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Chapter: 11th 12th std standard Geography earth space Higher secondary school College Notes

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Weathering and Products of Weathering

Weathering is the breakdown and alteration of rocks and minerals at or near the Earth's surface into products that are more in equilibrium with the conditions found in that environment. Most rocks and minerals are formed deep within the Earth's crust where temperatures and pressures differ greatly from the surface.

Weathering : Weathering is the breakdown and alteration of rocks and minerals at or near the Earth's surface into products that are more in equilibrium with the conditions found in that environment. Most rocks and minerals are formed deep within the Earth's crust where temperatures and pressures differ greatly from the surface. Because the physical and chemical nature of materials formed in the Earth's interior are characteristically in disequilibrium with conditions occurring on the surface. Because of this disequilibrium, these materails are easily attacked, de-composed, and eroded by various chemical and physical surface processes.

 

The products of weathering are a major source of sediments for erosion and deposition. Many types of sedimentary rocks are composed of particles that have been weathered, eroded, transported, and terminally deposited in basins. 'Weathering also contributes to the formation of soil by providing mineral particles like sand, silt, and clay. Elements and compounds extracted from the rocks and minerals by weathering processes supply nutrients for plant uptake.

 

Products of Weathering : The process of weathering can result in the following three outcomes on rocks and minerals :

 

(1) The complete loss of particular atoms or compounds from the weathered surface.

 

(2) The addition of specific atoms or compounds to the weathered surface.

 

(3) A breakdown of one mass into two or more masses, with no chemical change in the mineral or rock.

Theresidue of weathering consists of chemically altered and unaltered materials. The most common unaltered residue is quartz. Many of the chemically altered products of weathering become very simple small compounds or nutrient ions. These residues can then be dissolved or transported by water, released to the atmoshpere as a gas, or taken up by plants for nutrition. Some of the products of weathering, less resistant alumino-silicate minerals, become clay particles. Other altered materials are reconstituted by sedimentary or metamorphic processes to become new rocks and minerals. These rocks may have gone through several cycles, and may have undergone metamorphism or sedimentation before they finally became soil. It takes hundred years to form one centimeter of soil from the weathering of rocks. In a few places, this soil is only a few centimeters deep; in other places it is 20 to 30 centimeters in depth.

 

Soils are the unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants. Soil particles are generally classified according to size; that is, sand as large particles, silt as medium and clay as fine. Particles larger than sand are classified as gravel and are large enough to be identified as an individual rock.

 

Soil is essential for fixing the roots of plants and also provides the necessary nutrients, suitable temperature, and moisture for its growth. Soil maintains its fertility with the remains of decayed plants and animals. The growth of plants depends on the fertility of the soil. all living organisms depend on these plants. But human interference makes the soil infertile. If this continues, ultimately it will affect the 'soil - plant - organism' links and create negative impacts in the rock cycle. To enrich the soil, humans add natural and chemical fertilizers. Chemical fertilizers usually damage soil, partially because they eradicate the natural micro organisms.

 

Essentially, all life depends upon the soil. There can be no life without soil and no soil without life; they have evolved together. But we abuse soil because we regard it as a commodity belonging to us. When we consider soil as a community to which we belong, we may begin to use it with care and conserve it. Similarly, water is also an important natural resource. Major portion of this water is present in the oceans and sea.


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