Geologists have spotted a gravity hole in the Indian Ocean, something that has been puzzling them for a long time how and why it got there. A "gravity hole" is a spot where the Earth's gravitational pull is weaker, its mass lower than normal, and the sea level dipping by over 328 feet (100 meters).
A CNN report said researchers from the Indian Institute of Science in Bengaluru have found what they believed was a credible explanation for its formation, which are plumes of magma coming from deep inside the planet, which was similar to those that lead to the creation of volcanoes.
The researchers have been using supercomputers to simulate how the area could have been formed as an ancient ocean that no longer exists, with their hypothesis saying it could go as far back as 140 million years. The findings were detailed in a study recently published in the journal Geophysical Research Letters.
Earth Not as Round as We Think, Indian Geologists Say
According to Indian Institute of Science Centre for Earth Sciences associate professor Attreyee Ghosh, the Earth is a "lumpy potato" or an ellipsoid whose middle section is bulged outward as it rotates. He added the Earth is also not as homogeneous in density and properties, with some areas being more dense than others, which would affect the planet's surface and its gravity.
The Indian Ocean geoid low, as scientists called the "gravity hole", is the lowest point in the geoid, a part of the ocean floor that takes in more water than most parts of the Earth. Its biggest gravitational anomaly forms a circular depression that starts just off India's southern tip and covers about 1.2 million square miles (3 million square kilometers).
The anomaly was first discovered by Dutch geophysicist Felix Andries Vening Meinesz in 1948 as part of a gravity survey from a ship, which remained a mystery to this day.
The Fate of the Gravity Hole
"It is by far the biggest low in the geoid, and it hasn't been explained properly," Ghosh said.
When Ghosh and her team ran 19 computer model simulations to see the Earth and how it looked 140 million years ago, they discovered the formation of a geoid low similar to the one in the Indian Ocean in six of the scenarios. The distinguishing factor in all six of the models was the presence of plumes of magma around the geoid low, which along with mantle structure in the vicinity, were believed to be responsible for the formation of the "gravity hole," Ghosh explained.
The plumes themselves originated from the disappearance of an ancient ocean as India's landmass drifted and collided with Asia tens of millions of years ago. As the oceanic plate went down inside the mantle, the collision could have spurred the formation of the plumes, bringing low-density material closer to the Earth's surface.
Ghosh's team calculated the geoid low formed around 20 million years ago but there are no concrete conclusions whether the anomaly would disappear or shift away.
"That all depends on how these mass anomalies in the Earth move around," she explained.
Dissenting Opinions on Gravity Hole Study
Cardiff University professor Huw Davies said the research was "certainly interesting" and has described an interesting hypothesis that could be further studied in the future. However, he noticed
Meanwhile, University of Florida geology professor Dr. Alessandro Forte, who was not involved with the study, said while there is good reason to carry out computer simulations to determine the origin of the gravity hole as an improvement over earlier ones, there are still issues about its execution.
"The most outstanding problem with the modeling strategy adopted by the authors is that it completely fails to reproduce the powerful mantle dynamic plume that erupted 65 million years ago under the present-day location of Réunion Island," he said.
Forte explained the eruption of lava flows that covered half of the Indian subcontinent during that time, which also produced the Deccan Traps, one of the largest volcanic features on Earth, have long been attributed to a powerful mantle plume that went completely absent from the model simulation.
He also noticed the difference between the geoid, or surface shape, predicted by the computer simulation and the actual one were especially noticeable in the Pacific Ocean, Africa, and Eurasia.
In her team's defense, Ghosh responded that not every possible factor could be accounted for in the simulations because there is no recognizable pattern about how the Earth looked like in the past, all the more, confidence is lost in the models the farther back in time someone went.
