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Transcript
Earth’s Resources: Soil What is soil? The outermost layer of the earth’s crust Made up of both organic (from living things) and inorganic materials. It’s divided into layers according to the ratio of organic to inorganic material at various depths It’s classified according to what kind of material you can find in a sample Layers of the soil The layers vary as to content The closer to the top, the more organic material you’ll find Leaves Sticks Dead animals (insects as well as larger critters) Finally, at the bottom, you will hit BEDROCK! Layers = HORIZONS The topmost layer, or O horizon, includes “litter” or detritus from formerly living things. The A horizon is the most valuable – It is the topsoil where plants get most of their nutrients. The decaying organic matter in this layer is called humus. Humus As living things (both dead plants and dead animals) decompose, their molecular components become available for new plants to take up as nutrients. This decayed material is called humus. Humus is mostly insoluble, so it remains in these upper layers of soil. It is very dark, nearly black in color. Human created humus is called compost! TOPSOIL Five tons of topsoil spread over an acre would only be as thick as a dime! It takes over 500 years for organic material to collect and decompose naturally to form only ONE INCH of topsoil! 5 to 10 tons of animal life can exist in an acre of topsoil! Layers = HORIZONS The E horizon is where the nutrients from the organic material (humus) begin to dissolve. The deepest of plants’ roots sometimes extend this far. Layers = HORIZONS The B horizon (aka subsoil) This layer contains a smaller amount of organic material. It has a heavy concetration of the minerals leached from the above layers. Layers = HORIZONS The C and R horizons are the underlying rock. C horizon is weathered and broken rock or regolith. Leached minerals may be found here. The R horizon is bedrock (almost solid crustal material.) Layers = Horizons Soil in different locations may or may not have all of these horizons For instance, in a construction zone, all of the topsoil may have been removed. Topsoil may have eroded through wind or water effects. Heavy earthquake or storm damage may have disrupted the existing layers Other components of soil Water – after rains or floods, water infiltrates the soil, carrying the nutrients to plant roots and into lower horizons Air – soil is composed of approximately 25% air, aided by the movement of worms and insects in the topsoil layers 5% living things – plant roots, worms, microorganisms make up part of the soil. Leaching After rain or other sorts of precipitation, water moves into the soil. This is called infiltration. As it moves from the topsoil layer into the subsoils and deeper, it dissolves inorganic minerals from the upper layers. This is called leaching. Minerals and other substances may be carried into groundwater supplies and thus into drinking water in this manner.