Friday, May 25, 2012

Inside the Earth

What is there inside the earth?

            Man has always bee 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 earth quake 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 s the core.

The internal structure of the earth

            The outer layer or the earth’s crust has two sub-layer-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-aluminum). Thus, the earth’s crust is mainly composed of silica. Its depth varies form 16 kilometers to 50 kilometers on land and about 5 kilometers 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 meters in depth, there is an increase of about 1 degree centigrade in temperature. At a depth of 3 kilometers, the temperature is around 100 degree centigrade boiling point of water and at 50 kilometers; the temperature is 1,200 degree centigrade- hot enough to melt rocks.

            The second layer, which is below the crust, is called the mantle. It is 2,880 kilometers thick. It is mainly composed of silicon, magnesium 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 cores. The outer core is liquid, and the inner core is solid. Its thickness is about 3482 kilometers. Its temperature is around 4800 degree centigrade. Its volume is 15% of that of the earth, while its weight is 32% of the earth’s weight. This solid core is surrounded form all sides by molten iron and nickel. Its temperature is around 3900 degree centigrade. The thickness of this molten mass is around 2.240 kilometers. The centre of the earth is some 6,336 kilometers form the earth’s surface.