This quote describes soil and its importance quite effectively. Well, soil is defined as the naturally occurring, unconsolidated mineral or organic material at the surface of the earth that is capable of supporting plant growth. Soil is synonymous with the word 'earth', the word from which our planet derives its name. In the following sections of this Buzzle article, we give you some basic information about soil as well as some interesting facts about it. ✦ Clay, silt, and sand are the three types of soil. Most soils are a blend of all three types. The texture and appearance of soil depends on the content of each of these in it. ✦ Sand is mainly granular and is composed of rock particles and minerals. ✦ Clay has fine-grained minerals and a high water content. ✦ Silt is a granular material derived from rock. It may occur as a deposition in water. It is also known as stone-dust. ✦ Soil holds 0.01% of the Earth's water. ✦ Soil is a composition of 49% oxygen, 33% silicone, 7% aluminum, 4% iron, and 2% carbon. ✦ Air and water make up 50% of the soil. The porous phase of soil stores them. ✦ Minerals and organic matter make up the rest of soil. They are a part of its solid phase. ✦ Soil formation is a lengthy process. It forms by the process of physical or chemical weathering of rocks. ✦ The study of processes that lead to formation of soil is known as pedogenesis. Russian geologist Vasily Dokuchaev pioneered this study and found that soil is formed over time as a result of climatic, mineral, and biological processes. ✦ Climate, relief, organisms, parent material, and time, abbreviated as CROPT are the factors that influence the evolution of soil. ✦ Precipitation and temperature are the climatic factors that affect soil formation. ✦ Relief, which can also be called topography is the elevation or slope of a terrain which decides the precipitation or runoff and the erosion in that area. ✦ The movement of organisms in soil causes the movement of air and nutrients. The burrowing by animals causes mixing of soils and aeration. Earthworms recycle nutrients, thus making the soil richer. Plants prevent soil erosion, provide it with shade, and cause the exchange of nutrients between the soil and the atmosphere. Microorganisms in soil help in the breakdown of organic matter. Decaying of plants and animals helps in the formation of soil. Human activities lead to erosion of soil and also bring about changes in its fertility. Thus, organisms affect soil formation and evolution. ✦ Parent material includes the minerals from which soil forms. ✦ Climate, relief, organisms, and parent material, together lead to changes in soil over time, and depending on the interplay of these factors, soil forms and evolves over a certain span of time. This makes time an important factor influencing soil formation. ✦ Soil can be divided into layers, where the physical features, age, and composition of each layer is different from the other. Each such horizontal layer of soil is known as a soil horizon. ✦ The topmost layer is called topsoil. It contains high amounts of humus and microorganisms. Biological activity occurs mostly in this layer. It is from this layer that plants derive their nutrients. ✦ Not much humus is present in the layer below this. ✦ The process of leaching brings down the minerals from the upper layers of soil to the layers below. ✦ The bottom-most layer of soil consists of withered rock. ✦ All the soil on Earth is younger than the Cenozoic. Very little of it is older than the Pleistocene. ✦ Soil influences many areas of our lives. It is an integral part of our ecosystem. The composition of soil in an area has a direct effect on the plant and animal life there. ✦ It takes more than 500 years to form 2 centimeters of topsoil. ✦ Ten tons of topsoil spread evenly over one hectare land comes out to be as thick as one Euro coin. ✦ A fully functional soil holds 3750 tons of water per hectare, thus reducing the risk of floods. It holds pollutants to a certain extent. Soil stores around 10% of the emissions of carbon dioxide. ✦ Just one gram of soil contains 5000 to 7000 different species of bacteria. A spoonful of soil can hold a substantial number of living beings. ✦ Scientists have found 10,000 types of soil in Europe and about 70,000 types of soil in the United States. ✦ 75% of the earth's crust is composed of silica and oxygen. ✦ Heterotrophic organisms in soil feed on the carbonaceous material therein. Through their respiration, the soil's carbon content is returned to the atmosphere. ✦ Soil converts dead organic matter into nutrients which are made available to the plants and animals in the soil. ✦ Most nutrients in soil come from the minerals. But nitrogen comes from the nitrogen-fixing bacteria that convert atmospheric nitrogen into nitrogen compounds like ammonium and nitrogen dioxide that the plants can use. ✦ The porosity of soil is essential for ventilation and the absorption and holding of water which is used by plants. The pores allow air and water movement which is essential for the survival of life in soil. Compaction of soil results in the reduction of pore space due to which air and water cannot reach the plant roots and other living organisms in soil. ✦ It is in the soil that crops grow and we can thereby obtain food. Many of the antibiotics that stand as remedies for infections, were obtained from microorganisms in the soil. ✦ As a matter of fact, agriculture remains to be the only essential industry. ✦ Soil is a non-renewable natural resource. This should make us think of how much we value it. Damage to soil, a degradation of its quality, or land pollution can disturb nature's balance and prove to be a threat to life. ✦ Some animals consume soil. Chimpanzees in Uganda were found to eat soil. Red-and-green macaws eat clay from riverbanks. This lets them use nutrients in harmful foods. The practice of eating soil-like substances is seen in humans too, typically in those from rural areas for recreational or religious reasons. It may be linked with the eating disorder called pica. The practice of eating soil-like substances is called geophagia. Soil in its various forms, plays a major role in our lives. In the words of the Greek philosopher and poet Xenophanes, "For all things come from earth, and all things end by becoming earth."