ASTHENOSPHERE: FORMATION, CHARACTERISTICS AND COMPOSITION - GEOGRAFÍA - 2025

The asthenosphere is one of the inner layers of the earth's crust, which is located between the lithosphere and the mesosphere. Its function is to allow the displacement of the continental masses. The word asthenosphere derives from the Greek, and its meaning is "weak".

This layer is usually identified by its alternate structure, since it is in a solid state but under so much heat and pressure that it adapts to a moldable (or plastic) shape, generating isostasy, a gravitational process that balances the crust and the contiguous mantle of the earth.

The asthenosphere is located between the lithosphere and the mesosphere. Source: USGS

However, this process is carried out when seismic waves accelerate their speed due to the increase in the depth of the upper channel. That is, when the frequencies of the asthenosphere show a swing between the descents and the elevations, resulting in the alteration of the properties of the rocks.

In this sense, this solid and semi-fluid layer -which can descend up to three hundred kilometers- is determined by the low speed of its frequencies, but it shows changes at the time of its fluctuations; therein lies its value.

The oscillating function of the asthenosphere has great relevance, since its convection process intervenes in the atmosphere through the movements of the continental plates and the oceans. It also influences the climate exposure of the planet, creates new territories and promotes the growth of plant life.

Training

What element is called the asthenosphere? At the low-speed level of seismology where seismic echoes vary or, rather, where mechanical waves make their way late.

History

The origin of the formation of the asthenosphere, an area of ​​the mantle located 30 to 130 kilometers deep below the lithosphere, is unclear. Even today, the theory related to the generation of the asthenosphere remains incongruous for some authors.

The division of the earth into two channels - one rigid one hundred meters thick and the other one of indefinite depth and elastic - appeared for the first time in 1914; This notion was determined by the American Joseph Barrell.

For this scientist, the surface of the Earth is made up of several layers (in this case, two) that differ but act as a whole. The names he proposed for such units were: asthenosphere, upper sphere and lithosphere, and rocky sphere.

It should be noted that at the time of their appointment there was no seismology, a branch that is responsible for the study of seismic waves. For that reason, Barrell's proposal was not supported as it lacked numerical data.

Next hypothesis

Some time later, the German Beno Gutenberg formulated another hypothesis based on the fact that in certain areas the speed of seismic waves decreased by around 5%, corresponding to a depth of 200 kilometers.

According to the German seismologist, this effect occurs when the rigidity of the materials found in the dark area of ​​what is now called the asthenosphere diminishes. In 1926, the statement about the existence of a moldable layer was once again considered irrefutable.

It was in the 1960s that an idea about the asthenosphere was revived. In 1962, Don Anderson stated that the crust certainly has an inner layer that is heterogeneous. The novelty of the work presented by this geophysicist is that it shows evidence, which consists of the underground nuclear tests of the 1950s.

In these essays - which follow the line suggested by Anderson in relation to the location, time and energy of the explosions - it is established that the low speed zone is found both on the continents and in the oceans. This is to explain that this level is essential when determining the frequencies of the planet.

Likewise, it expresses that the layer of solid and fluid features is a global phenomenon, but its trajectory in the continental or oceanic masses is diverse since the waves diminish more rapidly in the latter. This happens because the continental zone is not limited to the crust, but occupies thousands of kilometers of the depth of the mantle.

However, this argument forged a controversy because for many scientists the concept of asthenosphere had become widespread or even non-existent.

Conjecture union

The hypothesis about a superior sphere proposed by Joseph Barrell and the approach about an area of ​​low seismic speed by Don Anderson were studied as two different theories, but they ended up merging into one due to the meager divergence between them.

According to Barrell, the upper sphere is nothing more than a layer where the rocks transmute from rigid to plastic and flow through geological time. On the other hand, for Anderson this multiple layer progressively extends and reduces seismic speeds, either in the oceanic or continental masses.

This theoretical deformation caused seismologists to study the rocky zone as a universal level of low seismic speed with certain steps of abrupt increases. In addition, they returned the name that had been given to it previously: asthenosphere.

characteristics

Heat storage

Despite being such a questioned structure, the asthenosphere is characterized by storing heat from the mesosphere and sending it to the lithosphere through a convection system that, in the end, enables the movement of tectonic plates.

High viscosity

The highest viscosity rate is located on this rocky layer, although in its mechanical work it is the most fragile zone compared to the rest of the areas and the surface of the Earth. This is because it is made up of semi-cast and compact components.

Participation in the ocean floor

It also has the function of expanding, stimulating and causing the restoration of the ocean floor through an extrusion process. That is, the components of the layer are extracted and flow through the ridges of the oceanic levels.

Action on the continental masses

As for the continental masses, it also renews them, since the Earth's P (compression) and S (shear) waves travel through an area that, like the asthenosphere, is of low speed.

The heat that arises from this layer flows into the crust, causing the rocks to acquire a moldable property and transform, at the same time it can form earthquakes and the eruption of magma from volcanoes.

Composition

The asthenosphere is one of the layers that structures the Earth and one of the areas where some of its physical properties are found. It is characterized by being plastic on the upper side, and throughout the 200-kilometer depth it is solid.

This area is made up of mineral fragments that derive from supernova explosions, which expel the layers of the stars through shock waves. These layers are identified by being masses of natural crystal or grains of iron, oxygen, silicon and magnesium.

Therefore, the asthenosphere is a rocky level composed mainly of magnesium and iron silicates. The union of both natural components produces sedimentary and metamorphic rocks, ferromagnetic minerals, as well as magmatic and radioactive material.

That is, it is a layer of igneous rock that is generated when the liquid in the magma freezes. In addition, it contains aluminum, sodium and potassium; these elements contribute to the creation of basalt rock, whose pigmentation darkens the layer. For this reason it is known as dark space.

Differences with lithosphere

The lithosphere occupies the crust and upper mantle of the Earth; it is the outermost and coldest layer on the planet. Its depth is about 100 kilometers, but it can reach 250 on the oldest continents.

Unlike the asthenosphere, the lithosphere is relatively rigid; that is, it has a rocky shell that does not flow smoothly.

However, its cover is not continuous but fractional, since it consists of a dozen plates that move across surfaces at low speeds. While the rhythm of the asthenosphere varies, that of the lithosphere appears to be a slight displacement.

Density

The asthenosphere is a layer with higher density, which is why its molten minerals flow in a perennial way. Instead, the minerals of the lithosphere are under great pressure and temperature, becoming more rigorous and discontinuous at the moment of accelerating the mechanism of their seismic waves.

Contrary to the asthenosphere, geologists verified the existence of two lithospheres: one oceanic and the other continental.

Why is its existence disputed?

The existence of the asthenosphere has become problematic since it began to be studied as a universal rocky zone with low seismic speed. In this sense, the layer that is under the continental lithosphere and not the oceanic one is being questioned.

For geologists, this continental layer is non-existent due to the simple fact that soils develop differently in the many territories of the planet.

In addition, the rapid growth that occurs in the field of seismic tomography, where the movements of mechanical waves do not correspond with the trajectory of time, also has a great influence.

References

1. Anderson, DL (1962). The plastic layer of the earth´s mantle. Retrieved on April 5, 2019 from Scientific American: users.lycos.es
2. Anguita, F. (2002). Bye-bye, asthenosphere. Retrieved on April 6, 2019 from the Complutense University of Madrid: ucm.es
3. Barrell, J. (2003). The evolution of the earth and its inhabitants. Retrieved on April 6, 2019 from the National Academy Press: biodiversitylectures.org
4. Chirinos, G. (2014). Internal structure of the Earth. Retrieved on April 6, 2019 from Research Library: Bibliotecadeinvestigaciones.wordpress.com
5. Sidney, PC (2008). Structure of the earth. Retrieved on April 5, 2019 from the University of Cantabria: documents.unican.es