only protects the atmosphere but also shields satellites, communication systems, and power grids from solar radiation. Although magnetic reversals and fluctuations are natural phenomena, understanding their drivers enables scientists to interpret long-term trends better.

The realisation that these structures affect the magnetic field changes our view of Earth’s interior. The planet's dynamic inner regions influence processes far beyond their immediate area.

What happens in Earth’s deep interior directly shapes the magnetic field that protects our world.

The ground beneath our feet may seem immovable. Still, deep below, colossal structures silently govern Earth’s magnetic fate—a force that has safeguarded our world for millions of years, and will help determine its future.