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FIFTH EDITION

FIFTH EDITION. EARTH PORTRAIT of a PLANET. STEPHEN MARSHAK. Interlude B : A Surface Veneer: Sediments & Soils. In This Chapter, We Will Cover:. How rocks undergo change at or near the Earth’s surface due to weathering How weathering produces sediments

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FIFTH EDITION

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  1. FIFTH EDITION EARTH PORTRAIT of a PLANET STEPHEN MARSHAK Interlude B: A Surface Veneer: Sediments & Soils

  2. In This Chapter, We Will Cover: • How rocks undergo change at or near the Earth’s surface due to weathering • How weathering produces sediments • The difference between sediment and soil • Factors that affect the character and thickness of soil

  3. Sediment • Loose fragments of rock or minerals • Shells and shell fragments • Mineral crystals that precipitate from water

  4. Sediment • Produced by weathering • Physical and chemical breakdown of rock at Earth’s surface • Covers bedrock in various thickness • Can be transformed into soil through interaction with water and organisms

  5. Weathering • Combination of processes that corrode (weather) solid rock • Regolith • Layer of debris resulting from weathering

  6. Physical Weathering • Also called mechanical weathering • Breaks rocks into unconnected clasts • Clasts can vary in size • Processes can include: • Jointing, frost wedging, root wedging, thermal expansion

  7. Jointing • Joints • Natural cracks formed in rocks • Form due to: • Expansion of a rock undergoing exhumation • Cooling and contraction • Can have different shapes and orientations • Exfoliation • Occurs in exposed plutons • Jointing within exfoliation develop in layers parallel to the surface due to pressure release

  8. Jointing

  9. Frost Wedging • Water expands when frozen. • As water expands, it exerts a force on the surrounding rocks.

  10. Root Wedging • As roots grow, they exert a force on the surrounding rock.

  11. Salt Wedging • Occurs in arid climates and coastal areas • Salt dissolved in water precipitates. • Growing salt crystals exert a force on the surrounding rock. Salt wedging led to disintegration of gravestones in Whitby, England

  12. Thermal Expansion • Intense heat causes rock to expand; cooling causes rock to contract. • Repeated change causes enough force to break rock. • Occurs in deserts and due to forest fires

  13. When Animals Attack! • Another form of mechanical weathering • Animals burrow into rocks to build houses • Humans blast and excavate rock in mining, road construction, building foundations, etc.

  14. Chemical Weathering • Chemical reactions alter or destroy minerals when rock comes in contact with air and/or water. • Reactions differ depending on the minerals involved and type of liquid.

  15. Dissolution • Minerals that dissolve into water • Mostly affects carbonate rocks and salts

  16. Oxidation • Reactions during which an element loses electrons • Usually occurs when elements combine with oxygen • Common in iron-bearing minerals

  17. Hydrolysis • Water chemically reacts with minerals to form other minerals. • Common in feldspars and other silicate minerals • Hydration is the absorption of water into a mineral's crystal structure. • Causes expansion that weakens rock

  18. Rate of Chemical Weathering • Not all minerals chemically weather at the same rate

  19. Physical and Chemical Weathering • Work together to: • Increase surface area (physical). • Dissolve minerals and cements (chemical). • Alter hard minerals into soft minerals (chemical).

  20. Physical/Chemical Weathering

  21. Differential Weathering • Weathering occurs faster at edges and corners of a block than on a flat face.

  22. Differential Weathering • Different rocks in an outcrop weather at different rates.

  23. Soil • Rock or sediment modified by physical and chemical interaction with organic material and water that is capable of supporting plant life Soil forms on bedrock of chalk in southern England

  24. Soil Formation • Debris production • Interaction with water • Interaction with organics All of these produce unique layers called horizons that are seen in a soil profile.

  25. Soil Formation

  26. Soil Forming Factors • Climate and vegetation • Rainfall • Temperature • Vegetation can add or remove material

  27. Soil Forming Factors • Substrate composition • Mineral composition • Resistance to weathering

  28. Soil Forming Factors • Slope steepness and wetness • Regolith easily washes from steeper slopes. • Wetter soils contain more organic material. • Flat soils tend to hold more moisture and develop thicker soils.

  29. Soil Factor Factors • Time • Soils require time to develop. • Younger soils tend to be thinner.

  30. Soil Classification • Texture • Proportion of sand, silt, and clay • Structure • How many clumps (peds) form in the soil • Color • Reflects composition

  31. Soil Classification • United States uses the U.S. Comprehensive Soil Classification System

  32. Example Soils • Aridisol • Desert soil • Alfisol • Temperate climate soil • Oxisol • Tropical soil

  33. Example Soils

  34. Soils of the World

  35. Soil destruction • Nutrient removal • Soil erosion

  36. W. W. Norton & CompanyIndependent and Employee-Owned This concludes the Norton Media LibraryPowerPoint Slide Set for Interlude B Earth: Portrait of a Planet 5th Edition (2015) by Stephen Marshak PowerPoint slides prepared by Paul and Nathalie Brandes

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