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9. Our Living Earth

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  1. 9. Our Living Earth • Earth’s atmosphere, oceans & surface • Earth’s interior & earthquakes • Earth’s plate tectonics activity • Earth’s magnetic field & magnetosphere • Earth’s evolving atmosphere • Earth’s human population & biosphere

  2. The Earth: A Portrait From Space

  3. Earth Data (Table 9-1)

  4. Earth From An Apollo Spacecraft

  5. Earth’s Environmental Spheres • Earth’s spheres • Geosphere Rock & metallic Earth materials • Hydrosphere Water as ice, liquid & humidity • Atmosphere ~78% nitrogen & ~21% oxygen • Biosphere All living things (biomass) • Earth’s ecosystem • Matter flows • A closed system for most practical purposes • Meteoroids enter daily, spacecraft leave occasionally • Energy flows • An open system for most practical purposes • Sunlight brings extremely large amounts of energy on one side • Radiant heat in extremely large amounts leaves onallsides

  6. Rocks • Definition • Consolidated mixture of one or more minerals • Monomineralic rocks have many crystals of 1 mineral • Polymineralic rocks have many crystals of >2 minerals • Making rocks • Igneous processes Fiery origins • Sedimentary processes Cemented small particles • Metamorphic processes Changed by heat/pressure • Destroying rocks • Physical / mechanical weathering • Chemical weathering

  7. Rock Cycle: Materials & Processes • Materials • Magmasolidifies & becomes… • Igneous rockweathers & becomes… • Sedimentlithifies & becomes… • Sedimentary rockmetamorphoses & becomes… • Metamorphic rockmelts & becomes… • Processes • Solidificationproducesigneous rock • Weatheringproducessediment • Lithificationproducessedimentary rock • Metamorphismproducesmetamorphic rock • Meltingproducesmagma

  8. Rock Cycle

  9. Magma: Source of Igneous Rocks • Earth’s interior is hot • Residual heat of formation ~ 4.6 billion years ago • Decay of radioactive isotopes • Earth’s interior is mostly solid or “plastic” • Solid: Rigid / brittle under intense pressure • Plastic: Flows slowly under intense pressure • Localized areas are hot enough to melt rocks • Magma temperatures vary ~ 600°C to ~ 1,400°C • Iron turns red at ~ 600°C& melts at ~ 1,500°C • Magma has ~ 10% greater volume than source • Same mass ⇒ Greater volume ⇒ Lower density

  10. Some Common Igneous Rocks

  11. Sedimentary Rock Categories • Organic Remains of plants & animals • Coal Fossilized fern leaves • Clastic Broken rock & mineral fragments • Sandstone, shale & limestone • Bioclastic Broken shell fragments • Coquina Limestone “fossil hash” • Chemical Crystallization from water solution • Gypsum A common “evaporite” mineral

  12. Some Clastic Sedimentary Rocks

  13. Three Metamorphic Processes • Heat Absolutely essential • Hot enough for atoms & molecules to slowly migrate • Cool enough so that nothing melts • Pressure Common but not essential • Subduction zones Pacific Northwest • Regional subsidence Mississippi Delta • Fluids Only near active volcanoes • Volcanically active areas Eastern Oregon

  14. Foliated Metamorphic Rocks: Gneiss

  15. Oregon’s Metamorphic Environment Portland Astoria

  16. Earth’s “Chemical” Differentiation

  17. Characterizing Earth’s Interior • Chemical composition Mineral composition • Low density minerals Crust • Granite continents & basalt ocean basins • Intermediate density minerals Mantle • Peridotite • High density minerals Core • Iron & nickel • Physical condition Solid / plastic / liquid • A function of temperature & pressure • Temperature increases slowly with depth • Pressure increases rapidly with depth • Solid Lithosphere Old & cool enough • Plastic Asthenosphere Lubricating layer • Solid Mantle Very slightly plastic • Liquid Outer core Temperature wins • Solid Inner core Pressure wins

  18. Earth’s Interior Facts & Evidence • Some basic facts • Overallaverage density ~ 5.5 g . cm–3 • Surface average density ~ 2.7 to 3.0 g . cm–3 • Interior must have higher density materials • Much higher atomic number ⇒ Metals • Greater compression due to greater pressure • Some suggestive evidence • Asteroids orbiting the Sun • Range of materials from rock to iron/nickel • Proportions would produce a planet like Earth • Meteorites found on Earth • Range of materials from rock to iron/nickel • Proportions would produce a planet like Earth

  19. Earth’s Layers: The Lithosphere

  20. Earth’s Layers: Crust/Mantle/Core

  21. The focus is also called the hypocenter Earthquake Focus & Epicenter

  22. Seismic (Earthquake) Waves • Body waves • Source location: Focus • Place of maximum underground shaking • Place where the earthquake begins Usually ! ! ! • Varieties • Compressional waves P-waves Primary waves • Transverse waves S-waves Secondary waves • Surface waves • Source location: Epicenter • Place of maximum surface shaking • Place directly above the focus Usually ! ! ! • Varieties • Compressional waves Sideways jolting • Transverse waves Up & down jiggling

  23. Compressional Seismic Waves Transverse Seismic Waves Compressional & Transverse Waves

  24. Body Seismic Waves

  25. Surface Seismic Waves

  26. Seismicity & Earth’s Internal Structure

  27. Plate Tectonics • Tectonic plates = Lithospheric plates • Rigid & brittle • “Glide” over the asthenosphere • Sizes vary greatly • Micro plates Juan de Fuca plate • Macro plates Pacific plate • Three kinds of tectonic plates • Oceanic plates Basaltic composition • Continental plates Granitic composition • Composite plates Both basalt & granite

  28. Mantle Convection & Plate Motion • Thermal gradient: Hotter at core than at crust • Results in a density gradient • Heat sources • Planetesimal impact Dominant as a protoplanet • Radioactive decay Ongoing exponential decay • Gravitational collapse Minimal as a protoplanet • Point of origin • Thought to be the core-mantle boundary • Shape • Elongated “curtains” of rising material

  29. A Model of Mantle Convection

  30. A Global View of Mantle Convection

  31. Tectonic Plates

  32. Tectonic Plate Boundary Processes

  33. Divergent Plate Boundaries

  34. Convergent Plate Boundaries

  35. Transform Plate Boundaries

  36. Ridge offset by transform faults Mid-Atlantic Ridge Spreading Zone

  37. Effects of Plate Motion: Volcanoes • Divergent tectonic plate boundaries • Most rising magma spreads out under lithosphere • Lithosphere warms ⇒ Lowers density ⇒ Floats higher • Penetrates the lithosphere, causing eruptions • Convergent tectonic plate boundaries • Highest density plate subducts • Ocean ⇒⇐oceancollision • Oldest (i.e., coldest & densest) basaltic plate subducts • Basaltic to andesitic lavas build gently curving line of volcanoes • Ocean ⇒⇐continent collision • Basaltic (therefore most dense) oceanic plate subducts • Andesitic to rhyolitic lavas build gently curving line of volcanoes

  38. Plate Motion Effects: Earthquakes • Divergent tectonic plate boundaries • All activity is near the Earth’s surface • Virtually all earthquakes are shallow • Most rock is relatively warm & soft • Absence of brittle rock reduces earthquake strength • Convergent tectonic plate boundaries • Ocean – ocean boundaries • Deep & strong earthquakes are very common • Ocean – continent boundaries • All depths & strong earthquakes are very common • Transform tectonic plate boundaries • Ocean – ocean boundaries • Absence of brittle rock reduces earthquake strength • Ocean – ocean boundaries • Presence of brittle rock increases earthquake strength

  39. Plate Motion Effects: Mountains • Volcanoes • Usually occur at convergent & divergent boundaries • At least one plate must have basaltic oceanic crust • Factors contributing to solid rock melting • Thermal gradient ⇒ Deeper is hotter • Friction ⇒ Subducting slab ⇔ country rock • Addition of water ⇒ Under-sea subduction trenches • Folded mountains • Occur primarily at convergent boundaries • Both plates must have granitic continental crust • Thrust faulting is also very common • Significant crustal shortening

  40. Plate Motion Effects: Geography • Continent ⇔ ocean configuration very dynamic • Three probable Pangaea episodes • All major landmasses gather into one supercontinent • Remaining 70% of Earth’s surface is one super-ocean • The present situation • Major continental landmasses are relatively stable • Major ocean basins are very dynamic • Atlantic Ocean is increasing in size • PacificOcean is decreasing in size

  41. Earth’s Magnetic Field • Basic physical processes • Slow circulation of the liquid metallic outer core • Rapid axial rotation of once per day • Basic properties • Combined magnetic field of many smaller “cells” • Reverses on average ~ 0.5 million years • May be in the initial stages of a reversal now • Not perfectly aligned with Earth’s rotational axis • True of almost every planet in the Solar System • Magnetic declination • Deviation of magnetic North [compass] away from true North • Magnetic inclination • Angle between Earth’s surface & Earth’s magnetic field lines

  42. Visualizing Earth’s Magnetic Field

  43. Earth’s Magnetosphere • Basic physical processes • Earth’s relatively strong magnetic field • The ever-changing solar wind • Ionized hydrogen atoms Free protons & electrons • This is an electric current Generates a magnetic field • Strong interaction between two magnetic fields • Basic properties • Earth’s magnetosphere shaped like a teardrop • Blunt side faces Sun, pointed side faces opposite Sun • Solar wind gusts produce striking effects • Geomagnetic storms Disrupt radio signals • Occasionally strong enough to disrupt electric power distribution • Aurorae Ionize atmospheric atoms • Occasionally strong enough to be seen in Florida & Texas

  44. Visualizing Earth’s Magnetosphere

  45. Aurora Australis From Space

  46. So-Called “Greenhouse”Effect

  47. Earth’s 3-D Atmospheric Circulation

  48. Earth’s Vertical Atmospheric Structure

  49. Terrestrial Planetary Atmospheres • Venus • ~100 times more atmosphere than Earth • ~ 96.5% CO2 & ~3.5% N2 • Runaway global warming • Very large amount of CO2 & relatively close to the Sun • Earth • ~ 78% N2 & ~21% O2 • Moderate global warming • Very small amount of CO2 & moderately close to the Sun • Mars • ~100 times less atmosphere than Earth • ~ 95.3% CO2 & ~2.7% N2 • Minimal global warming • Very small amount of CO2 & relatively far from the Sun

  50. Source of Planetary Atmospheres • Volcanic outgassing • Venus • Abundant with no oceans to assimilate gases • Earth • Abundant with oceans to assimilate gases • Mars • Absent with no oceans to assimilate gases • Comet impacts • Very common in the young Solar System • Veryrarein today’s Solar System