Antarctica hides many mysteries, but one of the strangest is a giant "gravity hole" under the ice.
Gravity may seem constant everywhere, but its strength varies over the Earth's surface. In areas where gravity is weaker, ocean water can drop significantly below average, drifting toward areas with stronger gravity.
Scientists have known for years that gravity is weaker in a part of Antarctica's Ross Sea, where sea level drops 420 feet (about 130 m) below the surrounding water. Now, a group of researchers claim to have finally discovered the reason.
This huge hole, called the Antarctic Geoid Low (AGL), is the result of extremely slow rock movements. Initially 70 million years ago – when dinosaurs still ruled the Earth – lower-density rocks piled up under the frozen continent and weakened the pull of gravity.
The crater started small and then grew in strength between 50 and 30 million years ago, creating the ocean displacement we see today.
When astronauts look at Earth from the International Space Station, it may look like a smooth blue ball, but in reality, our planet is shaped like a “squiggly potato.” This uneven surface comes from areas of different gravity, caused by the uneven distribution of materials beneath the surface.
In areas where warm rock from the Earth's mantle rises toward the surface, the rock's lower density means gravity is weaker. Since the 1940s, researchers have known that these gravitational anomalies create deep depressions in the ocean. But understanding how and why they form hundreds of miles below the surface has been much more difficult.
To map the formation of the Antarctic gravity well, researchers combined earthquake records from around the world with a computer model of the Earth. Dr Alessandro Forte from the University of Florida explains: “It’s like taking a CT scan of the entire Earth, but we don’t have X-rays like in a medical clinic. We have earthquakes. Seismic waves are the ‘light’ that illuminates the interior of the planet.”
By analyzing how earthquakes travel through rocks of different densities, the researchers created a map of the Earth's interior. Then, with computer modeling, they predicted where gravity would be strongest or weakest based on rock types.
When the predictions matched the best satellite data, they turned back time and watched the gravity well form over millions of years. The gravity well formed slowly at first and then strengthened during the Eocene Epoch, about 50 million years ago – a time when Antarctica's climate was changing rapidly and glaciers were advancing rapidly.
Scientists suspect there may be a link between the formation of the gravity well and the continent's glaciers. Dr Forte says: "If we better understand how the Earth's interior affects gravity and sea levels, we gain insight into the factors that influence the growth and stability of large glaciers."
The Antarctic Trench is not the only large depression on Earth. In the Indian Ocean, the Indian Ocean Geoid Low has gravity so weak that the water drops 340 feet (103 m) below normal. Researchers in India say it was created by a low-density magma plume rising from the Earth's mantle, caused by the remains of a submerged tectonic plate, Tethys, when India collided with Asia 50 million years ago. /GazetaExpress/
t7 live
