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Layers of the earth

Have you ever eaten the double-decker sandwich? You may see there are different layers of ingredients present in it. Some of the ingredients are soft and hard, some are hot and some are sticky. Similarly, our earth is also made of different spherical layers. Each layer has a unique speciality and significance. Without them, Earth would not have become what it is today. It gives us the necessary minerals and ores that are frequently employed in all fields. These layers provide all the necessary resources, including magnesium, nickel, iron, and petroleum. Let's learn about the various layers of the earth.

Table of content

  • Introduction
  • Classification of the earth’s layer compositionally
  • Classification of the earth’s layer mechanically
  • Practice problems
  • FAQs

Introduction

According to geologists, when the Earth cooled, the denser, heavier material sank to the centre and the lighter material rose to the surface. Because of this, the innermost layer is composed of nickel and iron, and the outermost layer is formed of the lightest materials, such as rocks and granite. Let's discuss the many layers of the earth.

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There are two ways to categorise the Earth’s layers: chemically (or compositionally) and mechanically.

Chemically (or compositionally), it can be separated into the crust, the mantle (which can be further divided into the upper and lower mantle), and the core (which likewise comprises an outer core and an inner core).

Mechanically, it can be broken down into the lithosphere, asthenosphere, mesospheric mantle, outer core, and inner core. The compositional separation is the more well-known of the two. Let's discuss it !

Classification of the earth’s layer compositionally

Based on composition, there are three divisions: crust, mantle, and core. Oceanic and continental crust, which makes up less than 1% of the Earth's total mass, typically contains more felsic rock. Approximately 68 percent of the mass of the Earth is in the heated mantle. The core's primary metal composition is iron. About 31% of the Earth is made up of the core. Lets discuss them one by one.

  • Crust : It is the solid outermost portion of the earth and is typically 8 to 40 kilometers thick. Its nature is brittle. The crust makes up about 5% of the earth's mass and almost 1% of its volume. Oceanic and continental regions have different crustal thicknesses. The oceanic crust is 5 km thinner. The thickness of continental crust about 30 kms. Silica (Si) and aluminum (Al) are the two main components of crust, which is why it is frequently referred to as SIAL. The crust's components have an average density of 3 g/cm3. The Conrad Discontinuity is the name given to the separation between the hydrosphere and the crust.
  • Mantle : The mantle is the area of the interior that is below the crust. The Mohorovich Discontinuity, or Moho discontinuity, is the separation between the crust and the mantle. The mantle has a thickness of around 2900 km. The mantle makes up around 84 percent of the earth's volume and 67 percent of its mass. The mantle is also known as SIMA since it primarily consists of silicon and magnesium. The layer's density, which ranges from 3.3 to 5.4 g/cm3, is higher than that of the crust. The Lithosphere is made up of the entire crust and the topmost solid portion of the mantle. Just below the lithosphere, in the upper mantle, is the asthenosphere, which is very viscous, mechanically weak, ductile, and deforming. Repetti Discontinuity is the name given to the transition between the upper and lower mantles. The region of the mantle just above the core and below the lithosphere and asthenosphere is referred to as the mesosphere.
  • Core : It is the deepest layer which is close to the earth center. Because of Guttenberg's discontinuity, the core and mantle are separated. It also goes by the name NIFE since it is mostly made of iron (Fe) and nickel (Ni). 32.5 percent of the earth's mass and roughly 15% of its volume are made up by the core. With a density of 9.5 to 14.5 g/cm3, the earth's core is the densest layer. The two sub-layers that make up the Core are the inner core and the outer core. The outer core is liquid, while the inner core is in a solid condition (or semi-liquid). The Lehmann Discontinuity is the separation of the upper core from the lower core.

Classification of the earth’s layer mechanically

Based on mechanical properties, the earth layer can be divided into the five sub-layers such as, Lithosphere, Asthenosphere, Mesosphere, Outer core and inner core. Let discuss them one by one,

  • Lithosphere : The entire crust plus the uppermost part of the mantle make up the lithosphere, which is the Earth's outermost layer. It may be extremely thin, only a few kilometers thick, beneath the oceanic crust or mid-ocean ridges, or extremely thick, 150 km or more thick, beneath the continental crust, particularly mountain belts. Around 70 km of thickness is normal. They are additionally separated into parts known as tectonic plates. These plates' movements are also responsible for earthquakes, volcanic eruptions, and the creation of oceanic trenches.
  • Asthenosphere : The flexible mantle layer on which the lithosphere flows is known as asthenosphere. It is 100 to 350 kilometers of depth. Despite being made of solid silicate components, it may flow for very extended periods of time due to the high temperature. At the lithosphere-asthenosphere boundary, geophysicists tell the two layers can be distinguished by their degree of ductility.
  • Mesosphere : The layer that lies above the outer core and beneath the asthenosphere is called the mesosphere. Essentially, it is the lower mantle. Typically it has a depth 350 to 2900 kilometers. The strong pressure in this area prevents the molecules of the silicate substance from moving freely despite the high temperature, making the material highly stiff.
  • Outer Core: The outer core extends from the lower mantle or mesosphere. The extreme temperature allows these metals, which are composed of iron and nickel, to maintain their liquid states. It is the only layer of the Earth that is truly liquid. Additionally, the magnetic field is created by its movement.
  • Inner Core: Iron and nickel are found in the inner core. It's a solid ball, unlike the outer core. The tremendous pressure from the higher layers is what gives the solidity. Since the liquid outer core at the border with the inner core cools and solidifies as a result of the gradual interior cooling, it is hypothesised that the inner core is slowly expanding even though it is as hot as the surface of the Sun.

Practice problems

Q1. What are the different layers of the earth and what are their compositions?
Answer.
There are three main layers of the earth which are,

  1. Crust: It is 5% of the earth's mass and almost 1% of its volume
  2. Mantle: It is 67% of its mass and around 84% of the earth's volume.
  3. Core: It is 32.5 % of the earth's mass and roughly 15% of its volume

Q2. What are the various discontinuities between the earth layers?
Answer.
The various discontinuities are listed below,

  1. Conrad discontinuity - It is the separation between the hydrosphere and crust.
  2. Mohorovicic discontinuity - Discontinuity between the lower crust and upper mantle.
  3. Repiti discontinuity - Discontinuity between the upper and lower mantle.
  4. Guttenberg discontinuity - Discontinuity between the lower mantle and outer core.
  5. Lehmann discontinuity - Discontinuity between the outer and inner core.

Q3. What are the different parts of the earth as per the mechanical classification and what are their depths?
Answer.
Mechanically earth layers can be classified as,

  1. Lithosphere: Upto 100 kilometres
  2. Asthenosphere : 100 to 350 kilometers
  3. Mesosphere: 350 to 2900 kilometres.
  4. Outer Core: 2900 to 5100 kilometres.
  5. Inner Core: 5100 to 6378 kilometres.

Q4. What are the two forms of the crust on the Earth?
Answer.
There are two types of crust. One is the continental crust which is less dense and thicker. The other is the oceanic crust which is dense and thin.

FAQs

Q1. What is the Earth's outer core's temperature?
Answer.  The outer core of the Earth has a temperature ranging from 4,000 to 9,400 degrees Fahrenheit.

Q2. What is the thickness of the Earth's widest portion and where is it located?
Answer. The largest portion of the Earth is its mantle. It measures over 2,900 kilometres thick.

Q3. Which layer of the Earth is in its centre and is the hottest?
Answer.  The hottest part of the Earth is located in its centre, called Inner Core.

Q4. Which metals are found in the Outer Core?
Answer. Metals like nickel and iron make the outer core.

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