There are really two question here. Not only What is the earth made of? but also ‘How do we know what the earth is made of?’ We candid out about the materials that make up the surface of our planet by simply taking samples of all the rocks and soils which are exposed and carefully examining them.
But the earth measures almost 6600 kilometers from the surface to its center. The deepest holes which man has been able to drill in his search for oil are a little over seven kilometers and the deepest mines still less.
An attempt was made by scientists from the United States of America to drill a whole right through the earth’s crust. They knew that the crust was at is thinnest under the oceans, but they soon discovered the enormous cost and the project were abandoned.
This attempt was called the ‘Mohole project’ in honor of a famous geologist called Mohorovicic. So how do we know what is in the innermost parts of our planet?
Scientists have been able to piece together evidence from a variety of sources to give a picture of the composition of the Earth as a whole but first, we should look at some of the more common materials of which the Earth is made.
Let us begin with the air we breathe. It can be shown quite easily that air is mainly a mixture of three gasses. There is about 78 percent of the total volume occupied by the gas nitrogen. Nitrogen is fairly inert which means that it does not easily combine with other materials in the chemical reaction but it is very important when it does combine because of the variety of substances formed that are so essential to life. These substances are the proteins.
There is about 21 percent of oxygen in the air. This is the gas which we need to breathe. There are also small amounts of argon, a number of rare gasses and some carbon dioxide is the gas which plants need.
Almost 99 percent of the Earth’s surface rocks is made up of eight basic substances or elements. These are:
- Silicon which is the important component of glass,
- Aluminum found in clays,
- Iron which you are very familiar with,
- Calcium which your need to form your ones,
- Sodium found in common salt
- Potassium and
Apart from oxygen and silicon all of these are metals. We shall look at the depths of the Earth in the next question.
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