INTERNAL STRUCTURE OF THE EARTH: LAYERS AND THEIR CHARACTERISTICS - ENVIRONMENT - 2024

The internal structure of the Earth or geosphere, is the layer that includes from the rocks on the surface to the deepest areas of the planet. It is the thickest layer and the one that houses most of the solid materials (rocks and minerals) on Earth.

As the material that formed the Earth was being deposited, the collisions of the pieces generated intense heat and the planet went through a state of partial fusion that allowed the materials that form it to go through a process of decanting by gravity.

The heavier substances, such as nickel and iron, moved towards the deepest part or core, while the lighter substances, such as oxygen, calcium and potassium, formed the layer that surrounds the core or mantle.

As the Earth's surface cooled, rocky materials solidified and thus the early crust was formed.

An important effect of this process is that it allowed large amounts of gases to escape from the interior of the Earth gradually forming the primitive atmosphere.

The interior of the Earth has always been a mystery, something inaccessible because it is not possible to drill to its center.

To overcome this difficulty, scientists use the echoes originated by seismic waves from earthquakes. They observe how these waves are duplicated, reflected, delayed or accelerated by the various layers of the Earth.

Thanks to this, today, we have a very good idea about its composition and structure.

Layers of the Earth's Internal Structure

Since the studies about the interior of the Earth began, numerous models have been proposed to describe its internal structure (Educativo, 2017).

Each of these models is based on the idea of ​​a concentric structure, composed of three main layers.

Each of these layers is differentiated by its characteristics and its properties. The layers that make up the inner part of the earth are: the crust or outer layer, the mantle or intermediate layer and the core or inner layer.

1 - The crust

It is the most superficial layer of the Earth and the thinnest, constituting only 1% of its mass, it is in contact with the atmosphere and the hydrosphere.

99% of what we know about the planet, we know based on the earth's crust. Organic processes take place in it that give rise to life (Pino, 2017).

The crust, mainly in the continental areas, is the most heterogeneous part of the Earth, and it undergoes continuous changes due to the action of opposing forces, endogenous or builders of relief, and exogenous ones that destroy it.

These forces occur because our planet is made up of many different geological processes.

Endogenous forces come from inside the Earth, such as seismic movements and volcanic eruptions that, as they occur, build the land relief.

Exogenous forces are those that come from outside such as wind, water and changes in temperature. These factors erode or wear down the relief.

The thickness of the crust is varied; the thickest part is on the continents, under the great mountain ranges, where it can reach 60 kilometers. At the bottom of the ocean it barely exceeds 10 kilometers.

In the crust is a bedrock, made mainly of solid silicate rocks such as granite and basalt. Two types of crust are distinguished: continental crust and oceanic crust.

Continental crust

The continental crust forms the continents, its average thickness is 35 kilometers, but it can be more than 70 kilometers.

The greatest known thickness of the continental crust is 75 kilometers and is found under the Himalayas.

The continental crust is much older than the oceanic crust. The materials that compose it can date back 4,000 years and are rocks such as shale, granite and basalt, and, to a lesser extent, limestone and clay.

Ocean crust

The oceanic crust constitutes the bottoms of the oceans. Its age does not reach 200 years. It has an average thickness of 7 kilometers and is made up of denser rocks, essentially basalt and gabbro.

Not all the waters of the oceans are part of this crust, there is a surface area that corresponds to the continental crust.

In the oceanic crust it is possible to identify four different zones: the abyssal plains, the abyssal trenches, the oceanic ridges and the guyots.

The boundary between the crust and the mantle, at an average depth of 35 kilometers, is the Mohorovicic discontinuity, known as mold, named after its discoverer, the geophysicist Andrija Mohorovicic.

This is recognized as the layer that separates the less dense materials of the crust from those that are rocky.

2 - Cloak

It is under the crust and is the largest layer, occupying 84% of the volume of the Earth and 65% of its mass. It is about 2,900 km thick (Planet Earth, 2017).

The mantle is composed of magnesium, iron silicates, sulfides, and silicon oxides. At about 650 to 670 kilometers deep, a special acceleration of seismic waves is caused, which has made it possible to define a boundary between the upper and lower mantles.

Its main function is that of thermal insulation. The movements of the upper mantle move the tectonic plates of the planet; the magma thrown by the mantle at the place where the tectonic plates separate, forms a new crust.

Between both layers there is a particular acceleration of seismic waves. This is due to a change from a plastic mantle or layer to a rigid one.

In this way and to respond to these changes, geologists refer to two well differentiated layers of the earth's mantle: upper mantle and lower mantle.

Upper mantle

It is between 10 and 660 kilometers thick. It begins at the Mohorovicic (mold) discontinuity. It has high temperatures so the materials tend to expand.

In the outer layer of the upper mantle. It is part of the lithosphere and its name comes from the Greek lithos, which means stone.

It comprises the earth's crust and the upper and colder part of the mantle, distinguished as a lithospheric mantle. According to studies carried out, the lithosphere is not a continuous covering, but is divided into plates that move slowly over the surface of the Earth, at a few centimeters per year.

Following the lithosphere is a layer called the asthenosphere, which is made up of partially molten rocks called magma.

The asthenosphere is also in motion. The limit between lithosphere and asthenosphere is located at the point where temperatures reach 1,280 ° C.

Lower mantle

It is also called the mesosphere. It is found between 660 kilometers to 2,900 kilometers below the Earth's surface. Its state is solid and reaches a temperature of 3,000 ° C.

The viscosity of the upper layer is clearly different from the lower layer. The upper mantle behaves like a solid and moves very slowly. Hence the slow movement of tectonic plates is explained.

The transition zone between the mantle and the Earth's core is known as the Gutenberg discontinuity, named after its discoverer, Beno Gutenberg, a German seismologist who discovered it in 1914. The Gutenberg discontinuity is located about 2,900 kilometers deep (National Geographic, 2015).

It is characterized because secondary seismic waves cannot pass through it and because primary seismic waves decrease sharply in speed, from 13 to 8 km / s. Below this the Earth's magnetic field originates.

3

It is the deepest part of the Earth, has a radius of 3,500 kilometers and represents 60% of its total mass. The pressure inside is much higher than the pressure on the surface and the temperature is extremely high, it can exceed 6,700 ° C.

The nucleus should not be indifferent to us, as it affects life on the planet, since it is considered responsible for most of the electromagnetic phenomena that characterize the Earth (Bolívar, Vesga, Jaimes, & Suarez, 2011).

It is made up of metals, mainly iron and nickel. The materials that make up the core are molten due to high temperatures. The nucleus is divided into two zones: outer nucleus and inner nucleus.

External nucleus

It has a temperature between 4,000 ° C and 6,000 ° C. It ranges from a depth of 2,550 kilometers to 4,750 kilometers. It is an area where iron is in a liquid state.

This material is a good conductor of electricity and circulates at high speed on the outside. Because of this, electric currents are produced that originate the Earth's magnetic field.

Inner core

It is the center of the Earth, about 1,250 kilometers thick, and is the second smallest layer.

It is a solid metallic sphere made of iron and nickel, it is in a solid state although its temperature ranges from 5,000 ° C to 6,000 ° C.

On the earth's surface, iron melts at 1,500 ° C; however, in the inner core the pressures are so high that it remains in a solid state. Although it is one of the smallest layers, the inner core is the hottest layer.

References

1. Bolívar, LC, Vesga, J., Jaimes, K., & Suarez, C. (March 2011). Geology -UP. Obtained from Internal structure of the earth: geologia-up.blogspot.com.co
2. Educational, P. (2017). Educational portal. Obtained from Internal Structure of the Earth: portaleducativo.net
3. National Geographic. (July 7, 2015). Retrieved from Caryl-Sue: nationalgeographic.org
4. Pino, F. (2017). Explore. Obtained from Internal structure of the earth: vix.com.