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Chapter 3 Plate Tectonics

Chapter 3 Plate Tectonics. 3.1 Interior of Earth. Investigating Earth’s structure Shape, size, mass, magnetic field Arrival times of seismic waves Generated by earthquakes, volcanic eruption, humanmade explosions

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Chapter 3 Plate Tectonics

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  1. Chapter 3 Plate Tectonics

  2. 3.1 Interior of Earth • Investigating Earth’s structure • Shape, size, mass, magnetic field • Arrival times of seismic waves • Generated by earthquakes, volcanic eruption, humanmade explosions • Speed depends on chemistry, density and physical state (solid, partially molten, molten) • Types of waves • Shadow zones

  3. 3.1 Interior of Earth, continued • Internal layers • Inner core • Outer core • Mantle • Seismic tomography  three-dimensional image • Crust • Mohorovičić discontinuity, or Moho

  4. 3.2 Lithosphere and Asthenosphere • The layers • Lithosphere • Crust and upper material fused together • Asthenosphere • Deformable region in the mantle • Mesosphere • Solid lower mantle • Isostasy • Buoyant support of lithosphere by asthenosphere

  5. 3.3 Movement of Continents • History of a theory: continental drift • Evidence for a supercontinent (Pangaea) • Subsidence theory of separation • Continental drift • Evidence for a new theory: seafloor spreading • Sea floor survey • Mid-ocean ridge and rise systems • Rift valley • Trenches • Whole-mantle convection

  6. 3.3 Movement of Continents, continued • Evidence for crustal motion • Distribution of earthquake epicenters, heat flow, sediment age, and thickness • Radiometric age of land and sea floor rocks • Paleomagnetism • Polar wandering curves • Record of tectonic plate position relative to magnetic pole

  7. 3.4 Plate Tectonics • Plates and their boundaries • Moving plates and earthquake belts • Divergent boundaries • Mantle upwelling • Layers of oceanic crust • Transform boundaries • Usually offset segments of ocean ridges (two divergent boundaries) • Can also joint up different combination of divergent and convergent boundaries • Changes in speed and direction of moving plates

  8. 3.4 Plate Tectonics, continued • Convergent boundaries • Subduction • Thickness and age of oceanic crust • Volcanic activity associated with ocean-continent convergent boundaries • Continent-continent convergent boundaries • Continental margins • Passive, or trailing, margins • Active, or leading, margins

  9. 3.5 Motion of the Plates • Mechanisms of motion • Not fully understood • Theory of slab pull • Thick, dense crust sinks and drags the remainder of the plate with it • Rates of motion • Spreading rate • Differences between ridges with slow and fast spreading rates • Hot Spots • Hawaiian Islands system

  10. 3.6 History of the Continents • The breakup of Pangaea • History of plate movements for past 225 million years • Before Pangaea • Analysis of continental crust (ocean crust too young) • Six major continents • History of movements from 555 million years ago to 225 million years ago • Terranes • Cratons: large pieces of granitic crust that collided to form North America • Terranes: smaller crustal fragments associated with craton margins

  11. Field Notes: Exploring the Oceans on Earth and Elsewhere • Technological advances for remote exploration • Robotics, communications, distributed power, computing, sensor development, and information management • NEPTUNE observatory planned for Juan de Fuca Plate • Cable network to observe chemical, physical, and biological processes acting within the ocean and crust • Tools developed for remote exploration of Earth will facilitate extraterrestrial exploration • Similarities between Europa and Earth

  12. 3.7 Research Projects and Plans • Project FAMOUS • Visual study of a rift valley using submersibles • Seafloor spreading and hydrothermal vents • Circulation of seawater through newly formed crust • “Lost City” hydrothermal vent system • Major active research programs

  13. 3.7 Research Projects and Plans, continued • Hydrothermal vent communities • Discovery of large communities of animals far from surface food sources • Bacteria rely on hydrogen sulfide and particulate sulfur for their food; no food is needed from the surface • The ocean drilling program • Goal is to answer questions about: • Global climate change and sea level fluctuations • Creation and destruction of ocean basins, volcanoes, and earthquakes • Evolution of life forms

  14. Boxed Reading: Recovery of Black Smokers • Endeavour segment of the Juan de Fuca Ridge • Most active hydrothermal vent region discovered • Preliminary surveys using ROV Jason and the submersible Alvin • Remotely Operated Platform for Ocean Science (ROPOS) • A cage, a chain saw with carbide and diamond-embedded blocks, and a basket, plus a camera and a fiberoptic tether • Four smokers were recovered for geological, chemical, and biological analysis

  15. Summary • Earth is formed of concentric layers: crust, mantle, liquid outer core, and solid inner core • Density of continental crust versus oceanic crust • Isostasy • Wegener’s theory of continental drift • Sea floor spreading • Old lithospheric material sinks at subduction zones • New lithospheric material is formed at the ridges or spreading centers • Evidence for lithospheric motion • Hydrothermal vents • Methods for exploring and monitoring the formation of oceanic crust

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