The shape of the earth according to the different gravitational values it gives. The darkest area is the “gravity hole”.
When the Earth is studied in primary school, it is usually explained to us that its shape is that of a sphere flattened at the poles. We later learn that its gravity is 9.8 m/s2.
The fact is that the Earth is like a potato: it is not a homogeneous ball, but a geode with many irregularities. This also assumes that its density is different in every region of the globe, and therefore, gravity is not the same everywhere.
Thus, on Earth there are parts in which the standard value of gravity used in its study differs. This difference is called Anomaly, and it can be positive, when the value of gravity (g) is higher than the standard, or negative, when it is lower.
This is where the “gravity hole” comes in.
Gabriela Fernández Viejo, a geologist from the University of Oviedo, told BBC Mundo that this area has “a huge, massive, most significant gravitational anomaly on Earth”.
However, the expert cautions, this “hole” is not an area where things sink, things don’t fall out faster, not even a visible hole.
Gravity meters on ships measured this anomaly decades ago, and more advanced satellites have since improved the calculations.
but There was no clear explanation as to why this phenomenon occurred.
So far, a recent study shows precisely how this anomaly can occur.
What is this
This “gravity hole” is the lowest point on Earth’s geoid. Located in the Indian Oceansouth of the Hindustan Peninsula.
he A circular depression 105 meters below sea level.
And you have one It extends over 3 million square kilometres.
The name that experts know is the Indian Ocean Low Geospatium (IOGL) and there are many hypotheses about how this space, which records the lowest gravity on the planet, was created.
But there is a basic starting point.
If we remember what we were taught in elementary school, we certainly remember that gravity is proportional to mass. Thus, less mass means there is less gravity.
From this point of view, that In the “gravity hole” region there is less mass, It is from him that all the explanations of geophysicists began. What they don’t agree on is why this smaller amount of mass is worth it.
image source, Getty Images
See the earth from space.
Many hypotheses, none completed
“The models that have existed so far have explained the mass loss in the Indian Ocean based on the fact that there is a series of Planks Or oceanic plates that subducted upon impact,” says Fernandez.
the Planks The crusts in this area are ancient and come from ancient Tethys, an ocean that was between the continents of Gondwana and Laurasia in the Mesozoic Era, a period between 250 million years and 66 million years ago, before the emergence of the Indian Ocean.
When the Indian plate separated from the supercontinent Gondwana to collide with the Eurasian plate, the Tethys plate, which formed an ocean between them, sank into the mantle.
In this model of Earth’s gravity, the “gravity hole” in the Indian Ocean is seen in dark blue.
On the other hand, seismic velocities are part of the information that geologists know and can be explained by the different densities and temperatures of the planet’s layers. Fernandez makes it clear “The only data we have from the Earth’s interior are those that refer to seismology.”
And precisely in this previous models failed.
“They said that this gravitational anomaly is only due to Planks It was not explained by other things, such as seismic velocities in the area,” says Fernandez.
Geologists Dipanjan Pal and Atrey Ghosh of the Indian Institute of Science and authors of the latest research on this phenomenon, They argue that “previous studies looked at the current anomaly and did not care how it might arise.”
new model
Pal spent years trying to explain the origin of this anomaly after the creation of the Mesozoic plates.
With advances in computing, he was able to create a model that, in Fernandez’s opinion, “Most compelling, it explains data about seismic velocities, why it happened over time, what movements in tectonic plates occurred and when the phenomenon of following the same movement could end.
Pal’s team simulated 19 different scenarios for tectonic plate movement and changes in the Earth’s mantle over the past 140 million years.
To do this, they used various parameters, such as the viscosity or density of the mantle, the temperature, the resistivity of the plate plates or the deformation time.
In each simulation they played with different values of these parameters and compared the result with the data that actually existed, that is, with the real geoid of the Earth observed by satellites.
In six of the simulations, the shape and extent of the Indian Ocean low geodes closely matched the actual data.
This means that after playing with 19 different possible scenarios, the results of 6 of them coincided with what we observe in nature today.
An illustration of what the Earth’s interior will be like with its layers, with different and contrasting composition, viscosity and temperatures.
Why is it happening
If in previous models the oceanic plates of Tethys were key, in Pal and Ghosh’s study their contribution is “essential for the generation of anomalies, but secondary”.
When the Indian plate separated from the supercontinent Gondwana to collide with the Eurasian plate, the Tethys plate that formed an ocean between them sank into the mantle. So here this was what we got in previous studies.
But now another part of the planet is in play: East Africa.
Over tens of millions of years, the cold Tethys Plate slid into the lower mantle and traveled toward Africa, where it interacted with an area of hot magma, specifically under East Africa, Fernandez says.
From this interaction between a cooler plate and a warmer plate, a turbulence occurs, a kind of plume that in turn flows back into the Indian Ocean, where the gravitational anomaly is currently located.
This moving material is known as “mantle plumes” and is hot, less dense magma and precisely because of these properties it rises above the rest of the material.
Fernandez asserts that “in other low-density, low-gravity regions, the presence of mantle feathers could be seen, and thus it was possible to say that the cause of this low gravity was less dense material. But in the Indian Ocean it was not so clear, and it was not known where the material came from.” least dense.
“What Pal and Ghosh do is show that there are feathers in the mantle because they came from somewhere else,” he says.
In the expert’s opinion, the new model developed by the Indian Center “adapts geological history, objective data, and mantle convection models.”
It revises the theory of plate tectonics, Fernandez says.
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