Module 5
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describe the process of weathering and sediment production, and distinguish between physical and chemical weathering.
Weathering produces sediment by: Breaking down larger rocks into smaller fragments (sand, silt, clay, gravel). Altering mineral composition, producing new minerals or soluble ions that can be carried away by water.
provide examples of physical weathering.
• Physical (Mechanical) Weathering This involves the breaking of rocks into smaller pieces without changing their chemical composition. Common mechanisms include: Frost wedging: Water enters cracks, freezes, expands, and breaks the rock. Thermal expansion/contraction: Temperature changes cause rocks to expand and contract, creating fractures. Exfoliation: Layers peel off due to pressure release from overlying rock removal. Abrasion: Rocks are worn down by friction from wind, water, or ice. Biological activity: Roots or burrowing animals physically break rock apart.
explain what factors control the rate of weathering.
• Climate • Temperature: High temperatures accelerate chemical reactions, increasing chemical weathering rates. Extreme temperature fluctuations enhance physical weathering like thermal expansion. Moisture (precipitation and humidity): Regions with high rainfall experience faster chemical weathering. Dry climates favor physical weathering (e.g., wind abrasion, freeze-thaw cycles in deserts). • Rock type • Surface Area • Topography • Biological activity
explain the difference between sediment and soil, and describe how soil forms and why conserving it has become a challenge.
All soil contains sediment, but soil is living and layered, capable of supporting plants and ecosystems, while sediment is just broken-down rock material. Soil is a finite and vital resource, but its conservation is increasingly difficult due to: Erosion: Water and wind remove topsoil, especially on slopes or overplowed fields. Deforestation: Removing vegetation leaves soil exposed to rain and wind, accelerating loss. Agricultural Practices: Intensive monoculture, overgrazing, and tilling degrade soil structure and deplete nutrients. Urbanization: Soil is often covered by concrete or contaminated by pollution, preventing natural soil functions. Climate Change: Changes in rainfall patterns, droughts, and floods can degrade soil quality and accelerate erosion.
explain how sediment changes as it moves from its source toward its place of final deposition.
Gets smaller, better sorted, and more rounded
outline the stages involved in the transformation of sediment into clastic sedimentary rock, and recognize the major types of clastic sedimentary rocks.
• Breakdown of rock to form sediment • Transportation of sediment • Deposition of sediment • Lithification
provide examples of biochemical, chemical, and organic sedimentary rocks, and discuss how each forms.
Biochemical Sedimentary Rocks Formed from the accumulation of materials produced by living organisms, often involving the skeletons or shells of marine organisms. Chemical Sedimentary Rocks Formed from the precipitation of minerals from water, usually from evaporating seawater or lakes, without direct biological activity. Organic Sedimentary Rocks Formed from accumulated organic material, mainly plant remains, rather than inorganic minerals.
relate examples of sedimentary structures to the environments in which they develop.
associate kinds of sedimentary strata and structures with specific depositional settings.
like the wavy river bed
explain why layers of marine strata lie beneath what is now dry land in continental interiors, and why the thickness of sedimentary strata varies from place to place.
provide examples of chemical weathering
This involves chemical alteration of minerals, transforming them into new minerals or soluble ions. Common chemical processes include: Hydrolysis: Reaction of minerals with water, e.g., feldspar → clay minerals. Oxidation: Reaction of minerals with oxygen, e.g., iron → iron oxide (rust). Dissolution: Soluble minerals like calcite dissolve in water (often aided by carbonic acid from CO₂). Hydration: Minerals absorb water and expand, weakening rock.