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Plate tectonics
 

Plate tectonics

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    Plate tectonics Plate tectonics Presentation Transcript

    • Plate Tectonics Continental Drift
    • 4-1 Continental Drift – objectives…
      • Explain Wegener’s hypothesis of continental drift.
      • List evidence for Wegener’s hypothesis of continental drift.
      • Describe seafloor spreading.
    • Continental Drift
      • Began with observations made over 400 years ago.
      • The first reliable maps were studied and it was noticed that the continents fit together like a puzzle.
    • Hypothesis on Continental Drift.
      • The continents were once part of the same landmass – Pangea
      • Surrounding Pangea was a great ocean – Panthalassa
      • About 200 mya, Pangea began breaking apart.
      • This motion caused crumpling which led to today’s land features.
    • Alfred Wegener
      • A german scientist.
      • Proposed his hypothesis on continental drift in 1912.
    • Observations led to questions…
      • Were the continents once part of the same landmass?
      • If so, what caused this landmass to break apart?
      • What caused the continents to move to their present locations?
    •  
    •  
    • Evidence
      • Coastline similarities
    • Evidence
      • Fossils
        • Mesosaurus
        • Cynognatyhus
        • Lystrosaurus
        • Glossopteris
    •  
    • Geologic Evidence
      • Age and types of rocks
      • Mountains
        • Applachian mountains fit continuously with a band of mountains in Greenland.
    • Climatic Evidence
      • Layers of glaciers in southern Africa and South America
      • Coal deposits in the Eastern US, Europe, and Sibera
      • These climatic similarities are easy to explain if the continents were once joined.
    • Climatic Evidence - glaciation
      • Evidence of ancient glaciation indicated that parts of southern Africa, India, Australia, and South America were covered by a large ice sheet. Arrows indicate direction of ice movement.
    • There was little support for Wegner’s hypothesis….until.two decades after his death…
    • Seafloor Spreading
      • 1947, mapping the Mid-Atlantic Ridge
        • Discovered the ocean floor is much younger than continental rocks.
          • Oceanic rocks – 150 million years old
          • Continental rocks – 4 billion years old
      • Harry Hess suggested a hypothesis
        • Seafloor spreading
          • Rocks in/near the rift were younger as a result of the upwelling and solidification of magma.
    • Seafloor Spreading
      • Seafloor spreading provided the support Wegner needed for a mechanism for continental drift.
      • Still no proof…
    • Paleomagnetism
      • Magnetism resulting from the cooling of magma mirrors the existing magnetism of the earth.
      • Magnetic orientations were discovered that appeared normal then reversed…normal then reversed…
      • This supported seafloor spreading…and thus further anchored Wegner’s Hypothesis.
    • Paleomagnetism
    • Review of 4-1…
      • What observation first led to Wegner’s hypothesis of continental drift?
      • What types of evidence support Wegener’s hypothesis?
      • Describe the process of seafloor spreading.
      • Explain how scientists know that the earth’s magnetic poles have reversed themselves many times during earth’s history.
    • 4-2 – Plate Tectonics - objectives
      • Summarize the theory of Plate Tectonics.
      • Compare the characteristic geologic activities that occur along the three types of plate boundaries.
      • Explain the possible role convection currents in plate movement.
      • Summarize the theory of suspect terranes.
    • A theory emerges…
      • 1960’s…
      • A combination of continental drift and seafloor spreading…
      • Describes continental movement but also proposes a possible explanation of why and how continents move.
    • The Earth’s Layers
      • Two types of crust:
        • Oceanic – ocean floor
        • Continental – dry land
      • Both types of crust plus the rigid upper mantle make up the Lithosphere.
      Himilayian Crust
    • The Earth’s Layers
      • Lithosphere – the thin outer layer
        • Lithospheric plates
      • Asthenosphere – a layer of “plastic” rock
        • Denser than the lithosphere.
    • Earth’s Layers
    • Lithospheric Plate Boundaries
    • Lithospheric Plate Boundaries
      • Continent margins don’t necessarily follow plate boundaries.
      • 30 plates have been identified at some speed of constant motion.
    • Types of Plate Boundaries
    • Divergent Boundaries
      • spreading centers where two lithospheric plates move away from each other
    • Divergent Boundaries
    • Convergent Boundaries
      • A converging boundary forms when two plates move toward each other
      • Two Types
        • Collision
        • Subduction
    • Convergent Boundary - Collision
      • Oceanic crust – Oceanic crust
    • Convergent Boundary - Collision
      • Oceanic crust – continental crust
    • Convergent Boundaries
      • Continental crust – continental crust
    •  
    •  
    • Transform Fault Boundaries
      • San Andreas fault, California
    • Causes of Plate Motion
      • Many scientists think that the movement of the lithospheric plates is due to convection currents.
    • Convection Currents