While it is easy to imagine the Earth as a perfect sphere that has uniform gravity all over, that is far from the case. But that is not the case; our planet is flat at the poles and it bulges at the equator. Also, it doesn’t have uniform gravity everywhere. For example, there is a massive “gravity hole” in the Indian Ocean and now, researchers have uncovered why that is the case. The strength of the gravitational pull at any part of the world is dependent on the mass of the Earth’s crust, mantle and core beneath that particular region. Interestingly, a massive region in the Indian Ocean, about 1,200 kilometres southwest of the southernmost tip of India, has such a low pull of gravity that the sea level of the Indian ocean over the “hole” is around 106 metres below the global average, according to Scientific American. This pronounced dip in the ocean is called Indian Ocean geoid low (IOGL) and was discovered in 1948 during a survey by Dutch geophysicist Felix Andries Vening Meinesz. Since then, it has been confirmed by other ship-based experiments and with measurements from satellites. But scientists haven’t really been able to conclusively say why it happens. Until now that is. In a research article published in the journal Geophysical Research Letters, Debanjan Pal and Attreyee Ghosh, researchers from the Indian Institute of Science (IISc) in Bengaluru, document what they believe caused the gravitational anomaly. After looking at computer-simulated models of the past 140 million years, they found the remains of an ancient ocean about 965 kilometres below the Earth’s crust, just under Africa, according to BBC. In all the simulations, the researchers found molten rock plumes below Africa, which could potentially have been caused by tectonic plates plunging into the mantle. They believe that these plumes could be the reason behind IOGL. But the researchers told New Scientist that there is no clear seismographic evidence that the plumes in the simulations are actually present beneath the Indian Ocean. They believe that there are still other factors behind the dip that need to be uncovered before a conclusion can be made.
