EROSION: It is a process in which the top fertile layer of soil is lost by the natural forces. Due to soil erosion, the soil becomes less fertile.Causes of soil erosion:Wind: When strong winds blow, the topsoil along with the organic matter is carried away by the wind. This happens more often when the land is not covered with grass or plants.Water: When it rains in the hilly areas, the soil gets washed away towards the plains. The running water deposits the mineral-rich soil in the riverbed.Overgrazing: When cattle are allowed to graze on the same field repeatedly, all the available grass, including the roots are eaten by them. This makes the topsoil vulnerable to wind and flowing water, LEADING to soil erosion.Deforestation: Humans have taken land from the forest to cultivate in order to feed the ever-increasing population and to build houses, industries, etc. Cutting down of TREES on a large scale for these purposes is known as deforestation.Afforestation: It is a process of planting trees on the lands to create a forest. It maintains the BIODIVERSITY and ecological balances.It prevents global warming, pollution and erosion of soil. It purifies the environment and REDUCES the level of carbon dioxide.The roots of trees hold the soil together, thus preventing the soil from getting uprooted. When large areas of the forest are cleared, the topsoil gets eroded by wind and flowing water.Soil erosion can be prevented by planting trees i.e Afforestation.