Structure of the earth

What is the Structure of the Earth?

The earth is a huge square with a radius about 6400 km. To find out the inner structure of the earth, we would have to go down right up to its centre. Obviously that is not possible. So, scientist have taken the help of earthquake to determine the structure of the earth.

 During earthquakes, vibrations are produced. Just as the vibrations of the string of a musical instrument produce sound waves, the earth's vibration produce seismic waves. The seismic Waves travel through different materials inside the earth at different speeds.They also get bent when they pass from one kind of material to another.

How many layers of the earth?

 By observing the path and speed of a seismic wave, scientists can find out the types and arrangement of the materials through which it passed. From such observation we now know that the Earth consists of three concentric layers
the crust,mental and the core.

The layers of the Earth

The crust 

The uppermost layer of the Earth is known as the core.The crust is very thin,with an average thickness of about 35 kilometre.If we could think of the earth as an egg, the current could be regarded as the shell.

 However, the crust is not uniformly thick at all places. It is thinner under the ocean and thicker under the continent.

The upper part of the continental crust, which is rich in silica and Aluminium, is called sial ( si is for silica and al is for aluminium ).

The lower part of the continental Crust and the whole of the ocean crust are composed mainly of denser material rich in silica and magnesium. They are together called Sima. (si is for silica and ma is for magnesium).

For example, mount Everest the highest mountain peak in the world, is 8848 metre above the sea level, while the world's deepest point located in the Mariana trench in the Pacific Ocean, is 11034 metre below sea level.

The Mantle 

Below The crust lies the mental. It extends upto the about 2900km.Its chief constituent are silicates of iron and magnesium.

Both the temperature and the density of the mantle increase with increasing depth towards the centre of the earth.

The Mantle has two parts 
the upper mantle and the lower Mantle. 

The upper mantle about 670 thick, while the lower mantle is nearly 2200 km thick.The top layer of the upper mantle is solid.Below this layer lies a soft layer.

Because of the high temperature in this layer, the rocks  here are in a soft state, a stage they reach just before melting. This layer begins at depth of about 50 kilometre and extent roughly up to a depth of 300 km.

The lithosphere, which comprises the crust and the hard uppermost part of the mantle, floats on this soft layer. Below this layer, the rocks of the upper mantle become harder with depth.

The lower mantle is a solid region starting at about 700 kilometre. Unlike the upper mantle, it is composed of rocks of uniform hardness.

The core 

 the innermost layer of the earth is called the core. It is about 3500 km thick.It is the densest layer.It is believed to be made up of heavy metals like Iron and Nickel,and is called the nife (ni is for Nickel and fe is for ferrum- Latin for iron).

 The temperature at the core are high enough to melt all metals. The study of seismic waves show that the outer part of the core is molten, while its innermost part is solid.