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Soil is the uppermost layer of the earth's crust. It is bounded by rocks at the bottom and by vegetation and the atmosphere at the top. In order to really call it soil, four factors must always be present: Atmosphere (air), biosphere (living beings), hydrosphere (water) and lithosphere (rocks). Soil microorganisms provide other living organisms with important nutrients, are involved in the degradation of many substances and in soil formation. They make the soil healthy, moist and rich in nutrients.
Explanation for children: When we go outside in the garden, we stand on soil. Under the soil there is a layer of rock, and plants usually grow on it. Soil microorganisms provide other living organisms with important nutrients and are involved in the decomposition of many substances - they make the soil healthy, moist and full of nutrients.