"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."
Two continent-sized, ultrahot masses called large low-shear-velocity provinces (LLSVPs) lie buried about 2,900 kilometers beneath the surface and are comparable in size to the African continent. Surrounding each LLSVP is a ring of cooler material where seismic waves travel faster. The hotter, denser, and chemically distinct mantle within LLSVPs affects heat and flow patterns at the core-mantle boundary. Temperature contrasts between LLSVPs and surrounding mantle alter liquid iron circulation in the outer core, producing asymmetric flow. That asymmetry changes how the dynamo generates the magnetic field. Simulations comparing uniform and heterogeneous mantle models reproduce the observed magnetic-field irregularities.
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