Gas, rock and soil are the surface materials that make up the earth. We can find the corresponding specimens and observe them carefully. Through different sources, scientists have been able to synthesize a lot of evidence and draw a complete map of the earth structure.

Air is a mixture of three gases, 78% of which is nitrogen. Nitrogen is a very inert gas, which means that it is not easy to react with other substances. The air contains about 2 1% oxygen, which is an indispensable gas for human breathing. There is also a small amount of hydrogen, a certain amount of rare gas and a certain amount of carbon dioxide, which are all gases needed by plants.

Almost 99% of the rocks on the earth's surface are composed of eight basic substances or elements. These elements are oxygen and silicon, which are important raw materials for glass production. The aluminum, iron, calcium and sodium, potassium and magnesium contained in salt needed by human bones. Everything belongs to metals except oxygen and silicon.