Scientists reveal origins of the giant "gravity hole" in the Indian Ocean

The gravity hole in the Indian Ocean, a place where gravity weakens to an extreme low, has been a puzzle for scientists. Now, computer models may have found that it may be the result of an ancient sea.

Earth, often depicted as a perfect sphere, is actually characterised by an irregular shape resembling a potato. This uneven surface is attributed to the non-uniform distribution of gravity across the planet, resulting in anomalies known as geoids. The gravity hole in the Indian Ocean is one such intriguing feature.

According to a report in Science Alert, this region, known as the Indian Ocean geoid low (IOGL), spans approximately 2 million square kilometres. The study, published in the journal Geophysical Research Letters, reveals that the IOGL is formed from remnants of an ancient sea called Tethys. It once separated the mega-continents of Gondwana and Laurasia.

Geologists have long been fascinated by the origins of the IOGL. A recent study by two Indian geologists, Debanjan Pal and Attreyee Ghosh from the Indian Institute of Science (IISc), utilised more than a dozen computer models to arrive at their findings. They retraced the formation of the massive geoid by modelling how tectonic plates skimmed over Earth's hot, gooey mantle during the past 140 million years.

Professor Ghosh, an Assistant Professor at the Centre for Earth Science, stated, "All these [past] studies looked at the present-day anomaly and were not concerned with how this geoid low came into existence." According to their hypothesis, the Indian tectonic plate was just starting to break away from the supercontinent, Gondwana, to begin its northward march. As the Indian plate advanced, the seabed of an ancient ocean called the Tethys Sea sank into Earth's mantle, and the Indian Ocean opened up behind it.

"They think the answer lies more than 1,000 kilometres (621 miles) beneath Earth's crust, where the cold, dense remnants of an ancient ocean plunged into a 'slab graveyard' beneath Africa some 30 million years ago, stirring up hot molten rock," said the report in Science Alert.

The researchers discovered that the presence of lighter materials, known as "low-density anomalies," in the upper to mid-mantle (the layer between the Earth's core and crust) below the IOGL, contributes to the gravity low observed in this area. Their findings were based on extensive computer modelling and simulations. According to Professor Pal, the "gravity hole" likely assumed its current shape around 20 million years ago and is expected to persist for millions of years into the future.

In simpler terms, the IOGL represents a significant deviation from the normal gravitational pull experienced across Earth. This anomaly is attributed to the presence of lighter materials beneath the Indian Ocean, dating back millions of years to the existence of an ancient ocean.

The study sheds light on a longstanding geological puzzle, providing a deeper understanding of the complex forces shaping the planet.