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Download Rocks, Soil AP Env Sci Class 14 Dr. Mike Sowa
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Transcript
Rocks to Soil AP Env Sci 2011-2012 Earth’s Surface is Constantly Changing • Internal Processes: elevating parts of Earth’s surface – Mountain Building – Volcanic Activity • External Processes: breaking rock and moving it to lower elevation – Weathering – Mass Wasting – Erosion • Weathering Processes Make Soil Soil Formation • Soil – several ways to define: – Unconsolidated material overlying bedrock – * Material capable of supporting plant growth * • Soil is produced by weathering – Physical, Chemical, Biological Processes – Climate, topography, source material composition, and time are factors Mechanical Weathering • Large pieces are broken up into smaller pieces – Frost Wedging – Biological Activity • Processes do not work alone! • Chemical processes attack exposed surface, so: – smaller pieces -> more surface area exposed – more exposure -> more chemical attack Frost wedging of Diabase Boulders at Sourlands Michael Hambrey 2. Mech. weathering – Biological activity Biological activity does mechanical work and introduces chemicals to rock Chemical Weathering • What does the Weathering? – Water, with small quantities of dissolved components – ex. CO2 (forms carbonic acid) -> H2CO3 – ex. O2 (oxidizer) • Crust is made up primarily of silicate minerals • Fate of Most Abundant Elements: – Sodium, Calcium, Potassium, Magnesium – form ions – Iron – oxidizes to iron oxides (red/yellow) – Aluminum, Silicon, Oxygen – form clays Example: Granite • Granite: mainly quartz & potassium feldspar (KAlSi3O8) • Potassium Feldspar reacts with Carbonic Acid: 2(KAlSi3O8) + 2(H2CO3) + H2O -> Al2Si2O5(OH)4 + 2K+ + 2HCO3- +4SiO2 • Product is clay mineral and ions in solution • Quartz is resistant to chemical weathering • Quartz (sand) is transported to sea or elsewhere 3. Chemical weathering Breakdown by Acids Natural sources: Decaying organic matter makes CO2. CO2 + water carbonic acid Anthropogenic source (human impact): SO2 and NOx create acids when combined with water acid rain Factors Affecting Rate of Weathering • Exposed Surface Area • Rock Characteristics – Mineral composition – Solubility – Cracks, etc • Climate – Temperature – Moisture – Warm temperature/high moisture favors chemical weathering Weathering rates of gravestones (Kingston) Marble Slate 1837 1817 What is Soil? • Soil is a combination of mineral and organic matter, water, and air. • It is the part of the regolith (rock and mineral fragments produced by weathering) that supports the growth of plants 5% 25% water air 45% mineral 25% humus (organic) Characterizing Soil Texture: The Soil Triangle Let’s Practice…. Source: EID Soil: Big to Small • Sand: 2 to 0.2 mm • Silt: 0.02 to 0.002 mm • Clay: 0.002 mm and smaller You Need to Know the Soil Triangle: Why? • Texture impacts soil’s ability to retain and transmit air: – Larger particles have larger spaces between them – Packing -> loose = easily aerated (sand) • Texture impacts soil’s ability to retain and transmit water: – Surface area -> small particles have more SA/volume – Nutrients and water retained by surfaces • Sandy soils drain fast, dry out rapidly • Clay drains slowly • Texture affects “workability” (agriculture) • Loam soils supports plant life best Control of Soil Formation • Parent Material: Source of weathered mineral matter – Parent = Bedrock – residual soils – Parent = Sediment – transported soils • • • • Time: How Long? Climate: Temperature and Precipitation Plants and Animals: Source of organic matter Topography: – Steep slopes often poor soil – Bottomlands often poor drainage, much organic – Best: flat to undulating uplands Soil Profile Soil Profile • O Horizon: Loose and partly decayed organic matter • A Horizon: Mineral matter mixed with some humus • E Horizon: Light colored mineral particles. Zone of eluviation and leaching • B Horizon: Accumulation of clay transported from above • C Horizon: Partially altered parent material • Solum: O, A, E, and B layers. The “true soil” where soil formation processes are underway and plant and animal life exist. Soil and Plant Growth: Minerals, Water, Air • Minerals: – From Weathering – Lost by Leaching – Replaced by Fertilizer • Organic • Inorganic – Can you identify the three most important? Soil and Plant Growth: Minerals, Water, Air • Water: – Absorbed through roots – Lost through transpiration – Soil gains water through Infiltration – Soils retain water to varying degrees: WaterHolding Capacity Soil and Plant Growth: Minerals, Water, Air • Air: – Roots need air – Aeration of soil creates space for air to enter – Compaction has opposite effect Soil Gains and Losses • Gain Organic Matter: – Ample organic matter (humus) – Nutrients, infiltration and water-holding capacity, aeration all increase • Lose Organic Matter: – Humus loss (how?) – Nutrients, infiltration and water-holding capacity, aeration all decrease • Mineralization: Near Complete Loss of Organic Component!