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# What is there inside the Earth?

Man has always been curious to know as to what lies inside the Earth. He tried digging and various other methods and finally, found an indirect method to know — through the study of earthquake vibrations or 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 innermost part known as 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 kilometres to 50 kilometres on land and about 5 kilometres 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 deeper into the Earth’s crust, the temperature increases. For every 35 metres in depth, there is an increase of about 1°C in temperature. At a depth of 3 kilometres, the temperature is around 100°C (boiling point of water) and at 50 kilometres, the temperature is 1,200°C — hot enough to melt rocks. The second layer, which is below the crust, is called the ‘mantle’. It is 2,880 kilometres thick. It is mainly composed of silicon, magnesum 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 innermost portion of the Earth is called ‘core’ which is made of high-density solid materials. The core has two parts —outer core and inner core. The outer core is liquid, while the inner core is solid. Its thickness is about 3482 kilometres. 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 kilometres. The centre of the Earth is some 6,336 kilometres from the Earth’s surface

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