What is there inside the Earth?

          Man has always been curious to know about the internal structure of the Earth. He tried digging and other direct methods and, finally, found out an indirect method to know the interior of the Earth – through the study of earthquake vibrations of Seismic waves. Studies reveal that our Earth has three main layers – the outer surface on which we live is called the ‘Earth’s crust’, below it is the ‘mantle’ and then comes the ‘core’.

          The outer layer or the Earth’s crust, has two sub-layers – the first layer is the lighter one and is called Sima (for silica – magnesium) while the second sub – layer is heavier than the first and is called ‘Sial’ (for silica – aluminium). Thus, the Earth’s crust is mainly composed of silica. Its depth varies from 16 km to 50 km on land and about 5 km under the oceans. The volume of this crust is only 1% of the Earth’s volume, while its weight is around 4% of the Earth’s total weight. As we go down the Earth’s crust, the temperature increases. At every 35 metres in depth, there is an increase of about 1° C. At a depth of 3 km, the temperature is around 100° C (boiling point of water) and at 50 km, the temperature is 1,200° C – hot enough to melt rocks.

          The next layer below the crust is called ‘mantle’. It is 2,880 km thick. It is mainly composed of silicon magnesia and iron. The rocks in the mantle are denser than sial and sima. Its total volume is 84% of the Earth’s volume. Its weight is around 67% of the Earth’s weight.

          The central portion of the Earth is called ‘core’ which is made up of high-density solid materials, in Free State or in combined form in rocks. Its thickness is about 3482 km. Its temperature is around 4800° C. Its volume is 15% of that of the Earth, while its weight is 32% of the Earth’s weight. This solid core is surrounded from all sides by molten iron and nickel. Its temperature is around 3900°C. The thickness of this molten mass is around 2,240 km. The centre of the Earth is some 6,336 km from the Earth’s surface.