Earth was formed about 4.6 billion years age. Roughly ball like in shape, 71% of the earth is covered by water and rest 29% by land. The earth is made up of several layers which can be divided into three main layers: crust, mantle and the central core.
The upper most crust varies in thickness from about 8 km under the oceans to about 40 km under the continents. This layer is mainly composed of silica and constitutes one percent of the Earth’s total volume and four percent of total weight.
The crust is further divided into two layers: the upper Sima and heavier, lower Sial. There temperature increases by 1 degree C for every 35 meters as one goes down into the Earth. At a depth of three km the temperature reaches 100 degree C where water starts boiling and at 50 km the temperature reaches 1200 degree C.
Mantle is the next layer below the crust. It is a layer of solid rock about 2900 km thick and largely contains iron and magnesium. It constitutes 84% of the Earth’s total volume and 67% of the total weight.
The inner most cores is made up of two layers. At the centre is solid core of an iron nickel alloy under pressure. It is about 2560 km thick and a temperature of 8000 degree C.
It constitutes 15% of total volume of the Earth and 32% of its weight. This layer is surrounded by 2250 km thick liquid outer core is composed mainly of nickel and iron and also silicon and sulphur.
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