Soil covers most of the surface of the Earth's land. It occurred after the erosion of rocks, due to strong winds, water, ice and due to the activity of living organisms. Soil is usually suitable for plants and small organisms to grow and live. However, human activities have altered the natural soil environment of many areas, making it hostile to organisms.
Humanity deposits many toxic substances under the ground. Most of those are radioactive materials, pesticides, heavy metals and other kind of poisonous wastes. Even if they are first deposited in lakes, rivers or the sea, waters transfer most of them in the soil, when the latter absorbs water. It happens the other way round as well, as chemicals within soil are transferred with the rain into marine ecosystems.
Soil contamination is as a serious problem as any other form of pollution, but it was discovered later than them. Although it is connected with water pollution, the procedure is slow, and at first not even plants show any difference to point out pollution. If not stopped in time, it leads to desertification and destruction of the whole ecosystem. Many species lose their habitat, face extinction, or accumulate toxic substances in their body and become infected and poisonous for their predators.