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Lesson: Soils Weathering corresponding to Chapter 6: Soils, Weathering, Erosion

Summary of Important Concepts. Soil is a layer of weathered rock, minerals, and organic matter at the earth's surface that supports plant life. The main factors that determine the characteristics of a soil are climate (mainly temperature and rainfall), topography, type of parent rock material, organic activity, and the amount of time that the soil has been forming. Soil forms from regolith - broken up rock material at the earth's surface. Soil forms as regolith undergoes weathering - the30486

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Lesson: Soils Weathering corresponding to Chapter 6: Soils, Weathering, Erosion

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    2. Summary of Important Concepts

    3. Summary of Important Concepts, continued

    4. Summary of Important Concepts, continued

    5. Summary of Important Concepts, continued

    10. Physical Weathering and Chemical Weathering work hand in hand: Physical disintegration creates more surface area for chemical processes to act upon minerals. Smaller pieces have a greater surface area: volume so they are easily attacked by chemical weathering.

    11. Role of Water. 1. Universal Solvent: Right shows a water molecule. Note the slightly positive charge on one end and slightly negative charge on the other. Although it is electrically neutral, the slight difference in charge on either side makes the molecule easily dissolve weakly (ionic) bound minerals. 2. Hydrolysis: Water can split to form H+ and OH- ions. The number of H+ ions in a solution determines the pH of the solution where pH=1 is acidic with many H+ ions, 7 is neutral and pH=14 Basic with few H+ ions. 3. Expands When Frozen; densest at 4oC.

    12. Physical Weathering: Physically disintegrating but not changing chemically.

    14. Frost Wedging, very effective at breaking up rocks. Only in climates with frequent freeze/thaw cycles.

    15. Abrasion: The longer sediments or rocks or pebbles are in transit, the more bumping and abrading it undergoes. Right: Well rounded sediments indicate LONG TRANSPORTATION TIME.

    16. Pressure Release/Unloading: Intrusive rocks form and are stable under pressure. Once the pressure (layers of rock removed) is relieved, the rock expands and cracks.

    17. Biological Weathering: plant/tree roots can be very powerful. Root systems can squeeze through cracks, and as the plant grows, enlarge the cracks.

    18. Biological weathering by lichens growing on rocks! Metabolic byproducts of the lichen can chemically weather the minerals.

    19. Chemical Weathering: breakdown of rock by chemical reactions that occur when rock and mineral matter interact with water and air.

    22. Stone Mountain, Georgia: made of granite and granite is made of different minerals, of which have different silicate structure and thus different stabilities. Certain minerals are more susceptible to chemical weathering. Preferential weathering forms little divots in Stone Mountain.

    23. Chemical Weathering of Limestone: easy to do so long as you have some ACID (calcite remember) in the rain. Marble (limestone is the parent) headstones dont last as long as granite headstones (or buildings for that matter).

    25. Controls on Weathering Time Climate (Influences both chemical and physical weathering). Parent Rock Chemical Composition (Silicate minerals higher on Bowens reaction series are weaker).

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