A team of geologists has found for the first time evidence that two ancient, continent-sized, ultrahot structures hidden beneath the Earth have shaped the planet’s magnetic field for the past 265 million years.
These two masses, known as large low-shear-velocity provinces (LLSVPs), are part of the catalog of the planet’s most enormous and enigmatic objects. Current estimates calculate that each one is comparable in size to the African continent, although they remain buried at a depth of 2,900 kilometers.
Low-lying surface vertical velocity (LLVV) regions form irregular areas of the Earth’s mantle, not defined blocks of rock or metal as one might imagine. Within them, the mantle material is hotter, denser, and chemically different from the surrounding material. They are also notable because a “ring” of cooler material surrounds them, where seismic waves travel faster.
Geologists had suspected these anomalies existed since the late 1970s and were able to confirm them two decades later. After another 10 years of research, they now point to them directly as structures capable of modifying Earth’s magnetic field.
LLSVPs Alter the Behavior of the Nucleus
According to a study published this week in Nature Geoscience and led by researchers at the University of Liverpool, temperature differences between LLSVPs and the surrounding mantle material alter the way liquid iron flows in the core. This movement of iron is responsible for generating Earth’s magnetic field.
Taken together, the cold and ultrahot zones of the mantle accelerate or slow the flow of liquid iron depending on the region, creating an asymmetry. This inequality contributes to the magnetic field taking on the irregular shape we observe today.
The team analyzed the available mantle evidence and ran simulations on supercomputers. They compared how the magnetic field should look if the mantle were uniform versus how it behaves when it includes these heterogeneous regions with structures. They then contrasted both scenarios with real magnetic field data. Only the model that incorporated the LLSVPs reproduced the same irregularities, tilts, and patterns that are currently observed.
The geodynamo simulations also revealed that some parts of the magnetic field have remained relatively stable for hundreds of millions of years, while others have changed remarkably.
“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, paleobiology, and the formation of natural resources,” said Andy Biggin, first author of the study and professor of Geomagnetism at the University of Liverpool, in a press release.
“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 added.
This story originally appeared in WIRED en Español and has been translated from Spanish.