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LIVING IN THE ENVIRONMENT, 18e G. TYLER MILLER • SCOTT E. SPOOLMAN Rocks and Soil ©©Cengage CengageLearning Learning2015 2015 What Are Minerals and Rocks? • Mineral – Naturally occurring compound that exists as a crystalline solid • Mineral resource – Concentration that we can extract and process into raw materials • Rock – Solid combination of one or more minerals © Cengage Learning 2015 What Are Minerals and Rocks? • Sedimentary rock – Made of sediments • Dead plant/animal remains (fossils!) • Tiny particles of weathered and eroded rocks – The sediment gets turned into rock by • Being buried/compacted by weight or rocks • Being cemented together by materials that have been dissolved in water © Cengage Learning 2015 What Are Minerals and Rocks? • Metamorphic rock – Existing rock subjected to high temperatures, pressures, fluids, or a combination – Pressure and heat can come from being buried deep in the earth or from proximity to magma © Cengage Learning 2015 • Igneous rock – Intense heat and pressure, magma wells up from the earth’s mantle, cools & hardens Examples of Igneous Rocks • Pumice • Obsidian • Basalt • Other examples include: Diabase, Diorite, Gabbro, Granite, Rhyolite, Scoria © Cengage Learning 2015 Examples of Sedimentary Rocks • Shale = silt particles • Sandstone = sand particles • Limestone = calcium carbonate or calcite (shells of marine organisms) • Other examples include: Breccia, Conglomerate © Cengage Learning 2015 Examples of Metamorphic Rocks • Marble • Slate • Gneiss • Other examples include: Quartzite, Schist, Serpentinite © Cengage Learning 2015 Earth’s Rocks Are Recycled Very Slowly • Rock cycle – Rocks are recycled over millions of years – Erosion, melting, and metamorphism – Slowest of earth’s cycle processes © Cengage Learning 2015 External Earth’s Processes: Can Lead to Soil • Weathering-breakdown of solid rock – Mechanical (Physical) weathering • Frost Wedging, freeze-thaw cycle – Chemical Weathering • Oxidation (losing/gaining e-) • Hydrolysis (splitting of water) • Erosion-process by which earth particles are moved from one place & deposited in another – Wind -Ice – Water -Gravity © Cengage Learning 2015 Soil is the Foundation of Life on Land • Mixture of eroded rock, mineral nutrients, decaying organic matter, water, air, humus (microorganisms, decaying organic material) & living organisms © Cengage Learning 2015 • Formation begins when – Bedrock is slowly broken into fragments/particles by physical, chemical & biological processes Soil is the Foundation of Life on Land • Key component of earth’s natural capital • Supplies most of nutrients needed for plant growth • Purifies & stores water • Organisms living in it remove CO2 from atmosphere & store it as organic carbon compounds – Helps control earth’s climate © Cengage Learning 2015 Mature Soils • Contain horizontal layers “horizons” • O horizon • A horizon • B horizon • C horizon • Bedrock (base parent material) © Cengage Learning 2015 The Horizons of Soil • “O horizon” – Leaf litter • “A horizon” – topsoil – Upper layer • Contain bacteria, fungi, earthworms, small insects • Decomposers break down compounds into “humus” & inorganic materials © Cengage Learning 2015 The Horizons of Soil • “B Horizon” – subsoil • “C horizon” – Parent material • Most of inorganic matterbroken down rock containing varying mixtures of sand, silt, clay, gravel • Underneath “C” is the bedrock © Cengage Learning 2015 The Horizons of Soil • Spaces (“pores”) contain air or water • As long as “O/A” are anchored by vegetation, the soil layers as a whole act as a sponge, storing water & nutrients! • Topsoil-renewable resource but very slow replenishment rate! (1 cm takes 100s of years to form!) © Cengage Learning 2015 Soil Properties 1. Water 2. Texture: the way the soil feels – Infiltration – Leaching – Porosity: amount of pore spaces – Permeability: ability to transmit fluids Water Water − Depends on amount of each sized particlestermed soil fraction − Sand: larges, gritty − Silt: medium, soft, silky, floury − Clay: small, sticky, hard to squeeze, greatest surface area High permeability © Cengage Learning 2015 Low permeability Soil Properties 100%clay 0 80 clay 60 Increasing percentage clay san dy clay sandy clay loam 40 loamy sand sand clay loam loam sandy loam Increasing percentage silt silty clay 40 20 20 60 silty clay loam silty loam 0 100%sand 80 60 40 20 © Cengage Learning 2015 Increasing percentage sand 80 silt 100%silt Gravel 2-64 mm Sand 0.05-2 mm Silt 0.002-0.05 mm Clay less than 0.002 mm Soil Properties 3. pH − Influences uptake of nutrients by plants © Cengage Learning 2015 4. Fertility − 20 minerals needed for plant growth − Major nutrients = nitrogen, phosphorus & potassium Topsoil Erosion Is a Serious Problem in Parts of the World • Soil erosion – Movement of soil by wind and water – Natural causes – Human causes • Two major harmful effects of soil erosion – Loss of soil fertility – Water pollution © Cengage Learning 2015 Drought and Human Activities Are Degrading Drylands • Desertification – Productive potential of topsoil falls by 10% or more – Prolonged drought, human activities • Human agriculture accelerates desertification • Dust bowl – Severe wind erosion of topsoil – Combination of poor cultivation practices & prolonged drought © Cengage Learning 2015 Excessive Irrigation Has Serious Consequences • Soil salinization – Gradual accumulation of salts in the soil from irrigation water – Lowers crop yields and can even kill plants – Affects 10% of world croplands • Waterlogging – Saturation of soil with irrigation water or excess precipitation – Water table rises close to the © Cengage Learning 2015 surface Many Farmers Are Reducing Soil Erosion • Soil conservation – Terracing – Contour planting – Strip cropping with cover crop – Alley cropping, agroforestry – Windbreaks or shelterbelts – Conservation-tillage farming • Identify erosion hotspots © Cengage Learning 2015 We Can Restore Soil Fertility • Organic fertilizer – Animal manure – Green manure – Compost • Manufactured inorganic fertilizer – Nitrogen, phosphorus, and calcium • Crop rotation © Cengage Learning 2015 US Legislation • Soil Conservation Act of 1935: law organized the Soil Conservation Service which is now called the Natural Resources Council • Food Security Act or Farm Bill of 1985: Law required US farmers to control erosion on land that was subject to large amounts of soil loss – If they failed to do so, lost government price © Cengage Learning 2015 supports for product