Earth may appear nearly spherical, but its gravitational field tells a different story. Instead of a smooth shell, Earth’s gravity resembles a lumpy potato, shaped by uneven mass distribution deep inside the planet. One of the most striking features of this distorted field is the Antarctic Geoid Low—a broad depression beneath Antarctica where gravity is slightly weaker. New research shows this anomaly is not only ancient but continues to intensify, driven by slow, powerful movements within Earth’s mantle.
Geophysicist Alessandro Forte of the University of Florida, together with colleague Petar Glišović of the Institut de Physique du Globe de Paris, set out to understand how this feature evolved over tens of millions of years. Their work begins with the realization that gravity reflects mass: where rocks are denser, the gravitational pull is slightly stronger; where lighter or hotter material dominates, it weakens. Although these differences are far too small for people to feel—amounting to only a few grams on a scale—they provide a powerful window into Earth’s hidden interior.
To peer beneath Antarctica, the researchers used seismic waves generated by earthquakes. As these waves pass through the planet, they speed up or slow down depending on the materials they encounter. By analyzing this behavior, Forte and Glišović created a detailed three-dimensional map of mantle density—essentially a CT scan of the entire Earth. From this model, they reconstructed the global geoid and compared it with satellite measurements of gravity, finding an impressive match.
The team then pushed their analysis further by rewinding Earth’s interior dynamics back 70 million years to the early Cenozoic. Using physics-based simulations of mantle convection, they tracked how shifting tectonic plates and circulating hot rock reshaped the geoid over time. When they let the model run forward again, it successfully reproduced today’s geoid and even matched observed changes in Earth’s rotational axis, known as True Polar Wander. This agreement suggests their reconstruction captures real processes operating deep within the planet.
The results reveal that a gravitational depression has lingered near Antarctica for at least 70 million years, but its strength and position have evolved. Around 50 million years ago, the anomaly began changing rapidly, coinciding with a sharp shift in polar wander. The model indicates that sinking tectonic slabs beneath Antarctica altered the surface expression of gravity, while a rising plume of warm, buoyant mantle material has increasingly amplified the geoid low over the past 40 million years.
Intriguingly, this deep-Earth evolution may be linked to Antarctica’s glaciation, which accelerated about 34 million years ago. Because the geoid influences sea level, a downward shift in the geoid around Antarctica would have lowered the local ocean surface, potentially helping ice sheets expand. While this connection remains speculative, it highlights how mantle convection, pole motion, sea level, and ice growth may all be intertwined.
Ultimately, the subtle gravity hole beneath Antarctica serves as a reminder that even the slowest geological processes can shape surface environments over geological time. What happens deep inside Earth does not stay there—it leaves lasting fingerprints on oceans, ice sheets, and the planet we experience today.