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Geology
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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
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35 km (21 mi.) avg., 1,200˚C Crust 100 km (60 mi.) Low-velocity zone
Mantle Lithosphere Solid 10 to 65km 2,900km (1,800 mi.) 3,700˚C 100 km Asthenosphere (depth unknown) Outer core (liquid) 200 km Core 5,200 km (3,100 mi.), 4,300˚C Inner core (solid) Fig. 10.2, p. 212
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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)
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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
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Plate tectonics The lithosphere is broken into many large plates which move due to convection currents within the asthenosphere Remember continental drift (Pangaea)
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INDIAN-AUSTRLIAN PLATE
Reykjanes Ridge EURASIAN PLATE EURASIAN PLATE Mid- Atlantic Ocean Ridge ANATOLIAN PLATE JUAN DE FUCA PLATE NORTH AMERICAN PLATE CHINA SUBPLATE CARIBBEAN PLATE Transform fault PHILIPINE PLATE ARABIAN PLATE PACIFIC PLATE COCOS PLATE AFRICAN PLATE Mid- Indian Ocean Ridge Transform fault SOUTH AMERICAN PLATE Carlsberg Ridge East Pacific Rise AFRICAN PLATE INDIAN-AUSTRLIAN PLATE Southeast Indian Ocean Ridge Transform fault Southwest Indian Ocean Ridge ANTARCTIC PLATE Plate motion at convergent plate boundaries Divergent ( ) and transform fault ( ) boundaries Plate motion at divergent plate boundaries Convergent plate boundaries Fig. 10.5b, p. 214
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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)
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Trench Volcanic island arc Lithosphere Rising magma Asthenosphere
Subduction zone Trench and volcanic island arc at a convergent plate boundary Fig. 10.6b, p. 215
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Transform fault connecting two divergent plate boundaries
Fracture zone Transform fault Lithosphere Asthenosphere Transform fault connecting two divergent plate boundaries Fig. 10.6c, p. 215
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Oceanic ridge at a divergent plate boundary
Lithosphere Asthenosphere Oceanic ridge at a divergent plate boundary Fig. 10.6a, p. 215
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Mantle (asthenosphere)
Abyssal hills Folded mountain belt Abyssal floor Oceanic ridge Abyssal floor Trench Craton Volcanoes Continental rise Oceanic crust (lithosphere) Continental slope Abyssal plain Continental shelf Abyssal plain Continental crust (lithosphere) Mantle (lithosphere) Mantle (lithosphere) Mantle (asthenosphere) Fig. 10.3, p. 213
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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
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Lake Glacier Tidal Spits flat Shallow marine environment Stream
Barrier islands Dunes Lagoon Delta Dunes Beach Shallow marine environment Volcanic island Coral reef Continental shelf Continental slope Abyssal plain Deep-sea fan Continental rise Fig. 10.7, p. 216
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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
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Types of rock Igneous Sedimentary Metamorphic Granite, pumice, basalt
Shale, sandstone, limestone (coral reef) Metamorphic Slate, marble, quartzite
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Sedimentary Rock Slate, sandstone, limestone Transportation Deposition
Erosion Heat, pressure, stress Weathering EXTERNAL PROCESSES INTERNAL PROCESSES Igneous Rock Granite, pumice, basalt Metamorphic Rock Slate, marble, quartzite Heat, pressure Cooling Magma (molten rock) Melting Fig. 10.8, p. 217
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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
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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
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Soil Produced slowly ( 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
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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.
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Immature soil Young soil Mature soil
Oak tree Lords and ladies Word sorrel Dog violet Earthworm Organic debris Builds up Grasses and small shrubs Millipede Rock fragments Mole Moss and lichen Fern Honey fungus 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 mite Fungus Springtail Mature soil Bacteria Fig , p. 220
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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
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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
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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
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Water Water High permeability Low permeability Sandy soil Clay soil
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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)
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Tropical Rain Forest Soil (humid, tropical climate)
Forest litter leaf mold Acid litter and humus Acidic light- colored humus Humus-mineral mixture Light-colored and acidic Light, grayish- brown, silt loam Iron and aluminum compounds mixed with clay Dark brown Firm clay Humus and iron and aluminum compounds Tropical Rain Forest Soil (humid, tropical climate) Deciduous Forest Soil (humid, mild climate) Coniferous Forest Soil (humid, cold climate) Fig b, p. 223
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Desert Soil (hot, dry climate) Grassland Soil (semiarid climate)
Mosaic of closely packed pebbles, boulders Alkaline, dark, and rich in humus Weak humus- mineral mixture Dry, brown to reddish-brown with variable accumulations of clay, calcium carbonate, and soluble salts Clay, calcium compounds Desert Soil (hot, dry climate) Grassland Soil (semiarid climate) Fig a, p. 223
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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!)
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Soil erosion Types Sheet Rill Gully
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
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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
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Desertification of arid and semiarid lands
Moderate Severe Very Severe Fig , p. 228 Desertification of arid and semiarid lands
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Areas of serious concern Stable or nonvegetative areas
Areas of some concern Stable or nonvegetative areas Global soil erosion Fig , p. 226
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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
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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
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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
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Evaporation Transpiration Evaporation Evaporation Waterlogging
Less permeable clay layer Fig , p. 229
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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
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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
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Control planting and strip cropping
Fig b, p. 230
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Alley cropping Fig c, p. 230
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Fig a, p. 230 Terracing
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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
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Windbreaks Fig d, p. 230
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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
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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
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See you on the farm! Remember without farming we all starve
But unless we change our farming practice we continue to damage our environment
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