por What is the asthenosphere?
The asthenosphere It 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 alternating structure, since it is in the solid state but under both heat and duress, it adopts a moldable (or plastic) form, allowing isostasy to develop, a gravitational process that balances the crust and the contiguous mantle of the earth.
However, this process is carried out when the seismic waves accelerate their speed due to the increase in the depth of the upper channel. That is to say, when the frequencies of the asthenosphere present a fluctuation 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 presents changes at the moment of its fluctuations.
The oscillating function of the asthenosphere is highly relevant, since its convection process intervenes in the atmosphere through the movements of the continental plates and the oceans. It also influences the planet’s climatic exposure, creates new territories, and fuels the growth of plant life.
Training
What element is given the name of 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, a zone 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 idea of dividing the Earth into two channels—a rigid one a hundred meters thick and the other elastic and indefinitely deep—appeared for the first time in 1914, thanks to the American Joseph Barrell.
For this scientist, the Earth’s surface is made up of several different layers (in this case, two), but they 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 naming it, seismology did not exist. Therefore, Barrell’s proposal was not supported, since 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 about 200 kilometers.
According to this seismologist, this effect occurs when the rigidity of the materials found in the dark area of what is now called the asthenosphere decreases. In 1926 the statement of the existence of a moldable layer was considered irrefutable.
It was in the 60s when an idea about the asthenosphere was revived. In 1962 Don Anderson stated that the crust does indeed have a heterogeneous inner layer. The novelty of the work presented by this geophysicist is that he showed evidence, which consisted of underground nuclear tests from the 50s.
In these essays —which follow the line proposed by Anderson in relation to the location, time and energy of the explosions— it is established that the low speed zone is found both in the continents and in the oceans. This is intended 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 decrease more quickly in the latter. That 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 established a controversy, because for many scientists the concept of the asthenosphere had been eliminated or was even non-existent.
union of guesses
Joseph Barrell’s Upper Sphere Hypothesis and Don Anderson’s Low Velocity Area Hypothesis were studied as two different theories, but ended up merging into one due to the slight divergence between them.
According to Barrell, the upper sphere is nothing more than a layer where rocks transmute from rigid to plastic and flow through geological time. Instead, for Anderson, this multiple layer extends progressively and reduces seismic velocities, whether in the oceanic or continental masses.
This theoretical deformation caused seismologists to study the rocky zone as a universal level of low seismic velocity with certain steps of abrupt increases. In addition, they returned to him the name that had been given to him: asthenosphere.
Characteristics of the asthenosphere
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.
The highest viscosity rate is located on this rocky layer, although in its mechanical work it is the most fragile area compared to the rest of the areas and the Earth’s surface. This is because it is made up of semi-cast and compact components.
It also has the function of expanding, stimulating and originating the restoration of the ocean floor through an extrusion process. That is, the components of the layer are extracted and flow by the ridges of the oceanic levels.
It also renews the continental masses, since the P (compressive) and S (shear) waves of the Earth travel through a zone that, like the asthenosphere, is of low speed.
The heat that arises from this layer flows into the interior of 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 kilometers of depth it is solid.
This area is made up of mineral fragments derived from supernova explosions, which expel the layers of stars through shock waves. These layers are identified as 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 magma liquid freezes. In addition, it contains aluminum, sodium and potassium; elements that contribute to the creation of the basalt rock, whose pigmentation darkens the layer. For this reason it is known as dark space.
Differences with lithosphere
The lithosphere occupies the Earth’s crust and upper mantle. It is the outermost and coldest layer of the planet. Its depth is about 100 kilometers, but it can reach 250 in the oldest continents.
Unlike the asthenosphere, the lithosphere is relatively rigid, that is, it has a rocky shell that does not flow fluidly.
However, its cover is not continuous, but divided, since it consists of a dozen plates that move across the surfaces at low speeds. While the rhythm of the asthenosphere varies, that of the lithosphere appears to be a slight shift.
Density
The asthenosphere is a layer with greater density, which is why its molten minerals flow perennially. Instead, the minerals of the lithosphere are under great pressure and temperature, becoming more rigorous and discontinuous instantly by accelerating the mechanism of their seismic waves.
Contrary to the asthenosphere, geologists verified the existence of two lithospheres: one oceanic and one continental.
Why is its existence disputed?
The existence of the asthenosphere has been problematized since it began to be studied as a universal rocky zone of low seismic velocity. In this sense, the layer that lies below the continental lithosphere and not the oceanic one is being questioned.
For specialists in geology, this continental layer is non-existent for the simple fact that the 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 to the path of time, also has a great influence.
References
Anderson, DL The plastic layer of the earth’s mantle. Recovered from usuarios.lycos.es.
Anguita, F. Bye-bye, asthenosphere. Recovered from ucm.es.
Barrell, J. The evolution of the earth and its inhabitants. Retrieved from biodiversitylectures.org.
Sidney, PC Structure of the earth. Retrieved from documents.unican.es.