If you travel from one place to another in your country, you might see physical features such as hills, mountains, valleys and lakes. In order to understand fully the features that we find on the earth surface, it is important to know what is inside the earth. What we know of the interior of the earth is related to what we can see at the earth surface. We get information about the interior of the earth from such things as earthquakes, volcanic eruptions and from deep mines. For instance, people who work in deep mines, like the gold mines in South Africa, have noted that temperatures underground are higher than temperatures on the ground surface. You have probably seen a model of the earth called a globe. The earth is shaped like a sphere, a round shape that is slightly flattened at the poles. A cut through the earth will show three circular layers called the crust, the mantle and the core. The distance from the surface of the earth to its inner most center is about 6400 kilometers. As we go deeper and deeper into the earth, the temperature and pressure increase.

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