Soil as a Part of the Lithosphere

Abstract

The lithosphere is the upper part of the earth. It includes the crust and the solid portion of the mantle. Lithosphere interacts with atmosphere, hydrosphere, and biosphere and produces the pedosphere (the soil with its biotic and abiotic components). The lithosphere contains rocks, minerals, and soils. It is made up with more than 100 chemical elements, but most of them are rare. Only eight elements—oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg)—constitute more than 99 % of its volume. In the earth’s crust, these elements generally form crystalline solid compounds of definite chemical composition which are known as minerals. Chemically, minerals may be sulfides, sulfosalts, oxides and hydroxides, halides, carbonates, nitrates, borates, sulfates, phosphates, and silicates. Most rock-forming minerals are, however, aluminosilicates of Ca, Mg, Na, and K because these elements are most abundant. Minerals are aggregated into rocks. Rocks may be igneous, sedimentary, and metamorphic. Igneous rocks are formed by solidification of magma or lava, sedimentary rocks are formed by lithification of sediments or by precipitation from solution and consolidation of remnants of plants and animals, and metamorphic rocks are formed from preexisting rocks by the change temperature and pressure in the solid state. By the action of natural forces over geological time, rocks and minerals are disintegrated and decomposed into new minerals and new compounds such as salts, acids, bases, and soluble substances. The processes are collectively known as weathering. However, the effects of rocks and minerals on mature soils are usually temporary. Their effects are profound in young and immature soils. Eventually, similar soils may develop from dissimilar rocks depending on other soil-forming factors.