Earth Structure

1. Earth Structure

3. Earth Structure CONTINENTAL CRUST OCEANIC CRUST Continental crust -“Granitic” Oceanic crust - “Basaltic” CRUST CRUST Mohorovivic Discontinuity (Moho) Peridotite (olivine & augite) MANTLE MANTLE Gutenberg Discontinuity Iron & Nickel CORE CORE This is a compositional layering of the Earth i.e. by what material the layers are made of.

4. Earth Structure solid (cool, brittle & rocky) CRUST LITHOSPHERE partially molten (only 1-5% molten) ASTHENOSPHERE MANTLE solid (solid-state convection) MESOSPHERE liquid OUTER CORE CORE INNER CORE solid This is a mechanical layering of the Earth i.e. by what properties the layers have.

5. Earth Structure Crust Mantle Core Compositional

6. Earth Structure Seismic wave velocities 6km/s Continental crust Crust Lithosphere Oceanic crust 7km/s Upper mantle 8km/s 7.8km/s Asthenosphere Upper mantle Mantle Mesosphere 13km/s Mantle Outer Core 8km/s Outer core Core Inner Core 11km/s Inner core Compositional Mechanical

7. Continental crust Granitic >65% 2.7 Lithosphere (solid/brittle) Oceanic crust 3.0 Basaltic 45-52% 150km 3.3 (weak / ductile) Asthenosphere 250km Mesosphere Peridotite <45% Mantle (solid) 5.5 [solid-state convection due to high pressures & temperatures over long periods of time] 8.0 2,900km Metallic Outer core 0% 10 (liquid) (Fe , Ni , S) Core 5,100km Inner core Metallic 0% 14 (solid) (Fe & Ni) 6,300km

8. Mid-oceanic ridge Continental crust Granitic Lithosphere Oceanic crust Basaltic MOHO Peridotite Upper mantle Asthenosphere

9. Temperature Variation within Earth’s Interior 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.

10. Temperature Variation within Earth’s Interior Temperature (°C) Asthenosphere (semi-solid) Mesosphere (solid) Depth (km) Outer Core (liquid) Inner Core (solid)

11. 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

12. <4000 million years <200 million years Age 35km (rift valleys) – 70km (mountains) Thickness 6-10km 3.0g/cm3 2.6 – 2.7g/cm3 Density Composition Basaltic Granitic Upper crust, lower crust Sediments, Pillow lavas, Sheeted dykes, Gabbro Structure Subduction Continental collision Formation Sea-floor spreading

13. Evidence for Earth Structure • Seismic Waves • Density of Earth • Earth’s Magnetic Field • Meteorites

14. Seismic Waves i). L-Waves (long waves) 1. Surface Waves 2. Body 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)

15. Seismic Waves Velocity 3 2 4 Inner Core Mesosphere Outer Core 5 1 Asthenosphere 7 Lithosphere 6

17. Mid-oceanic ridge Continental crust Granitic Lithosphere Oceanic crust Basaltic MOHO Peridotite Upper mantle Asthenosphere

18. Continental crust 6 Granitic >65% 2.7 Lithosphere (solid/brittle) Oceanic crust 7 3.0 Basaltic 45-52% 8 150km 3.3 (weak / ductile) 7.8 Asthenosphere 250km Mesosphere Peridotite <45% Mantle (solid) 5.5 [solid-state convection due to high pressures & temperatures over long periods of time] 13 8.0 2,900km Metallic Outer core 0% 8 10 (liquid) (Fe , Ni , S) Core 5,100km Inner core Metallic 11 0% 14 (solid) (Fe & Ni) 6,300km

19. 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

23. 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?

24. 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.

26. Meteorites

27. Meteorites Stony Meteorites

28. Iron Meteorites

32. Density

34. Earth’s Magnetic Field