Why Is It Hot Inside The Earth?

The outside of the earth is a crust of rock which is about 10 to 30 miles thick. When we go down into this crust, we find that it begins to get hotter and hotter. For about every 40 meters we go down, the temperature grows one degree higher.

At two miles below the surface of the earth the temperature is high enough to boil water! If it were possible to dig down 30 miles, the temperature would be about 1,200 degrees Centigrade. This is hot enough to melt rocks. At the centre of the earth, scientists believe the temperature to be about 5,500 degrees Centigrade.

The crust of the earth has two layers. The upper layer, which makes the continents, is made up of granite. Under the layer of granite is a thick layer of very hard black rock called "basalt". This layer supports the continents and forms the basins that hold the oceans. At the centre of the earth, it is believed that there is a huge ball of molten iron, with a diameter of about 4,000 miles.

How did the centre of the earth get to be this way? According to most scientific theories, the earth and sun were once related in some way. Most scientists believe that the earth was once a hot, whirling mass of gas, liquid, or solid that began its regular trips around the sun. As years went by, it slowly cooled and the large mass grew smaller. As it whirled, it slowly took a ball-like shape. It was red-hot and held in its path by the attraction of the sun.
As the earth cooled, a hard crust formed on the surface. Nobody knows how long it took for the crust to form. But underneath that crust there remained the hot centre core of the earth, and it is still there today.