Soil forms through the interaction of the major soil-forming factors--parent material, climate, vegetation and animal life, relief, and time. Relief, or the shape of the landscape, influences soil formation, mainly through its effect on drainage and erosion, and partly through variations in exposure to the sun and wind and air drainage. Under the influence of solar radiation, the rocks heat up and expand. The further process is discussed below:
- At night, these cool down and contract. Since all parts of the rocks do not expand and contract at the same rate, cracks appear in the rocks and ultimately the large rocks break up into smaller pieces.
- Exposure to the sun is closely related to temperature which also has a profound effect on weathering. Warm temperatures, coupled with high moisture, will increase weathering processes. Therefore, in the warm, wet climates of the tropics, it is typical to have well-developed, highly weathered soils.
- In places with extreme climatic conditions, such as the Arctic Circle or the arid region, the rocks are subjected to sudden expansion and contraction, which results in the loosening of their particles and an increase in the air content.
- Over time, the effect significantly reduces a rock to loosen soil. The rocks swell when they are wet and shrink back when dry. Regular wetting and drying of rocks result in the loosening of their grains. Therefore, the sun has an important role to play in the formation of soil.
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