About 4.55 billion years ago, the earth was a hot planet made of molten matter. After about 65.438+0.5 billion years, the earth's surface gradually cooled, forming various rocks. In the next time, under the action of external forces such as sun, water, glacier, gravity and wind, the physical and chemical properties of these rocks will change to varying degrees, and then the weathering crust with loose structure will be formed. The material in the weathering crust is the main material source of the earth's soil, and a small part is dust from the universe.
If you don't believe me, you can zoom in on a pile of soil dozens of times and observe it. Then you will find that the soil is actually composed of many very small gravel, which is the result of weathering of rocks on the earth's surface. However, these substances can't be called soil, and they can be found everywhere on Mars and the moon. This is because the soil we are talking about is a loose material layer, which has certain fertility on the surface, and the tiny substances produced after rock weathering have no fertility.
Why is the soil fertile? The answer is actually that there is another substance in the soil, humus. Humus is a gelatinous substance, usually dark brown or black, which is rich in carbon, nitrogen, oxygen, hydrogen, phosphorus, sulfur and other essential elements for higher plants. It is the main source of soil fertility, and more than half of the organic matter in the soil is humus. In addition, humus is a good substance, which can bind loose sand together and change too many binding substances.
Is the question of how soil is formed unique to the earth? That's all for today.