How do we know so much about the Earth's core if we have barely reached a depth of 12 kilometers?

How do we know so much about the Earth's core if we have barely reached a depth of 12 kilometers?

From where you are, no matter where you are when you read this text, to the center of the planet, there are 6,370 km. That is roughly the average radius of the Earth, an area of ​​enormous mysteries.

To unveil them, we have even drilled ambitious holes such as the 12,226 meter Kola Super Deep Well. That is, below the limit of this hole there are 6,358 kilometers of planet left until reaching its center. So how do we know the architecture of the Earth if we have barely scratched its surface?

In the beginning, all that man had to enter the planet were the natural caverns that he was finding and exploring while imagining myths of the underworld, from the domain of Hades and the River Styx to the monumental novel 'Journey to the Center of the Earth' by Jules Verne.

To know the depths of the earth, the first approach, perhaps the most obvious, is to drill as much as possible. Mining operations were the first to advance in what we now know to be the earth's crust, until in the 20th century projects such as the Kola project were launched, started in 1970 and abandoned due to lack of funds in 1995. It reached to cover a third of the terrestrial crust of the Baltic, bringing to light rocks up to 2,700 million years old, of the 4,500 million that the planet has.

study of volcanic rocks

The second way of knowing the interior of the planet is the study of the rocks expelled by the volcanoes and the geological faults; that is, places where blocks of rock from the most superficial part of the Earth have broken, allowing us to see the composition of the different strata that form it. The farther from the surface a layer is, the older it is, so we can read the history of the planet in them. Likewise, volcanoes expel from the depths of the mantle ancient rocks, xenoliths, and ancient crystals, xenocrystals such as diamonds, which are wrapped in magma and provide us with information about those places that we have not yet reached. Diamonds are formed in specific conditions at 150 kilometers or more, so what goes with them (or what is embedded in them) comes from those depths.

Another way to learn about our planet is to study the seismic waves that spread out from the site of an earthquake like those that move in the water when we throw a stone into a still pond. Earthquake waves are altered by the different densities of the rock through which they travel, and by studying their variations using seismographs in different locations, scientists can infer what the rocks they pass through are like.

Thus, the seismologist Inge Lehman was able to determine that the center of our planet was not liquid metal, but rather a solid core that reflected the seismic waves that collided with it. The enormous density and pressure to which the iron core -mainly- of our home is subjected prevent it from melting, as would be expected. This is how we discovered the furthest point on the Earth's surface, the core, which begins at 2,900 kilometers and divides into the solid inner core of about 2,400 kilometers in diameter and an outer core made up mainly of liquid iron, which is the outer layer. responsible for the earth's magnetic field and has a thickness of about 2,300 kilometers.

Magnetic field measurement

Measuring the Earth's magnetic field is another way of looking inside it, as it informs us of the greater or lesser presence of magnetic rocks. Since our magnetic field changes over time, the electrical conductivity of different areas of the surface can be measured to determine their composition. This has allowed us to discover large amounts of water in the Earth's mantle.

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Much of what we know has been obtained in laboratories where the hypotheses derived from all these types of observations are tested by creating temperatures and pressures similar to those inside the planet to see how different materials behave. The behavior of matter under these extreme conditions is usually very different from what we know in our environment, and thus we have been able to know how it is that the inner core remains in a solid state (or in a state similar to the solid that only exists at those pressures). ) and that its temperature is about 6,100 °C, in fact hotter than the photosphere or visible surface of the sun, which is at about 5,500 °C.

From space we can also study our planet. Gravity is not completely uniform throughout it, as has been verified thanks to satellites such as those of NASA's Grace mission, which for 15 years, since 2002, studied the Earth's gravitational anomalies. Gravity depends on mass, and therefore these fluctuations show us areas of the planet where there are materials of higher density, and have even allowed us to detect long-term changes in the earth's crust due to earthquakes.

From space we also get meteorites with the elements with which the solar system and our planet were formed. By analyzing some elements, mainly radioactive, from meteorites and from the Earth's crust, it is possible to reconstruct part of the planet's history and how, about 4.5 billion years ago, large amounts of dust and rocks coalesced into a fiery ball. collapsing under its own weight, where most of the heavy elements such as iron and nickel sank to the core and the lighter ones such as silicon, oxygen and carbon rose to the surface to create the crust, remaining in middle of the Earth's mantle.

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The mantle is a layer of rock about 2,900 kilometers thick, whose upper part, the asthenosphere, is semi-molten and on which the crust floats, so to speak, divided into large areas called 'tectonic plates', which are constantly changing. movement, while the inner mantle is less fluid due to the pressures to which it is subjected.

And it is in that cortex where we develop. Especially in the continental crust, the thickest, which is between 35 and 70 kilometers thick, while the oceanic crust can be barely 8 kilometers.

This view is greatly simplified, of course. The continuous movement and transition zones between these layers is still a matter of study and debate among geologists. But knowing our home is a fundamental task since, according to all indications, this is where our future lies, bright or dark.

A changing core

The inner core of our planet is not static, but rather grows by about 1 millimeter each year, and in the 1990s it was discovered that its eastern side is growing faster than its western side.

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