Plate Tectonics by ewghwehws

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									             Plate Tectonics

                  Chapter 17
                     Great Idea:
 The entire earth is still changing, due to the slow
convection of soft, hot rocks deep within the planet.
          Chapter Outline
• The Dynamic Earth
• Plate Tectonics: A Unifying View of
  Earth
• Another Look at Volcanoes and
  Earthquakes
The Dynamic Earth
         The Dynamic Earth
• Small-scale changes
  – Construction site
    • Erosion by rain
• Large-scale changes
  – Volcanoes
  – Earthquakes
  – Erosion
           The Case of the
       Disappearing Mountains
• Erosion
  – Few hundred million years
  – Mountains continually forming
• Earth’s surface is not static
    Volcanoes and Earthquakes-
   Evidence of Earth’s Inner Forces
• Volcano
  – Magma breaks
    through surface
• Earthquake
  – Rocks breaks
    along fault
  – Energy
    transmitted as
    wave
  – Richter scale
  The Movement of the Continents

• F. Bacon
  – Continents like a
    puzzle
• Wegener
  – Continental Drift
     • Continents in
       motion
• Current Evidence
  – Ocean Floors
  – Magnetic Reversals
  – Rock Ages
            Ocean Floors
• Mapping
 – Ocean floor dynamic
   • Canyons, mountains
   • Mid-Atlantic Ridge
     – Earthquakes,
       volcanoes,
       lava flows
          Magnetic Reversals
• Earth’s magnetic field
  – Changes periodically
• Magnetite
  – Crystals in lava align to magnetic field
• Paleomagnetism
• Seafloor Spreading
  – New rock comes to surface
Magnetic Reversals
              Rock Ages
• Radioactive Isotopes
  – Rocks near Mid-Atlantic Ridge younger
  – Rocks farther away older
   New Support for the Theory
• Measuring motion of continents
• Radio Astronomy
  – Measured arrival of radio waves
  – Repeated over several years
• North America and Europe
  – Separating at 5 cm per year
Plate Tectonics: A Unifying
       View of Earth
               Plate Tectonics
• Plate Tectonics
  – Large-scale surface features
  – Related phenomena
• Tectonic plates
  – Rigid, moving sheet of rock
  – Crust and upper mantle
  – Continental
     • 100 km thick
     • Lower density (granite)
  – Oceanic
     • 8-10 km thick
     • Dense rock (basalt)
• Earth’s surface
  – ¼ continent, ¾ water
Earth’s Plates
       The Convecting Mantle
• Mantle convection
  – Motion driven by Earth’s interior heat energy
• Sources of energy
  – Gravitational potential energy
  – Decay of radioactive elements
• Movement
  – Heat moves to cooler regions
  – Convection cells in mantle
  – Very slow
    • 200 million years for one cycle
         Plate Boundaries
• Three Main Boundary Types
  – Divergent
  – Convergent
  – Transform
        Divergent Boundaries
• Characteristics
  – Volcanoes
     • Chain of mountains
  – Earthquakes
• Seafloor spreading
  – Plates pushed apart
  – Old spreading centers
     • Located in middle of ocean
  – New spreading centers
     • May begin anywhere
      Convergent Plate Boundaries

• Types
  – Oceanic-oceanic
    • Subduction zone
       – Deep oceanic trench
       – Island arc
  – Continental-continental
    • High, jagged mountain
      chain
  – Continental-oceanic
    • Subduction zone
       – Deep oceanic trench
       – Coastal mountain range
   Transform Plate Boundary
• Two plates move past each other
  – NOT smooth
  – Earthquakes as a result of movement
        The Geological History of
             North America
• Northeastern Canada and Greenland
  – Several billion years old
• Western US
  – Terranes
     • Added to continent over time
• Appalachian Mountains
  – Formed 450-300 million years ago
  – Continental-continental convergence zone
• Rocky Mountains
  – 60 million years ago
  – Warping, folding and fracturing of continent
• The Colorado Plateau
  – Gentle uplift
• The Sierra Nevada
  – Molten rock pushed up sediments
       Another Look at Volcanoes
           and Earthquakes
• Plates and
  Volcanism
  – Divergent Plate
    Boundaries
  – Convergent Plate
    Boundaries
     • Subduction zones
  – Hotspots
     • Source stationary,
       plates move
     • Chain of volcanoes
• Earthquakes
  – At plate boundaries
    or elsewhere
    Seismology: Exploring Earth’s
      Interior with Earthquakes
• Seismology
  – Study of sound vibrations within earth
  – Used to determine earth’s inner
    structure
• Seismic waves
  – Compressional or longitudinal
  – Transverse or shear waves
Seismology: Exploring Earth’s
  Interior with Earthquakes

								
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