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Interior of Earth, Sources of Information, Layers, Structure, Diagram

Interior of Earth

The Interior of the Earth refers to everything beneath the surface, excluding the atmosphere and hydrosphere. It’s a vast and hot realm, mostly hidden from direct observation. Scientists use indirect methods, like studying the travel times of seismic waves from earthquakes, to understand its structure. Because of the Earth’s immense size and the dynamic nature of its internal composition, direct observations of the Interior of the Earth are not possible. The distance between the human race and the earth’s centre (6,375 km) is practically unbridgeable.

Sources of Information about the Earth’s Interior

There are mainly two types of sources that give information about the interior of the Earth i.e. Direct sources and indirect sources.

Sources Details
Direct Sources
Indirect Sources
  • By examining the rate at which temperature and pressure change from the surface to the interior.
  • Meteors, because they are made of the same materials as the Earth.
  • Gravity is greater near the poles and less so near the equator. Gravity anomaly, defined as the change in gravity value as a function of material mass, provides information about the materials in the earth’s interior.
  • Seismic Waves: The shadow zones of body waves (primary and secondary waves) provide information about the state of materials inside the building.
  • Magnetic fields: The Earth is made up of layers with varying chemical compositions and physical properties. The Earth’s crust is permanently magnetised, and the Earth’s core generates its own magnetic field, which sustains the majority of the field we measure at the surface.

Diagram of Interior of Earth

Here’s a diagram of the Earth’s interior layers:

Diagram of Interior of Earth

Layers of Interior of Earth Layers

The three fundamental parts of the earth’s structure are the core, the mantle, and the crust. Only 15% of the Earth’s volume is made up of the core, and 84% is made up of the mantle. The crust represents the final 1% of the total.

  • The Crust
  • Mantle
  • Core

The Crust

The Crust of the Earth is the name given to its cold, fragile, and rock-based outer layer. There are two types of crust, each with unique physical and chemical characteristics: (i) continental crust; and (ii) oceanic crust. Basalt lava flows are produced when magma under the seafloor erupts, forming the oceanic crust. As it descends further, intrusive igneous rocks form. Numerous varieties of metamorphic, igneous, and sedimentary rocks make up the continental crust.

The crust makes up about 0.5% of the earth’s mass and over 1% of its volume. Oceanic and continental regions have various crustal thicknesses. The oceanic crust is 5 km thinner than the continental crust (about 30 km). Silica (Si) and Aluminium (Al) are the two main components of the crust, which is why it is Commonly referred to as SIAL. The crust’s components have an average density of 3g/cm3. The Conrad Discontinuity is the name given to the boundary between the hydrosphere and crust.

Mantle

The mantle is the area of the interior that is beyond the crust. The Mohorovich Discontinuity, often known as the Moho Discontinuity, is the separation between the crust and mantle. The mantle has a thickness of around 2900 km. The mantle is around 2900 kilometres thick. Approximately 84% of the earth’s volume and 67% of its mass are made up of the mantle. Because it is primarily composed of silicon and magnesium, the mantle is also known as SIMA.

The density of the layer, which ranges from 3.3 to 5.4g/cm3, is greater than that of the crust. The entire crust and the topmost solid portion of the mantle comprise the Lithosphere. An extremely viscous, weakly elastic, ductile, deforming zone of the upper mantle, the asthenosphere (between 80 and 200 km), is located just beneath the lithosphere.

The asthenosphere is the primary source of magma and the layer that the continental and lithospheric plates travel across. Repetti Discontinuity refers to the boundary between the upper and lower mantles. The mesosphere refers to the region of the mantle that lies immediately above the core and above the lithosphere and asthenosphere.

Core

It is the layer that surrounds the earth’s core that is the deepest. Guttenberg’s Discontinuity divides the mantle from the core. It is also called NIFE since it contains nickel (Ni) and iron (Fe). Nearly 15% of the earth’s volume and 32.5 per cent of its mass are made up of the core. The density of the earth’s core fluctuates around  9.5 and 14.5 g/cm3.

The inner core and the outer core are the sub-layers that make up the Core of the earth  The inner core is solid, but the outside core is liquid (or semi-liquid). A Lehmann The division of the upper core from the lower core is referred to as discontinuity. The entire interior of the planet or merely its core can both be referred to as the “barysphere.

Temperature, Pressure and Density of the Interior of Earth

Temperature

  • In mines and deep wells, the temperature rises with increasing depth. These findings, along with molten lava erupting from the earth’s interior, support the theory that the temperature rises towards the earth’s core.
  • The various observations show that the rate of temperature increase is not uniform from the surface to the centre of the Earth. Initially, the rate of temperature increase is 1°C for every 32 metres of depth increase.
  • The temperature rises at a rate of 120 degrees Celsius per kilometre in the upper 100 kilometres and 200 degrees Celsius per kilometre in the next 300 kilometres.
  • However, as one descends deeper, this rate drops to just 100 C per km. As a result, it is assumed that the rate of temperature increase beneath the surface decreases towards the centre (do not confuse rate of temperature increase with temperature increase).
  • The temperature is constantly rising from the earth’s surface to the centre. The temperature at the centre is estimated to be between 30000C and 50000C, but it could be much higher due to chemical reactions occurring under high-pressure conditions. Because of the heavy pressure of the overlying materials, the materials at the centre of the earth are solid even at such high temperatures.

Pressure

  • Pressure is increasing from the surface to the centre of the earth, just like temperature. This is due to the enormous weight of the overlying materials, such as rocks.
  • It is estimated that the pressure in the deeper portions is nearly 3 to 4 million times greater than the pressure in the atmosphere at sea level.
  • The materials beneath will melt towards the centre of the earth at high temperatures, but due to high pressure, these molten materials will acquire solid properties and are likely in a plastic state.

Density

  • The density of the earth’s layers increases towards the centre due to increased pressure and the presence of heavier materials such as nickel and iron.
  • The average density of the layers rises from the crust to the core, reaching nearly 14.5g/cm3 in the centre.

Interior of Earth UPSC

Only a few kilometres of the earth’s interior have we been able to directly witness through mining and drilling operations. Direct observations in the interior of the earth are mostly restricted by the quick rise in temperature below the surface of the planet. But even so, scientists have a good concept of what the interior of the earth looks like thanks to some direct and indirect sources.

This topic is of immense importance when it comes to UPSC Preparation. A candidate must be well-versed in Physical Geography. Notes for UPSC in addition to reading the UPSC Book and the NCERT Books for UPSC to cover this topic.

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Interior of Earth FAQs

What are the elements of Earth's interior?

Iron, oxygen, silicon, and magnesium, are elements that may combine to form the crystalline Minerals known as silicates, make up more than 90% of the Earth's mass.

Why is the Earth's interior hot?

Radioactive element decay, residual heat from planetary formation, and heat produced as the liquid outer core solidifies close to its boundary with the inner core the main cause of heat in the Core.

What per cent of the Earth is the inner core?

Nearly 15% of the earth's volume and 32.5 percent of its mass are made up of the core.

Which is the cold layer of the earth?

The crust is the cold layer of the earth, the more we go deep in the earth the hotter it is.

Which is the hottest layer of Earth?

The core is the hottest layer of Earth.

Which mineral does crust contain?

Silica (Si) and Aluminium (Al) are the two main components of the crust, which is why it is Commonly referred to as SIAL.

Which mineral does the core contain?

The core is also called NIFE since it contains nickel (Ni) and iron (Fe).

What is the density of the mantle?

The density of the layer, which ranges from 3.3 to 5.4g/cm3, is greater than that of the crust.

Which mineral does the mantle contain?

Because it is primarily composed of silicon and magnesium, the mantle is also known as SIMA.

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