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Earth Structure
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Earth Structure CONTINENTAL CRUST OCEANIC CRUST Continental crust -“Granitic” Oceanic crust - “Basaltic” CRUST CRUST Mohorovivic Discontinuity (Moho) Peridotite (olivine & augite) MANTLE MANTLE Gutenberg Discontinuity CORE Iron & Nickel CORE This is a compositional layering of the Earth i.e. by what material the layers are made of.
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Earth Structure CRUST solid (cool, brittle & rocky) LITHOSPHERE partially molten (only 1-5% molten) ASTHENOSPHERE MANTLE MESOSPHERE solid (solid-state convection) liquid OUTER CORE CORE INNER CORE solid This is a mechanical layering of the Earth i.e. by what properties the layers have.
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Earth Structure Crust Mantle Core Compositional
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Compositional Mechanical Earth Structure Crust Lithosphere Mantle
Seismic wave velocities 6km/s Continental crust Crust Lithosphere Oceanic crust 7km/s 8km/s Upper mantle Asthenosphere 7.8km/s Upper mantle Mantle Mesosphere 13km/s Mantle Outer Core 8km/s Outer core Core Inner Core 11km/s Inner core Compositional Mechanical
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Continental crust 2.7 Granitic >65% Lithosphere Oceanic crust (solid/brittle) 3.0 Basaltic 45-52% 150km 3.3 (weak / ductile) Asthenosphere 250km Mesosphere Peridotite Mantle <45% (solid) 5.5 [solid-state convection due to high pressures & temperatures over long periods of time] 8.0 2,900km Metallic Outer core 10 0% (liquid) (Fe , Ni , S) Core 5,100km Inner core Metallic 14 0% (solid) (Fe & Ni) 6,300km
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Mid-oceanic ridge Continental crust Lithosphere Oceanic crust
Granitic Lithosphere Oceanic crust Basaltic MOHO Peridotite Upper mantle Asthenosphere
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Melting point of Peridotite (°C)
Temperature Variation within Earth’s Interior Depth (km) Geotherm (°C) Melting point of Peridotite (°C) 15 1200 50 1250 1350 200 1450 1600 500 1900 2100 1000 2500 3000 2000 3250 3600 4000 3850 4250 4050 5000 4200 6000 4500 Plot the data onto graph paper, with depth on the vertical axis. Describe how the geotherm varies with depth. Define the geotherm. Locate the Earth’s internal layers on the graph. Describe the physical state of the Earth’s interior in relation to the melting point curve. Calculate the average geothermal gradient for the first 50km into the Earth.
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Asthenosphere (semi-solid)
Temperature Variation within Earth’s Interior Temperature (°C) Asthenosphere (semi-solid) Mesosphere (solid) Depth (km) Outer Core (liquid) Inner Core (solid)
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Asthenosphere (semi-solid) Where does this heat come from?
Temperature Variation within Earth’s Interior Temperature (°C) Lithosphere (solid) Asthenosphere (semi-solid) Melting curve Geotherm Mesosphere (solid) Depth (km) Where does this heat come from? Outer Core (liquid) Radiogenic heat Inner Core (solid) Primordial heat
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Oceanic Continental Age Thickness Density Composition Structure
<4000 million years Age <200 million years 35km (rift valleys) – 70km (mountains) Thickness 6-10km Density 3.0g/cm3 2.6 – 2.7g/cm3 Composition Basaltic Granitic Structure Sediments, Pillow lavas, Sheeted dykes, Gabbro Upper crust, lower crust Subduction Continental collision Formation Sea-floor spreading
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Evidence for Earth Structure
Seismic Waves Density of Earth Earth’s Magnetic Field Meteorites
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Seismic Waves 1. Surface Waves 2. Body Waves i). L-Waves (long waves)
i). P-Waves (push waves) travel through liquids & solids fastest waves (4 – 7km/s) both travel faster as material gets more rigid & less compressible ii). S-waves (shake waves) travel through solids only slower than P-waves (2 - 5km/s)
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Seismic Waves Velocity
3 2 4 Inner Core Mesosphere Outer Core 5 1 Asthenosphere 7 Lithosphere 6
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Mid-oceanic ridge Continental crust Lithosphere Oceanic crust
Granitic Lithosphere Oceanic crust Basaltic MOHO Peridotite Upper mantle Asthenosphere
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Continental crust 6 2.7 Granitic >65% Lithosphere Oceanic crust (solid/brittle) 7 3.0 Basaltic 45-52% 150km 8 3.3 (weak / ductile) Asthenosphere 7.8 250km Mesosphere Peridotite Mantle <45% (solid) 5.5 [solid-state convection due to high pressures & temperatures over long periods of time] 13 8.0 2,900km Metallic Outer core 8 10 0% (liquid) (Fe , Ni , S) Core 5,100km Inner core Metallic 11 14 0% (solid) (Fe & Ni) 6,300km
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Seismic Waves Refraction
Seismograph Station 2 Direct Reflected Refracted Seismograph Station Epicentre Focus Layer 1 (Crust) Boundary between layer 1 & 2 (Moho) Layer 2 (Mantle) h = depth Хd = distance from epicentre where all seismic waves arrive at same time V1 = velocity of P waves in layer 1 V2 = velocity of P waves in layer 2
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Suppose the shadow zone for P waves was located between 120 and 160º rather than 103 and 142º. What would this indicate about the size of the core?
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Why is there a S-wave shadow zone?
There is a S-wave shadow zone from where the S-waves cannot reach the other side of the Earth as they are stopped by the liquid outer core. Liquids cannot transmit shear waves due to the weak bonding between particles.
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Meteorites
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Meteorites Stony Meteorites
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Iron Meteorites
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Density
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Earth’s Magnetic Field
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