What is soil made of?

Soil is the topmost layer of our planet’s surface. It can vary in appearance, size, and composition. According to the size of the particles that make up the soil, it is customary to divide into silt, clay, sand and gravel.
Four main substances are distinguished in the composition of the soil:
1. Mineral base;
2. Organic matter;
3. Water;
4. Air.
But depending on what kind of specific soil we are talking about, all these substances can be combined in different proportions.
Also, the soil may contain various impurities (for example, iron).