What is Soil?
- Soil is not just dirt. It is the evolving layer of decomposing rock that covers parts of the Earth not covered by water or sand. Soil covers just 10 percent of the Earth's surface but produces all of the world's crops. The biology of soil and its physical properties are the subject of study for agronomists, soil and materials scientists as well as engineers.
- Soil is rock broken up by natural processes like earthquakes and volcanism and cultivated by rain, decaying plant and animal matter. The soils that cover the earth are actually self-perpetuating systems of mineral and organic materials.
- Soil texture is classified as "sand, "silt" or "clay," depending on the composition of minerals, organic compounds, its age and the physical processes that have acted upon it.
- Soil consists of three major layers: humus-rich topsoil, less fertile subsoil and horizon. The degree of organic matter decreases as the depth increases until the gravel and broken rock lacking any organic material that defines the horizon is reached just above bedrock of the area.
- The color of soil may be any shade of brown or gray to dark black, depending on the physical environment and biological history of the area.
- As plants and animals developed during the Pleistocene period, the rocky crust of the planet began to break down.
- Physical movements of tectonic plates, volcanism and the movement of water all began to wear down rock into gravel, then sand.
- In areas where plant and animal life flourished, organic matter worked into the soil,