Physical and biological agents, such as wind, running water, temperature changes, and living organisms, perpetually modify the Earth’s crust, changing its upper surface into products that are more nearly in equilibrium with the atmosphere, the hydrosphere, and the biosphere. Earth scientists sum up all processes through which these alterations take place under the collective term weathering. One speaks of mechanical weathering in case the dominant forces are mainly mechanical such as the eroding action of running water, the abrading action of stream load or the physical action of wind and severe temperature fluctuations. Similarly, one speaks of biological weathering when the forces producing changes are directly or indirectly related to living organisms. Of these, we can mention several examples such as the action of burrowing animals, penetration forces of plant roots, and the destructive action of algae, bacteria, and their acid-producing symbiotic community of the lichens or simply the destructive action of man, who continuously disturbs the Earth’s crust through various activities.
KeywordsSoil Formation Colloidal Silica Chemical Weathering Organic Debris Iron Silicate
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