Three Layers of Earth – Crust, Mantle and Core

Layers of Earth

Layers of Earth : Our Planet, the Earth is made up of different layers. Each layer of the Earth has unique properties. In 1692, Edmond Halley put forth the idea of a hollow Earth consisting of a shell about 500 miles (800 km) thick, two inner concentric shells and an innermost core. He suggested that atmospheres separated these shells, and that each shell had its own magnetic poles, with each sphere rotating at a different speed.

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Layers of the Earth

The Earth’s Layers

The three major layers of Earth are

1) Crust

2) Mantle

3) Core 

The Crust

  • The crust is the outer layer of the earth.
  • It is a thin layer between 0-60 km thick.
  • The crust is the solid rock layer upon which we live.
  • The Earth’s Crust is like the skin of an apple.
  • It is very thin in comparison to the other layers.
  • The crust is only about 3-5 miles (8 kilometers) thick under the oceans (oceanic crust) and about 25 miles (32 kilometers) thick under the continents (continental crust).
  • The temperatures of the crust vary from air temperature on top to about 1600 degrees Fahrenheit (870 degrees Celsius) in the deepest parts of the crust.
  • The crust of the Earth is broken into many pieces called plates.
  • The plates “float” on the soft, plastic mantle which is located below the crust.
  • These plates usually move along smoothly but sometimes they stick and build up pressure.
  • The pressure builds and the rock bends until it snaps. When this occurs an Earthquake is the result.
  • The seven continents and ocean plates basically float across the mantle which is composed of much hotter and denser material.
  • The crust is composed of two basic rock types granite and basalt.

What is SIAL & SIMA?

  • SIAL is upper layer of the Crust. It is made up of rocks abundant in silicate and aluminium based minerals.
  • SIMA is lower layer of the Crust. It is made up of rocks abundant in magnesium silicate minerals.
  • SIAL makes up a majority of continental crust. SIMA makes up a majority of oceanic crust.


  • The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere.


  • The layer below the rigid lithosphere is a zone of asphalt-like consistency called the Asthenosphere. It is the part of the mantle that flows and moves the plates of the Earth.

The Mantle

  • The mantle is the largest layer of the Earth, 1800 miles thick.
  • The mantle is composed of very hot, dense rock.
  • This layer of rock even flows like asphalt under a heavy weight. This flow is due to great temperature differences from the bottom to the top of the mantle.
  • The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km.
  • The mantle is made up of semi-molten rock called magma.
  • In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt.
  • The movement of the mantle is the reason that the plates of the Earth move.
  • The temperature of the mantle varies from 1600 degrees Fahrenheit at the top to about 4000 degrees Fahrenheit near the bottom.

The Core

Core is further divided into two layers. ie Outer Core and Inner Core.

Outer Core

  • The core of the Earth is like a ball of very hot metals. (4000 degrees F. to 9000 degrees F.)
  • The outer core is the layer surrounding the inner core.
  • The outer core is so hot that the metals in it are all in the liquid state and also made up of iron and nickel.
  • It is still extremely hot, with temperatures similar to the inner core.
  • The outer core is located about 1800 miles beneath the crust and is about 1400 miles thick.
  • The outer core is composed of the melted metals nickel and iron.

 Inner Core

  • The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place as a solid.
  • The inner core begins about 4000 miles beneath the crust and is about 800 miles thick.
  • The temperatures may reach 9000 ° F and the pressures are 45,000,000 pounds per square inch.
  • This is 3,000,000 times the air pressure on you at sea level.
  • The inner core is in the centre and is the hottest part of the Earth.
  • It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth.