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| 'Gravitational hole': How did the deepest part of the Earth's surface come into existence and why is the gravity low here? |
When we were taught about the earth in school, the teachers used to tell us that its shape is spherical and its shape changes at its poles. We are also told that its gravity is 9.8 meters per square second.
In reality, the shape of the earth is like a potato, it is by no means perfectly circular, but its upper surface is not uniform and has many irregularities.
Therefore, gravity is not the same in every region of the earth. Where the gravity is greater than the mean, it is positive and where it is less, it is negative. This is the discussion where the 'Gravitational Hole' is discussed.
"A gravitational hole is a region where gravity is the most different than any region on Earth," says Gabriela Fernández, professor of geology at the University of Oviedo.
However, they also say that this 'hole' is not an area where things sink, nor does it travel at high speeds, nor is it visible.
Gravity scales on ships measured this change a decade ago, and modern satellites have since measured it more accurately.
However, there is no concrete explanation in the past as to why this is so. However, a study has now shown very clearly why this change in gravity might have occurred.
A 'gravitational hole' is the deepest place on Earth's surface. It is located in the Indian Ocean and south of Peninsular India. It is in the shape of a round circle where the surface is 105 meters below the mean sea level. It is spread over three lakh square kilometers.
Experts call this region the Indian Ocean Low Geode (IOLG) and there are various hypotheses about its existence.
However, we have a place to start researching.
If you remember, in school we also read that gravity is proportional to mass. Therefore, if the substance or mass is less, the gravity will also be less.
With this basic point in mind, we can say that the region of the gravitational hole has less mass or matter. This is the explanation from which geophysicists have started their research. However, scientists have not yet agreed on why there is less mass or matter.
What are the different assumptions?
"So far, all the models show that the lack of mass in this part of the Indian Ocean is because the oceanic plates collided with each other," says Fernandez.
The sea floor in this region was called the Tethys Ocean in ancient times and it was located between the continents of Gondwana and Laurasia during the Mesozoic Era. This is about 6.6 million years to 25 million years before the Indian Ocean appeared here.
When the Indian plate broke off from the supercontinent of Gondwana and collided with the Eurasian plate, the Tethys plate sank into the Earth's mantle, creating an ocean.
Seismic velocities, on the other hand, are a piece of information known to geologists and explain the fluctuations in Earth's temperature and surface. "All the information we have underground is related to seismology," Fernandez says.
Geoscientists Dibanjan Paul and Atrey Ghosh from the Indian Institute of Science are the authors of a recent study on the same. "Previously published research only focused on what it was, not why it happened," he says.
A new model
Paul has spent years trying to explain this beyond the creation of the plates in the Mesozoic Era.
Paul's team tested 19 different scenarios of tectonic plate movement and examined changes in the Earth's mantle over the past 140 million years.
For this, they tested various parameters, including the viscosity or density of the Earth's mantle, its temperature, and the collision of the plates and the resulting ruptures. He inspected it through satellites.
The results for six of these appeared to match the upper surface data of the Indian Ocean. If the Tethys oceanic plates were important in the models used earlier, Paul and Ghosh's research found that it was "necessary to cause it but not the main cause."
When the Indian plate broke off from the Gondwana supercontinent and collided with the Eurasian plate, the Tethys plate, which had an ocean on it, sank into the Earth's mantle. This information was also available in our previous research. However, now another part of the earth also joined it and that was East Africa.
During these millions of years the Tethys Plate, which Fernández says, "moved into the lower mantle, traveling all the way to Africa where it collided with hot magma, particularly beneath East Africa."
The collision of this cold plate with the hot plate created vibrations and created a material that moved toward the Indian Ocean where the gravitational hole is located.
The material that moved is called 'mantle plumes', which is actually hot magma that is less dense and rises faster than the rest of the material.
Fernández says that ``mantle feathers are found in other places where there is less density and less gravity, so it can be said that this low mass. It was because of Fatah that there was less gravity. However, in the Indian Ocean, this was not so clear, nor was it known where this low-density material came from.
"Paul and Gosh have shown that mantle feathers are here and that they came from somewhere else," she says.
In his opinion, the new model "uses geological history, specific data, and mantle convection models."
Fernandez says that this further refines the theory of plate tectonics.