Earth is not just a perfect sphere; its gravity fields are more like a bumpy potato. One of the most significant bumps—or rather, a dip—in this gravitational field is found under Antarctica. New research shows that this depression, known as the Antarctic Geoid Low, is becoming stronger over time. This change is driven by deep movements of rock beneath the Earth’s crust, almost like the planet is shifting in its sleep.
Geophysicist Alessandro Forte from the University of Florida explains that understanding how Earth’s inner layers influence gravity is important for studying large ice sheets. The uneven shape of Earth’s gravitational field is linked to how mass is distributed inside the planet. Different rocks have varying densities. This uneven distribution leads to the unique bumpy shape of the Earth.
When you stand on a geoid low or a geoid high, you probably wouldn’t notice much difference in your weight—only a few grams. But this subtle change gets us closer to understanding processes happening far beneath the surface.
Forte and Petar Glišović, a geophysicist from the Paris Institute of Earth Physics, used seismic waves from earthquakes to map the Antarctic Geoid Low. These waves shift speed and direction depending on the materials they pass through—much like a CT scan revealing the inner workings of a body, but instead, for the Earth.
Using this earthquake data, the researchers created a detailed 3D model of Earth’s mantle and compared it to satellite data. The results were impressive, validating their model against existing gravity measurements.
The next challenge was to trace the history of this geoid low back to 70 million years ago. They used their map to simulate how the Earth’s interior has evolved over that time, revealing that this depression has been present for millions of years but hasn’t remained unchanged. About 50 million years ago, it began to move and strengthen, coinciding with a significant shift in Earth’s rotational axis.
This shift was partly due to tectonic plates sinking beneath Antarctica, which altered the gravity field and enhanced the gravitational low. A rise in hot, buoyant materials has also contributed to the geoid’s evolution over the past 40 million years, intensifying this anomaly.
Interestingly, researchers speculate this process may relate to the significant glaciation in Antarctica that began around 34 million years ago. As the geoid depression deepened, it could have influenced local sea levels, possibly impacting the growth of the ice sheet. While this hypothesis needs more investigation, it highlights an important connection between geological movements and climate changes.
The gravity anomaly under Antarctica serves as a reminder that even the slowest geological movements can have lasting impacts on our planet. This research was published in Scientific Reports.
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