For years, researchers have tried to pinpoint how an area deep in the Indian Ocean with lower gravitational pull came to be. A team in India may have figured it out.
The area in question is called the Indian Ocean Geoid Low and sea level above it is nearly 348 feet (106 meters) lower than the global average. Earth’s gravitational pull is comparatively lower in this region and it is the Earth’s lowest geoid, said researchers from the Indian Institute of Science.
“If you’re in a ship passing through the area, you won’t perceive any change,” Attreyee Ghosh, one of the team’s researchers, told USA TODAY. “The change is taking place very gradually, over a very, very, very large distance.”
The team wanted to find out how the geoid low formed, so they used supercomputers to run simulations ranging from the Cretaceous period millions of years ago to the present. The simulations included the shift of the Earth’s tectonic plates.
The team ran 19 simulations and in 6 of them, the Indian Ocean Geoid Low formed, said Ghosh, who researched the case with Ph.D. candidate Debanjan Pal.
Their findings were published this year in the peer-reviewed journal Geophysical Research Letters. They discovered that once sinking slabs from a prehistoric ocean moved many years ago and reached the Earth’s mantle, plumes formed, making way for the Indian Ocean Geoid Low.
Ghosh said it is important for these cold slabs to sink and reach the bottom of the mantle and simulate the plumes.
Without the slabs, there would be no plumes and without the plumes, the Indian Ocean Geoid Low wouldn’t exist.
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The Earth’s interior includes a mantle, or the path between the core and the outer crust, Ghosh said. The mantle condensed and went through a process called convection.
Ghosh compared it to boiling water being heated from the bottom. The hot water is lighter and rises while the cold water sinks down.
“Something similar is happening in the mantle,” she said. “The core is very hot and this hot material is light, so it’s rising up and at the surface, it’s becoming cold. It’s sinking inside the mantle.”
And while many people think the Earth is a perfectly-shaped sphere, it isn’t so simple, said Ghosh.
The Earth is actually more like a “lumpy potato,” she said. As the Earth rotates, it bulges at the equator and flattens at its poles.
The Earth’s interior is also made of different materials that impact gravity, creating lumps called geoids, like the one in the Indian Ocean.
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Prehistoric ocean partially responsible for Indian Ocean Geoid Low
The research team said the formation of the Indian Ocean Geoid Low is due in part to a prehistoric ocean that is long gone.
The Earth looked very different millions of years ago, Ghosh said. India, for example, was in the southern hemisphere, “very close to Antarctica.” Time passed and India split from Antarctica, moving northward and colliding with Asia.
“That’s where we have the Himalayas now,” she said.
Calling it a “lost ocean,” Ghosh said a prehistoric ocean called the Tethys Ocean previously sat between India and Asia and disappeared as India split from the southern hemisphere.
The cold, dense oceanic plate sank inside the Earth’s mantle, which is extremely hot, she said. Hot materials then began to rise, creating plumes and ultimately, the Indian Ocean Geoid Low.
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Limitations of the study and what this means
One of the study’s limitations is the lack of perfect replication. The team’s knowledge of the Earth millions of years ago can’t be perfectly simulated, Ghosh said.
“We have an idea about what the tectonic plates were, what kind of density structure there was, but these are uncertainties and the earlier we go back in time, the uncertainties increase,” she said.
While the team’s findings don’t directly impact people’s lives, Ghosh wants people to know how important it is to understand what’s happening inside the planet we live on.
The research team set out to find out how this geoid came to be because there’s so much we don’t know about the Earth’s interior.
“We can use telescopes to look at what’s happening on the surface of Mars or Venus but when it comes to the Earth’s interior, we do not have any kind of direct way of looking,” Ghosh said.
“We know a lot more about the surfaces of distant stars than we know what’s going on inside the earth.”
