What are the importance of Earth's Layers (Crust, Mantle and Core)

 The seismic waves are the waves of energy that moves through the earth’s layer as a result of forming earthquakes, volcanic eruptions, magma movement, and landslide, etc. seismic waves are primarily of two types:

1) Body waves: A body wave is a seismic wave that moves through the interior of the earth. Body waves arrive before the surface wave emitted by an earthquake, these waves are of higher frequency than the surface wave.

2) Surface wave: The seismic wave that travels through the crust or along the earth's surface, such seismic waves are called surface waves. they have low frequency and are the most destructive wave.

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          The study of seismic waves, which travel through below the earth’s surface gives a basic idea about the structure of the earth’s interior and the physical properties of its various layers. The seismic waves travel with different velocities in different layers depending on their nature. So they not only indicate the position of each layer but also give clues to its composition.

On the basis of earthquake investigation, the earth's interior can be divided into three major layers.

1) Crust: The outer superficial layer of earth is called “crust”. It extends down to 30-40 km beneath the continent and to about 10 km beneath the ocean basins. At the bottom of the crust, the velocity of earthquake waves increases abruptly as they enter into the denser layer called “mantel”. The mantel-crust boundary is known as “Mohorovicic discontinuity”. 

     In the continental region, the crust layer can be divided into two layers. The upper layer is less dense and granitic in character which is known as “sial”. While the lower layer is basaltic in nature, known as “sima”. The word sial represents the rocks rich in silica and aluminum and the term sima represents the rocks rich in silica and magnesia.

Under the ocean, only a sima layer is found and the sial layer is absent.

 

       2)  Mantle: The mantel is located beneath the earth’s crust and has a thickness of about 2900 km. The mantel part is further divided into two layers. Upper mantle and lower mantle.

           The boundary between the upper mantle and lower mantle is about 700 km in depth.

           a)    Upper Mantel: As its name suggests that it is the topmost layer of the earth’s Mantle part. The average mineral composition of this layer is similar to the ultrabasic rocks like “Peridotite”. This layer provides lava for oceanic eruption. The upper Mantel layer contains an important layer, known as the asthenosphere. It is located at a depth of 50-100 km. In the asthenosphere, the velocity of secondary waves decreases, which indicates this zone, is consisting of melted rock. The magma chamber is also found in this layer.

          b)   Lower Mantle: It is the lowermost layer of the mantle part as its name suggested. The lower mantle layer consists of calcium-silicate perovskite, bridgmanite, ferropericlase, and some other minerals.

 

3) Core: the boundary between the mantel and core is at the depth of about 2900 km. The core part can be divided into two parts: 

The outer core was discovered when it was found that the primary wave bent inward thereby producing a “shadow zone” at the surface. Since the secondary wave does not pass through the outer core, so it is concluded that it may be in the liquid state. The thickness of the outer core is about 2,200 kilometers approximately. 

The inner core extends from 5150 km to the earth center at 6371 km. It transmits the primary waves at a high velocity, which indicates that this inner core consists of a solid surface. Both the solid and the liquid portion of the core believes that consist of iron and nickel similar to iron metered has a density of about 1.2*10^3 kg m^-3