This page gives some information about the earth internal structure

Do you know how old the earth is?
That sounds crazy...yeah? But scientists have calculated from their study that the earth is about 4.6 billion years old.... amazing isn't it.
There are different method used to find out the date of a rock. The most popular method is by using half life time of an element found in the rock.
One of the method used to date a rock is carbon dating method, but this is useful only for rocks that are formed after organisms appeared on the earth.
This is mainly because carbon is found only in the organic matter.

What is radius of the earth?
Well that sounds another crazy question, but we have the answer.
The approximate calculated radius of the earth is around 6370 kms. However, radius at the equator is around 22 km more than at the poles.

The other interesting thing to know would be the structure of deep interior of the present earth.
It is a difficult question to answer since nobody can really see the deep interior of the earth.
How ever with big efforts of several scientists, a model of internal structure of the earth is made after studying lava that is erupted to the surface.
This was further supplemented by studying the records of earthquake data. This model can not be proved but theoretically this is
the best model presented till now and will be in use unless new discoveries show it to be wrong.

METAMORPHIC ROCKS
When an existing rock is subjected to temperature and pressure, a metamorphic rock is created. Due to heat atoms are transferred from one crystal to another and larger crystal are formed within the same rock. Some times larger particles are forced to change their shape due to pressure and thus a new rock is formed.

Mantle

The mantle lies below the earth crust and surrounds the central part, the core. The calculated thickness of mantle is around 3480 km. Part of the mantle is partially melted because of the high temperature and pressure at depth. This part is mainly made of rocks called peridotite.

CORE :
This is central part of the earth and can be distinguished into two parts, the central most part which is solid and mainly composed of heavy metallic material and the the outer core surrounding the central core which is liquid in nature.

The calculated thickness of the core is around 2900 km. It is mainly composed of Iron (Fe) with some Nickel (Ni).

Internal structural of the earth on the basis of physical properties
On the basis of physical properties earth can also be divided into different layers.

Lithosphere:
Outer layer made of mainly solid rocks. It is thick below continent and thin under oceans. However, average thickness of this layer is around 100 km.

Asthenospher:
This is the layer below Lithosphere and is mainly composed of solid rocks, which are partially melted. As depth increases temperature and pressure also increases, this results in partial melting of rocks. Thus such rocks are soft and flow easily.
The average thickness of this layer is around 250 km and goes up to depth of 350 km from the surface which includes the 100 km thick outer layer the Lithosphere.

Mesosphere:
This layer is also made of solid but soft rocks that are capable to flow easily. The average thickness of this layer is about 2500 km.

Outer core:
This layer is present below the mesosphere. It is composed of liquid rock material. An average thickness of this layer is about 2250 km.
Chemically this liquid layer is rich in iron and nickel.

Inner core:
This is the inner most part of the earth and made of solid earth material. It is mainly composed of heavy metals iron and nickel.

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