How Soil Is Formed.doc - How Soil Is Formed Background...

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How Soil Is Formed Background Information Soil is a mixture of weathered rock particles and decayed organic matter. The relative amounts of particle sizes of the components determine the physical characteristics of the soil. The first step in this soil forming process is the weathering of rocks lying at or near the surface of earth. Several of the processes involved are: 1. Erosion – moving water, especially water carrying sand and silt particles, causing some breakdown of rocks. The water carries the particles along with great force, and acts like sand paper on the rock below. Small particles of rock are broken off and care carried by the water, sometimes to be deposited far away from their original location. The Grand Canyon is the most well known example of the erosion of rocks. 2. Wind – Wind is also an agent of rock breakdown, especially when it carries bots of grit and dust. These sandblast the rocks and cause formation of more rock fragments. 3. Geological Changes – The surface of the earth is in constant motion. As the separate pieces of crust move against and under each other, mountains, volcanoes, and huge rifts are formed. This is an extremely slow but powerful force in the formation of soil. 4. Glacial Activity – Glaciers played a significant role in the formation of most of the soil now present on the earth. During an Ice Age, glaciers move over hundreds of miles of rock. The pressure of thousands of feet of ice causes extensive breakdowns of the rocks. 5. Temperature Effects – Many rocks expand and contract with changes in temperature. Repeated expansion and contraction weakens the crystal structure of the rocks. This process accelerates as temperature changes become more rapid. As the outer surface of the rock expands and contracts with changes in air temperature, the inner portions of the rock stay at a more constant temperature. The outer layers of the rock separate and crumble away from the inner layers. 6. Water/Ice Changes – Water is able to enter the rock through many cracks formed by thermal expansion and contraction. The water may react with some of the minerals in the rock, weakening the crystal structure. If the temperature of the water drops below
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  • Fall '19
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