(i) The earth’s crusty is dynamic, it moves vertically and horizontally. The differences in the internal forces operating within the earth’s crust which is responsible for the variation on the earth’s crust. The earth’s surface is continuous subjected to external forces included basically by energy. They are active through with different intensities. The earth’s surface is continuously subjected to external and internal pressure. The external forces are known as exogenic forces and the internal forces are called endogenic forces. The actions of exogenic forces result in wearing down of relief or elevations and filling up of basins/depressions on the earth surface. The endogenic forces continuously elevate or build up parts of earth’s surface. So variations remain as long as opposing actions of exogenic and endogenic forces continue.

(ii) Exogenic forces act on the surface of the earth. All these forces derive their energy from the sun. Sunlight causes air to move, water to evaporate, and ocean waves to rise. These moving waves like water, waves attack the solid surface and erode it and deposit at faraway places. Erosion involves acquisition and transportation of rock debris. The erosion and transportation of earth materials are brought about by the wind, running water, glaciers. The climate is decided by the energy of the sun.

All geomorphic processes derive their energy form the sun but the gravitational force of the earth is also responsible because it enables mobility.

(iii) Weathering is action of elements of weather and climate over earth materials and rocks. Physical and chemical processes are not independent of each other. They are inter-dependant. Physical weathering processes depend on some applied forces such as the gravitational force, stress water pressure controlled by wetting and drying cycles. While in chemical weathering processes like oxidation, hydration, reduction, act on the rocks to decompose, dissolver or erode them in small fragments by chemical reactions.

Chemical weathering process depends on the work of physical weathering process. The agents of physical weathering such as temperature change and freezing break the rocks and provide chemical weathering process. It makes the rocks decayed which are broken down by physical weathering processes.

(iv) The pre requisite of soil is weathering. It enables the rock particles to break into tiny granules or smaller fragments. Soil formation is responsible for the number of factors. Weathering is the first and prime important for soil formation. Then the colonisation of bacteria, lichen, mosses, and sheltering of other organisms in the soil help in formation of humus. Then other grasses, plants, twigs get mixed to it and make the soil fertile. As air gets into it, the soil gets nourished.

Soil forming factors control the formation of the soils. There are five steps:

• Parent material

• Topography

• Climate

• Biological activity

• Time

The climate and biological activities play very important role. The climatic elements involved in the soil development are moisture and temperature. Rain gives the soil moisture which makes the chemical and biological activities possible. Excess of water helps in the downward transportation of soil components through the soil and deposits the same below. Temperature acts in increasing or decreasing biological activity.

Biological activity includes the effects of vegetative cover, organisms and bacteria. The vegetative cover and organism help in adding organic matter, humus, moisture, nitrogen. Dead plants also provide humus. It makes the soil fertile.