Interior of Earth, Explanation, Layers, Structure, Diagram

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

Interior of Earth is divided into 3 layers i.e Crust, Mantle and Core. Check more about Interior of Earth its Layers, Structure and Diagram for UPSC Exam.

Table of Contents

Interior of Earth

Earth has different layers based on what they are made of and their physical properties. The main layers are the core, mantle, and crust. In terms of mechanical properties, they include the lithosphere, asthenosphere, lower mantle, outer core, and inner core.

At the very center of the Earth is the inner core, which is solid iron and about 1221 kilometers wide. It is extremely hot, with temperatures as high as the surface of the sun (around 5200°C) but the immense pressure keeps it solid. The heat comes from the decay of radioactive elements, leftover heat from when the planet formed, and heat from the outer core solidifying. The inner core rotates in the same direction as the Earth’s surface, but slightly faster, completing an extra rotation every 1000 years or so.

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	Rocks from the mining area Volcanic Eruptions
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:

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

Crust

The Earth’s crust is its cold, fragile, and rocky outer most layer.
Two types of crust: continental crust and oceanic crust.
Thickness varies: the oceanic crust is about 5 km thick, continental crust is around 30 km thick.
Continental crust is made up of various metamorphic, igneous, and sedimentary rocks.
The crust accounts for about 0.5% of Earth’s mass and over 1% of its volume.
Oceanic crust forms from basalt lava flows when magma erupts under the seafloor. As it cools, it forms intrusive igneous rocks.
Primarily composed of silica (Si) and aluminum (Al), often called SIAL.
Average density of the crust’s components is 3 g/cm³.
The boundary between the hydrosphere and the crust is known as the Conrad Discontinuity.

Mantle

The mantle is the next layer beyond the Earth’s crust.
The boundary between the crust and mantle is called the Mohorovich Discontinuity (Moho Discontinuity).
The mantle is about 2900 km thick.
It makes up approximately 84% of Earth’s volume and 67% of its mass.
Known as SIMA because it is primarily composed of silicon and magnesium.
The density of the mantle ranges from 3.3 to 5.4 g/cm³, higher than the crust.
The Lithosphere includes the entire crust and the topmost solid part of the mantle.
The asthenosphere, located just below the lithosphere (between 80 and 200 km), is a viscous, weakly elastic, ductile zone.
The asthenosphere is the main source of magma and the layer over which tectonic plates move.
The Repetti Discontinuity is the boundary between the upper and lower mantles.
The mesosphere is the region of the mantle above the core and below the lithosphere and asthenosphere.

Core

The deepest layer surrounding Earth’s core.
Guttenberg’s Discontinuity separates the mantle from the core.
Also called NIFE due to its nickel (Ni) and iron (Fe) content.
Makes up nearly 15% of Earth’s volume and 32.5% of its mass.
Core density ranges from 9.5 to 14.5 g/cm³.
Composed of two sub-layers: the inner core and the outer core.
Inner core is solid; outer core is liquid (or semi-liquid).
Lehmann Discontinuity separates the upper core from the lower core.
The term “barysphere” can refer to the entire interior of the planet or just its core.

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/cm³in 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.

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.