What Major Layers Are Found in Mature Soils?
Soil is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, and billions of living organisms, most of them microscopic decomposers. Although soil is a potentially renewable resource, it is produced very slowly by the (1) weathering of rock, (2) deposit of sediments by erosion, and (3) decomposition of organic matter in dead organisms. Our lives and the lives of most other organisms depend on soil, especially topsoil. To a large extent all flesh is soil nutrients. Soil (1) supports plants that provide us with food, wood, paper, fiber, and medicines (Figure 8-4, p. 167), (2) helps purify the water we drink, and (3) helps decompose and recycle biodegradable wastes. Yet since the beginning of agriculture, human activities have led to rapid soil erosion, which can convert this renewable resource into a nonrenewable resource. Entire civilizations have collapsed because they mismanaged the topsoil that supported their populations. Mature soils are arrange
