A frozen continent at the bottom of the world sits over the deepest dip in Earth’s gravitational pull, a feature that has persisted for roughly 70 million years. Scientists have long known about this anomaly, but a new study finally explains why it exists, pointing to slow-churning forces deep in the planet’s mantle rather than ancient asteroid impacts or hidden geological oddities.
What the Antarctic Geoid Low Actually Is
Earth’s gravity is not uniform. The planet’s uneven distribution of mass, from mountain ranges to ocean trenches to density variations deep underground, means gravitational pull shifts subtly from place to place. When scientists map these variations onto a theoretical surface called the geoid, they find highs and lows that reflect where mass concentrates or thins out. The most extreme low point on this map, known as the Antarctic geoid low, sits over the Ross Sea and Ross Embayment region of Antarctica. In practical terms, this means the gravitational tug in that area is weaker than almost anywhere else on the planet’s surface, forming a broad depression in the global gravity field rather than a literal hole in the ice or rock.
Alessandro Forte, Ph.D., a professor of geophysics at the University of Florida, has framed the phenomenon in accessible terms. “Gravity varies over the Earth’s surface,” Forte explained, emphasizing that the variation reflects the three-dimensional structure inside Earth more than surface-level features like ice sheets or topography. The geoid low is not a physical void but a region where less-dense material below the surface reduces the local gravitational field. That subtle weakening, invisible to human senses, can nonetheless be mapped with remarkable precision by satellites designed to track minute changes in Earth’s gravitational pull.
Seventy Million Years of Mantle Dynamics
The new study, published in Scientific Reports by Springer Nature, traces the Antarctic geoid low’s history back approximately 70 million years, well into the late Cretaceous period when dinosaurs still roamed. By reconstructing past plate motions and simulating mantle flow, the authors show that long-wavelength convection currents in the mantle (vast loops of hot rock rising and cooler rock sinking over tens of millions of years) have sustained a low-density zone beneath the Ross Embayment. As lighter, warmer mantle material wells upward, it displaces denser rock, subtly reducing the gravitational pull above. The persistence of this upwelling explains why the geoid low has remained anchored in roughly the same place despite the slow rearrangement of continents and ocean basins.
This finding carries broader implications for how scientists understand planetary interiors. If a single gravity anomaly can remain stable for 70 million years, it suggests that deep mantle flow patterns are far more coherent and long-lived than some models have assumed. The Antarctic geoid low is not a fleeting ripple in the planet’s gravitational field. It is a durable fingerprint of convection that has outlasted continental drift, mass extinctions, and dramatic climate shifts. For researchers studying how Earth’s interior influences surface conditions, from volcanic activity to tectonic plate motion, the longevity of this feature offers a rare fixed reference point in an otherwise dynamic system, helping to test competing models of mantle structure and evolution.
How GRACE Satellites Measured the Invisible
Untangling the Antarctic gravity puzzle would have been impossible without satellite missions dedicated to weighing the planet from orbit. NASA’s Gravity Recovery and Climate Experiment, known as GRACE, and its successor, GRACE-FO, fly twin spacecraft in tandem, tracking tiny changes in the distance between them as they pass over regions of slightly stronger or weaker gravity. These measurements are processed into monthly gravity field solutions, including the CSR Release 06.3 data distributed by NASA’s Physical Oceanography Distributed Active Archive Center. From these solutions, scientists compute geoid undulations, revealing where the gravity field bulges or dips relative to an idealized, perfectly smooth Earth.
In those maps, the Antarctic geoid low stands out as a broad, coherent depression spanning the Ross Sea region, distinct from smaller, sharper anomalies elsewhere on the continent. GRACE observations have also highlighted other Antarctic gravity features that can be easily confused with the geoid low but arise from very different processes. A prominent mass concentration under East Antarctica, for example, reflects an excess of dense material in the crust or upper mantle rather than a deficit. Interpreting such signals correctly requires careful modeling of ice thickness, bedrock topography, and mantle structure, because a mascon and a geoid low are effectively opposite signatures: one marks extra mass, the other marks missing mass.
The Wilkes Land Impact Theory and Why It Falls Short
For years, one of the most attention-grabbing explanations for Antarctic gravity anomalies centered on a possible ancient impact crater buried beneath Wilkes Land. Early analyses of GRACE-derived free-air gravity data, summarized in a NASA technical report, identified a circular positive anomaly consistent with a mascon in North Central Wilkes Land. Later studies combined those gravity observations with subglacial terrain maps and satellite magnetic measurements from missions such as Magsat and CHAMP to strengthen the impact-basin interpretation, arguing that a giant asteroid collision could have left behind a dense plug of material that still perturbs Earth’s gravity field today. The idea of a hidden mega-impact beneath the ice proved irresistible to headline writers and captured public imagination.
However, the Wilkes Land mascon and the Antarctic geoid low are geographically and physically separate phenomena. The Wilkes feature is a localized gravity high, while the Ross Sea anomaly is a broad gravity low tied to reduced density in the underlying mantle. The new modeling work in Scientific Reports makes this distinction explicit: the 70-million-year persistence and large spatial scale of the Ross Sea depression align much more closely with deep thermal convection than with a near-surface impact scar. Alternative explanations, including the possibility that dense materials from various geologic processes could account for certain anomalies, have been considered for specific regions. Yet none of those scenarios reproduces the amplitude, shape, and longevity of the Antarctic geoid low as convincingly as the mantle-flow model, which naturally links the gravity signal to the slow circulation of rock thousands of kilometers below the surface.
Why the Explanation Matters Beyond Antarctica
Resolving the origin of the Antarctic geoid low does more than tidy up a geophysical curiosity; it strengthens a broader framework for using gravity to read Earth’s interior. By tying a prominent anomaly to long-lived mantle convection, the study shows how gravity data can be integrated with seismic tomography, plate reconstructions, and numerical modeling to reconstruct the planet’s thermal and compositional structure through deep time. That same toolkit can be applied to other enigmatic gravity features around the globe, offering clues about how supercontinents assembled and broke apart, where mantle plumes rise toward the surface, and how heat flow from below influences the evolution of ice sheets and oceans.
The research also underscores the value of sustained satellite observations and open data systems. Products like GRACE-FO’s monthly gravity fields, technical analyses preserved in the NASA Technical Reports Server, and direct communication channels such as NASA’s scientific information office give researchers worldwide the tools to revisit old hypotheses and test new ones as models improve. In the case of Antarctica, those resources have helped shift the narrative from speculative impact craters toward a more comprehensive picture of deep Earth dynamics. Far from being an isolated oddity, the Antarctic geoid low now stands as a benchmark for how subtle signals in gravity can illuminate processes unfolding far beneath our feet, on timescales that stretch across much of Earth’s history.
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*This article was researched with the help of AI, with human editors creating the final content.
