Physical geography of India and World
Economic and Human Geography of India and World

Interior of the Earth

#Interior of the Earth, #Direct Sources, #Indirect Sources, Interior of the Earth

Interior of the Earth
Interior of the Earth
Why is Earth’s inner core solid explained!
Different Layers of the Earth
What Is Earthquake | How it occurs, causes | Seismic Waves | P and S Waves
Types of Volcanoes | Characteristics, differentiation and Classification

The interior of the earth can be understood only by indirect evidences as neither anyone has nor anyone can reach the interior of the earth. The radius of earth is 6370 km.

Interior of the Earth

Direct Sources

There are two direct sources one is to reach the crust and second is by volcanic eruption.

For example – gold mines in South Africa are as deep as 3-4 km. Going beyond this depth is not possible as it is very hot at this depth.

Scientists have taken up number of projects to penetrate deeper depth. Such as

  • Deep Ocean drilling project
  • Integrated ocean drilling project

The deepest drill at Kola in Arctic Ocean has so far reached a depth of 12 km.

During the process of Volcanic eruption when magma is thrown out of the surface of the earth, it becomes available for laboratory analysis.

Indirect Sources

We know through the mining activity that the temperature and pressure increase with increasing distance from the surface towards the interior in deeper depths.

Indirect Sources


Interior of the Earth
  • The shaking of the earth is called an earthquake.
  • It is caused due to the release of energy, which generates waves that travel in all direction.
  • The point where the energy released is called the focus of an earthquake. It is called the hypocentre.
  • The point on the surface near the focus is called the epicentre.
Earthquake Waves

All natural earthquakes take place in the lithosphere. Lithosphere refers to the portion of depth up to 200 km from the surface of the earth. An instrument called ‘Seismograph‘ records the waves reaching the surface.

Earthquake Waves
Shadow Zone

Earthquake waves get recorded in Seismographs located at far off locations. However, there exist some specific areas where the waves are not reported. Such a zone is called a shadow zone.

P-wave shadow zone
S-wave shadow zone
Types of Earthquake
Effects of Earthquake
Effects of Earthquake

Structure of the Earth

Structure of the Earth
Structure of the Earth
The Crust
  • It is the outermost solid part of the earth.
  • The thickness of the crust varies under the oceanic and continental areas.

Continental Crust vs Oceanic Crust

  • Oceanic crust is thinner as compared to the continental crust.
  • The mean thickness of the oceanic crust is 5 km whereas that of the continental is around 30 km.
  • The continental crust is thicker in the areas of major mountain systems.
  • It is as much as 70 km thick in the Himalayan region.It is made up of heavier rocks having a density of 3 g/cm3.
  • This type of rock found in the oceanic crust is basalt.
  • The mean density of material in oceanic crust is 2.7 g/cm3.
The Mantle
  • The portion of the interior beyond the crust is called the mantle.
  • The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
  • The upper portion of the mantle is called asthenosphere.
  • The word astheno means weak. It is considered to be extending upto 400 km.
  • It is the main source of magma that finds its way to the surface during volcanic eruptions.
  • It has a density higher than the crust’s (3.4 g/cm3).
  • The crust and the uppermost part of the mantle are called lithosphere.
  • Its thickness ranges from 10-200 km. The lower mantle extends beyond the asthenosphere. It is in solid state.
The Core
  • The earthquake wave velocities helped in understanding the existence of the core of the earth.
  • The core-mantle boundary is located at the depth of 2,900 km.
  • The outer core is in liquid state while the inner core is in solid state.
  • The density of material at the mantle core boundary is around 5 g/cm3.
  • At the centre of the earth at 6,300 km, the density value is around 13g/cm3. The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nife layer.


A volcano is a place where gases, ashes and/or molten rock material – lava – escape to the ground.

The mantle contains a weaker zone called asthenosphere. It is from this that the molten rock materials find their way to the surface.

The material in the upper mantle portion is called magma. Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.

On the basis of nature of eruption and the form developed at the surface. Major types of volcanoes are as follows:

Shield Volcanoes

Barring the basalt flows, the shield volcanoes are the largest of all the volcanoes on the earth. The Hawaiian volcanoes are the most famous examples. These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted.

Composite Volcano

These volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt. These volcanoes often result in explosive eruptions. Along with lava, large quantities of pyroclastic material and ashes find their way to the ground.

Volcanic Landforms

The lava that is released during volcanic eruptions on cooling develops into igneous rocks.

The cooling may take place either on reaching the surface or also while the lava is still in the crustal portion. The lava that cools within the crustal portions assumes different forms.

Depending on the location of the cooling of the lava, igneous rocks are classified as

  • volcanic rocks (cooling at the surface)
  • plutonic rocks (cooling in the crust)

The origin and Evolution of the Earth

Structure of the Earth