(i) (d) Erosion
(ii) (b) Clay
(i) The earth's crust is dynamic and ever-changing. All changes take place under the influence of certain forces working continuously within the earth as well as over the surface of the earth. The forces working over the earth's surface are known as exogenic forces, while those working within the earth are called endogenic forces. The exogenic forces cause degradation of relief of elevations and aggradations of basins on the earth's surface. The phenomenon of wearing down of relief variations of the surface of the earth by exogenic forces is known as gradation. Endogenic forces working inside the earth bring about the variations in the surface relief. It may be sudden forces like earthquakes, volcanoes, etc., in general, the endogenic forces are mainly land hurtling forces and exogenic forces are mainly land wearing forces.
(ii) Exogenic forces act on the surface of the earth. All exogenic forces such as weathering and denudation derive their energy from the sun. Sunlight causes air to move, water to evaporate, and ocean waves to rise. These moving fluids like water, wind and waves, etc., attack the solid surface, eroding it, carrying the broken pieces far away, and depositing them to fill low places in the landscape. Weathering is a process of the breaking of rocks by static agents of weather. In this process, the rocks are disintegrated by physical forces and decomposed by chemical action. Agents of physical weathering such as insulation, frost, etc., wholly depend upon energy derived from the sun. The agents of denudation like a river, glacier, wind, sea waves, etc., also derive their energy from the sun.
(iii) Weathering is the action of elements of weather and climate over earth materials. Physical and chemical weathering processes are not independent of each other, rather work of agents of physical and chemical weathering are interdependent. Chemical weathering is brought about by oxidation, carbonation, hydration and solution. The agents of physical weathering, like unloading and expansion, temperature changes and expansion, freezing, thawing and frost weathering, and salt weathering, easily break these decayed and decomposed rocks. Chemical weathering depends upon the work of physical weathering because physical weathering prepares the ground for agents of chemical weathering to work. For example, agents of physical weathering like the variation in temperature, freezing, thawing and frost wedging, salt weathering, etc., break the rocks and agents of chemical weathering can easily work on them.
(iv) Soil is a dynamic medium in which many chemical, physical, and biological activities going on constantly. The process of soil formation begins with the breaking of rocks into small pieces by various agents of weathering and erosion. Animals and insects with microorganism like bacteria also form organic matter. There is air in the open spaces within the soil containing more of carbon dioxide and also oxygen and nitrogen.
Factors of Soil Formation: Five basic factors control the formation of soils are parent material; topography; climate; biological activity; and time.
The role of climate and biological activity are followings:
The climate of an area is a major active factor in soil formation. In dry climates, because of high temperature, evaporation exceeds precipitation and hence groundwater is brought up to the surface by capillary action and in the process, the water evaporates leaving behind salts in the soil.
The biological activity includes the effect of vegetation, bacteria, and animals. Dead plants provide humus, which increases soils’ fertility. Burrowing animals like ants, rodents, termites, etc., also help in mixing and creating new contacts between air, water and minerals in the earth materials.
(i) Weathering processes are responsible for breaking down the rocks into smaller fragments. Biomes and biodiversity is a result of forests and forests depend upon the depth of weathering mantles.
(ii) Mass movements transfer the mass of rock debris down the slopes under the direct influence of gravity. These include creep, flow, slide, and fall.
(iii) Weathering, mass movements, erosion and transportation as well as deposition are the main mobile and mighty exogamic geomorphic agents. All these agents bring geomorphic changes on the surface of the earth.
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