A mysterious ‘gravity hole’ in the Indian Ocean has puzzled scientists for years. What is a ‘gravity hole’, you may ask? It’s not an easy concept to grasp, but we’ll try our best to explain it without getting too technical.
Basically, it’s a large region under the ocean where gravity is weaker than normal, which makes the seafloor sink lower. It’s not a tiny region, either.
It covers about three million square kilometres, which is a huge part of the planet to be unsure about.
So, what causes this ‘gravity hole’? Two brave scientists from India’s Institute of Science – Debanjan Pal and Attreyee Ghosh – have proposed a possible answer.
Their answer involves something that happened 1,000 kilometres – or 621 miles – below the Earth’s surface, where they found a cold and dense area that is the leftover of an ancient ocean that was dragged into a ‘slab graveyard’ under Africa about 30 million years ago, stirring up a lot of melted rock along the way.
Still with us? Good. Let’s continue.
The two scientists studied how tectonic plates have moved over the Earth’s surface over 140 million years, running simulations and then comparing them to the underwater depression that is this gravity hole.
They found that the simulations that matched the Indian Ocean geoid low as it looks today all had similar features, including streams of hot and low-density magma rising up under the low point.
The scientists think these streams of magma – and the mantle structure – create the gravity hole.
Still confused? Well, let’s let them explain it in their own words.
“In short, our results suggest that to match the [shape and amplitude of the] observed geoid low, plumes need to be buoyant enough to come up to mid-mantle depths,” said the duo.
The first plume such as this one appeared about 20 million years ago, just at the south of the Indian Ocean geoid low, about 10 million years after the Tethys Sea sank down into the Earth’s lower mantle.
The plumes moving around beneath the lithosphere heading slowly up towards the Indian peninsula saw the geoid low intensify.
It’s tough stuff to get into, but it is interesting once you attempt to get your head around it.
There’s a lot more research to be done to find out what the definitive truth is, as not all members of the scientific community are convinced by this argument.
