Death of Ocean 180 Million Years Ago Left Hole in Indian Ocean

Earth’s gravitational field has an unusual anomaly known as a “gravity hole,” located in the Indian Ocean. This gravity hole is the deepest dent in the planet’s gravitational field, where sea levels are 348 feet lower than anywhere else on Earth due to an exceptionally weak gravitational pull in the area.

Although the gravity hole was first discovered in 1948, its origins remained a mystery until a 2023 study proposed an explanation. The study suggests that the gravity hole is the result of the collapse of an ancient ocean called Tethys, which existed between the supercontinents Laurasia and Gondwana. The study, published in Geophysical Research Letters, reveals that the death of Tethys contributed to the formation of the gravity anomaly in the Indian Ocean.

Spanning an area of 3.1 million square kilometers, the gravity hole is located 1,200 kilometers southwest of India. To understand its formation, researchers simulated the movement of Earth’s mantle and tectonic plates over the past 140 million years. Their models showed that Tethys sank beneath the Earth’s crust around 180 million years ago, as Gondwana broke apart. This caused pieces of the crust to slide under the Eurasian plate, with fragments sinking deep into the mantle.

The study also suggests that about 20 million years ago, these crustal fragments displaced high-density material from what is known as the “African blob,” which is trapped beneath Africa. This blob, made of crystallized magma, extends 100 times higher than Mount Everest. As plumes of low-density magma rose and replaced the existing magma, the mass of the region decreased, leading to the weakening of the area’s gravity.

However, the research is still preliminary and requires further verification using earthquake data to confirm the existence of the low-density plumes beneath the gravity hole. Similar blobs are believed to exist in Earth’s mantle, even in regions where they are not expected. Interestingly, Mars is also thought to have similar blobs under its surface, and understanding these phenomena on Earth could help scientists learn more about the interior of the red planet.