Soil—the thin, unconsolidated, vertically differentiated portion of the Earth's surface—is ubiquitous and often ignored despite its many important environmental and life-sustaining functions. Soil is necessary for the production of food, feed, and fiber products, and supports buildings, roads, and playing fields. Soil helps to safely dispose of and process biological and industrial wastes, and it purifies and filters water that may enter drinking water supplies. Usually, soil performs more than one of these roles simultaneously.