Gravity often feels dependable and unchanging. It seems steady enough that we rarely question it. But the real picture is more surprising.
In reality, gravity does not have exactly the same strength everywhere on Earth. Its pull varies slightly across the planet’s surface. After accounting for the effects of Earth’s rotation, the weakest gravity is found beneath Antarctica.
Deep Earth Movements Created Antarctica’s Gravity Hole
A new study shows that extremely slow shifts of rock deep inside the planet helped produce the gravity anomaly beneath Antarctica. These movements occurred over tens of millions of years and gradually formed what scientists call the Antarctic gravity hole. The research also points out that changes in this gravity low happened during the same period as major shifts in Antarctica’s climate. Future studies may reveal whether these gravity changes helped encourage the development of the continent’s vast ice sheets.
“If we can better understand how Earth’s interior shapes gravity and sea levels, we gain insight into factors that may matter for the growth and stability of large ice sheets,” said Alessandro Forte, Ph.D., a professor of geophysics at the University of Florida and co-author of the new study recreating the Antarctic gravity hole’s past.
The differences in gravity come from variations in the density of rocks far beneath Earth’s surface. While the changes in gravitational strength are small, they can influence the oceans in noticeable ways. In regions where gravity is weaker, seawater tends to flow toward areas where the pull is stronger. As a result, the ocean surface in those weaker gravity zones sits slightly lower relative to Earth’s center. Because of the gravity hole beneath Antarctica, sea-surface height around the continent is measurably lower than it would otherwise be.
Using Earthquakes to Map the Planet’s Interior
The research, published recently in Scientific Reports, was conducted by Forte and Petar Glišović, Ph.D., of the Paris Institute of Earth Physics. The scientists mapped the Antarctic gravity hole and reconstructed how it evolved over millions of years. Their work relied on a global scientific effort that combined earthquake recordings from around the world with physics-based computer models. Together, these tools helped reveal the three dimensional structure hidden inside Earth.
“Imagine doing a CT scan of the whole Earth, but we don’t have X-rays like we do in a medical office. We have earthquakes. Earthquake waves provide the ‘light’ that illuminates the interior of the planet,” Forte said.
By analyzing how earthquake waves traveled through the planet and combining those data with physics-based modeling, the researchers created a detailed gravitational map of Earth. The results closely matched highly accurate satellite measurements of Earth’s gravity field. This agreement helped confirm that their models realistically captured the planet’s internal structure.
Rewinding Earth’s Geological History
The next step involved looking back in time to understand how the gravity hole developed. Using advanced computer simulations, the scientists reversed the slow movement of rocks inside the planet. Their models traced these changes back roughly 70 million years, to the era of the dinosaurs.
These reconstructed snapshots showed that the Antarctic gravity hole was initially weaker. Between about 50 and 30 million years ago, however, the anomaly began to grow stronger. That period coincides with major changes in Antarctica’s climate system, including the beginning of widespread glaciation.
Looking ahead, Forte hopes to explore whether the strengthening gravity anomaly played a role in shaping Antarctica’s ice sheets. Future models will examine how gravity, sea level, and changes in continental elevation interact.
Ultimately, the researchers want to answer a larger question about Earth’s systems. As Forte explained, the goal is to understand “How does our climate connect to what’s going on inside our planet?”
