Geology
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Geology Earth’s Structure Name the zones of the earth Crust, mantle, core Now do it again with more detail Crust, lithosphere, asthenosphere, mantle, outer core, inner core 35 km (21 mi.) avg., 1,200˚C Crust 100 km (60 mi.) 200 km (120 mi.) Low-velocity zone Crust Mantle Lithosphere Solid 10 to 65km 2,900km (1,800 mi.) 3,700˚C Outer core (liquid) Core Inner core (solid) 100 km Asthenosphere (depth unknown) 200 km 5,200 km (3,100 mi.), 4,300˚C Fig. 10.2, p. 212 What is in each zone Core – mostly iron and a little nickel, inner solid and outer is liquid Mantle – mostly iron, silicon, oxygen, and magnesium, mostly rigid except near surface which is plastic (asthenosphere) Crust – mostly oxygen, silicon, aluminum, and iron (by weight) Convection below Heat from the formation of the earth combined with energy from radioactive decay gives way to convection currents of rock (very slow) or mantle plumes in which hot rock rises Plate tectonics The lithosphere is broken into many large plates which move due to convection currents within the asthenosphere Remember continental drift (Pangaea) Reykjanes Ridge EURASIAN PLATE JUAN DE FUCA PLATE CHINA SUBPLATE Transform fault PHILIPINE PLATE PACIFIC PLATE MidIndian Ocean Ridge Transform fault INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge NORTH AMERICAN PLATE COCOS PLATE East Pacific Rise MidAtlantic Ocean Ridge EURASIAN PLATE ANATOLIAN PLATE CARIBBEAN PLATE ARABIAN PLATE AFRICAN PLATE SOUTH AMERICAN PLATE Carlsberg Ridge AFRICAN PLATE Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Convergent plate boundaries Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( boundaries ) Plate motion at divergent plate boundaries Fig. 10.5b, p. 214 Plate boundaries Divergent – plates move apart, form mid ocean ridges Convergent – plates slam together, form largest mountains in the world Subduction is a type of convergent where one plate dives beneath another and usually creates trenches and volcanoes nearby Transverse – slide sideways past each other (San Andreas Fault) Trench Volcanic island arc Rising magma Subduction zone Lithosphere Asthenosphere Trench and volcanic island arc at a convergent plate boundary Fig. 10.6b, p. 215 Fracture zone Transform fault Lithosphere Asthenosphere Transform fault connecting two divergent plate boundaries Fig. 10.6c, p. 215 Lithosphere Asthenosphere Oceanic ridge at a divergent plate boundary Fig. 10.6a, p. 215 Oceanic crust (lithosphere) Abyssal Oceanic floor ridge Abyssal floor Abyssal plain Abyssal hills Trench Folded mountain belt Craton Volcanoes Continental shelf Continental slope Continental rise Abyssal plain Continental crust (lithosphere) Mantle (lithosphere) Mantle (lithosphere) Mantle (asthenosphere) Fig. 10.3, p. 213 Erosion and Weathering These are the external processes Erosion is the moving of rock material from one place to another (deposition) Weathering is the breaking down of rock by natural forces Ice wedging, rain, wind, gravity Chemical weathering, carbonic acid Lake Tidal flat Glacier Spits Stream Lagoon Dunes Shallow marine environment Barrier islands Delta Dunes Beach Shallow marine environment Volcanic island Coral reef Continental shelf Continental slope Continental rise Abyssal plain Deep-sea fan Fig. 10.7, p. 216 Rocks and minerals Mineral – an element or inorganic compound that occurs naturally, is solid, and has a regular crystalline internal structure Rock – type of music meant to be played loud, also any material that makes up a large, natural, continuous part of the earth’s crust Types of rock Igneous Granite, pumice, basalt Sedimentary Shale, sandstone, limestone (coral reef) Metamorphic Slate, marble, quartzite Transportation Deposition Sedimentary Rock Slate, sandstone, limestone Erosion Heat, pressure, stress Weathering EXTERNAL PROCESSES INTERNAL PROCESSES Igneous Rock Granite, pumice, basalt Cooling Heat, pressure Magma (molten rock) Metamorphic Rock Slate, marble, quartzite Melting Fig. 10.8, p. 217 Earthquake Fault – break in the lithosphere Focus – where the earthquake took place Epicenter – location above focus at surface Richter scale – used to measure magnitude, less than 3 is not felt, logarithmic scale, so each increase of 1 is a factor of 10 Minor < 5, damaging 5-6, destructive 6-7, major 7-8, great over 8 Aftershock – reduced shaking after original movement Volcano – it can happen here! Volcano - Wherever magma reaches the surface through a vent or fissure (also released are gases carbon dioxide, water vapor, hydrogen sulfide, ash, and other ejecta Mt. St. Helens – worst US volcano disaster Ring of fire – other than a song by Social D, this is the edge of the pacific plate where most volcanoes are located Soil Produced slowly (200-1000 years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter Soil horizons – separate zones within soil Soil profile – cross-section view of soil Horizons O horizon – surface litter A horizon – top soil, made up of inorganic particles (clay, silt, sand) and humus (organic particles from decomposed organisms) Dark topsoil is richer in nutrients Releases water and nutrients slowly Provides aeration to roots Healthy soil contains many nematodes and bacteria, fungi, etc. Oak tree Fern Word sorrel Lords and ladies Dog violet Earthworm Millipede Mole Honey fungus Grasses and small shrubs Organic debris Builds up Moss and lichen Rock fragments O horizon Leaf litter A horizon Topsoil Bedrock B horizon Subsoil Immature soil Regolith Young soil Pseudoscorpion C horizon Parent material Mite Nematode Actinomycetes Root system Red earth Springtail mite Mature soil Fungus Bacteria Fig. 10.12, p. 220 Poor topsoil Grey, yellow and red are not the colors of healthy topsoil Generally means that soil is lacking nutrients Best soil is called loam with equal parts sand, silt, clay and humus Leaching – dissolving and carrying nutrients (or pollutants) through soil into lower layers B – horizon and C - horizon B – Subsoil mostly broken down rock with little organic matter C- parent material broken down rock on top of the bedrock Soils Texture – relative amount of different sized particles present (sand, silt, clay) Porosity – volume of pore space in the soil Permeability – the ability of water to flow through the soil Water Water High permeability Low permeability Sandy soil Clay soil Soils Clay – high porosity, low permeability Sand – high permeability, low porosity Acidity is another factor Where rain is low, calcium and other alkaline compounds may build up (sulfur can be added – turns to sulfuric acid by bacteria) Forest litter leaf mold Acidic lightcolored humus Humus-mineral mixture Light-colored and acidic Light, grayishbrown, silt loam Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Acid litter and humus Humus and iron and aluminum compounds Dark brown Firm clay Deciduous Forest Soil (humid, mild climate) Coniferous Forest Soil (humid, cold climate) Fig. 10.15b, p. 223 Mosaic of closely packed pebbles, boulders Alkaline, dark, and rich in humus Weak humusmineral mixture Dry, brown to reddish-brown with variable accumulations of clay, calcium carbonate, and soluble salts Desert Soil (hot, dry climate) Clay, calcium compounds Grassland Soil (semiarid climate) Fig. 10.15a, p. 223 Soil erosion Causes – mainly water and wind Human induced causes – farming, logging, mining, construction, overgrazing by livestock, off-road vehicles, burning, and more (go us!) Soil erosion Types Sheet Uniform loss of soil, usually when water crosses a flat field Rill Fast flowing water cuts small rivulets in soil Gully Rivulets join to become larger, channel becomes wider and deeper, usually on steeper slopes or where water moves fast Global soil loss This is a major problem world wide Have lost about 15% of land for agriculture to soil erosion Overgrazing Deforestation Unsustainable farming Also 40% of ag land is seriously degraded due to soil erosion, salinization, water logging and compaction Moderate Severe Desertification of arid and semiarid lands Very Severe Fig. 10.21, p. 228 Areas of serious concern Areas of some concern Stable or nonvegetative areas Global soil erosion Fig. 10.19, p. 226 Desertification Turning productive (fertile) soil into less productive soil (10% loss or more) Overgrazing Deforestation Surface mining Poor irrigation techniques Poor farming techniques Soil compaction Salinization As water flows over the land, salts are leached out When water irrigates a field it is left to evaporate typically This repeated process causes the dissolved salts to accumulate and possibly severely reduce plant productivity Fields must be repeatedly flushed with fresh water to remove salt build up Waterlogging When fields are irrigated they allow water to sink into the soil. Winds can dry the surface As more water is applied the root area of plants is over saturated reducing yield As clay is brought to subsoil levels it can act as a boundary for water infiltration Evaporation Transpiration Evaporation Evaporation Waterlogging Less permeable clay layer Fig. 10.22, p. 229 Soil conservation Conservation tillage – (no till farming) disturb the soil as little as possible Reducing erosion also helps – save fuel, cut costs, hold water, avoid compaction, allow more crops to be grown, increase yields, reduce release of carbon dioxide Soil conservation Terracing – making flat growing areas on hillsides Contour farming – planting crops perpendicular to the hill slope, not parallel Strip cropping – planting alternating rows of crops to replace lost soil nutrients (legumes) Alley cropping – planting crops between rows of trees Control planting and strip cropping Fig. 10.24b, p. 230 Alley cropping Fig. 10.24c, p. 230 Fig. 10.24a, p. 230 Terracing Soil conservation Gully reclamation – seeding with fast growing native grasses, slows erosion or “reverses” it Also building small dams traps sediments Building channels to divert water or slow water Windbreaks – trees planted around open land to prevent erosion Retains soil moisture (shade, less wind) Habitats for birds, bees, etc. Land classification – identify marginal land that should not be farmed Windbreaks Fig. 10.24d, p. 230 Soil fertility Inorganic fertilizers – easily transported, stored, and applied Do not add humus – less water and air holding ability, leads to compaction Only supply about 3 of 20 needed nutrients Requires large amount of energy for production Releases nitrous oxide (N2O) during production, a green house gas Soil fertility Organic fertilizers – the odor is a problem Animal manure – difficult to collect and transfer easily, hard to store Green manure – compost, aerates soil, improves water retention, recycles nutrients Crop rotation – allows nutrients to return to soil, otherwise same crop continually strips same nutrient, keeps yields high, reduces erosion See you on the farm! Remember without farming we all starve But unless we change our farming practice we continue to damage our environment
