A groundbreaking study published in Geophysical Research Letters has revealed that rocks deep within the Earth’s lower mantle can undergo dynamic transformations, carrying major implications for both earthquakes and the planet’s magnetic field. Nearly 2,900 kilometres below the surface, scientists detected a mysterious change at the core–mantle boundary using data from NASA and Germany’s GRACE satellites. In 2007, the satellites recorded a sudden gravitational anomaly, traced not to surface activity but to mass shifts deep inside the Earth. Researchers linked this to a mineral phase change that increased mantle density, subtly deforming the core boundary and coinciding with unusual magnetic field disturbances.
How GRACE satellites detected a deep Earth anomaly beneath the Atlantic
The GRACE mission (Gravity Recovery and Climate Experiment) involved two satellites flying in tandem from 2002 to 2017. Their main purpose was to track water movements across Earth, such as melting glaciers, shrinking aquifers, and rising seas. But the satellites were so precise that they could also detect subtle gravitational changes caused by shifts in mass deep within the planet. Think of them like two cars driving close together, if the road dips or rises, the distance between them changes. Similarly, when one satellite passed over an area with more mass, it was tugged slightly, altering its position relative to the other.In 2007, this sensitivity revealed something extraordinary: a gravitational anomaly beneath the Atlantic Ocean, off the coast of Africa. The signal was far too deep and powerful to come from surface events like rainfall or ice melt. Instead, it pointed to a disturbance within the solid Earth itself, right near the mantle–core boundary.
The 10-centimetre change that disturbed Earth’s core dynamics
At the boundary between the lower mantle and the outer core, rocks exist under unimaginable pressure and heat. Scientists believe that around 2007, something remarkable took place:Minerals such as perovskite underwent a phase change – their atomic structure collapsed into a denser form.This transformation increased the density and mass of a huge section of the mantle.The shift triggered a domino effect, causing nearby rocks to adjust and slightly deform the mantle–core boundary, by perhaps 10 centimetres.Though this might sound tiny, such a change at planetary scale is enough to disturb convection in the molten iron outer core. This, in turn, can affect the Earth’s magnetic field.
Link between gravity and magnetism
Interestingly, satellites tracking Earth’s magnetic field also recorded an unusual disturbance in the same region and time period.The gravitational anomaly and magnetic anomaly coincided around 2007.This suggests both were linked to the same deep geological event.Scientists now believe these processes could explain how changes inside Earth ripple outward, influencing both gravity and magnetism.This is a rare opportunity: for the first time, researchers have evidence that the deep mantle evolves dynamically, and fast enough to be studied in real time.Also read | NASA’s James Webb Telescope reveals supermassive black holes forming far earlier than expected, raising questions about primordial origins