July 4th 2023.
Have you ever wondered why gravity is not the same everywhere on Earth? The shape of the Earth is not a perfect sphere, which leads to unevenness in the gravitational force at different points. This phenomenon is called ‘geoid anomalies’ and it occurs because of the uneven mass distribution within the Earth.
The weakest dent in the Earth’s gravitational field can be found in the Indian Ocean near the Indian peninsula. This area has been termed as the ‘Indian Ocean geoid low’ where the gravitational pull is the least compared to other parts of the planet. The ocean surface here plunges to 106 metres.
Since ancient times, scientists have been trying to explain the reason behind this low in the Earth’s gravity. Recently, researchers from the Centre for Earth Sciences at the Indian Institute of Science in India have presented a model that explains this phenomenon. According to their findings, the dent may be caused by ancient tectonic plates sinking underneath the Indian Ocean, resulting in a plume of hot mantle, which is less dense than the sunken crust, rising above it.
The model revealed that the oceanic slabs reached the lower mantle about 30 million years ago, and within the next 10 million years, the neighbouring upwelling plume under the Indian Ocean was established.
Mountain ranges, such as the Himalayas, have a high concentration of mass, and therefore have a strong gravity field. Since the oceans cover 71% of the planet’s surface, these deformities affect the shape of the oceans too.
Professor Attreyee Ghosh, one of the authors of the study, said “The existence of the Indian Ocean geoid low is one of the most outstanding problems in Earth Sciences. It is the lowest geoid/gravity anomaly on Earth and so far no consensus existed regarding its source.”
So, the Indian Ocean geoid low is an example of how the Earth’s plates are constantly shifting, and how the interior of the Earth is still a mystery. While we have sent spacecrafts to explore the outer reaches of the galaxy, we are yet to send probes that go beyond the base of the Earth’s crust.
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