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Earth Science. Coach Williams Room 310B. Chapter 17. Plate Tectonics. Section 17.1: Drifting Continents. Objectives Describe one piece of early evidence that led people to suggest the Earth’s continents my have once been joined. Discuss evidence of continental drift

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earth science

Earth Science

Coach Williams

Room 310B

chapter 17
Chapter 17
  • Plate Tectonics
section 17 1 drifting continents
Section 17.1: Drifting Continents


  • Describe one piece of early evidence that led people to suggest the Earth’s continents my have once been joined.
  • Discuss evidence of continental drift
  • Explain why continental drift was not accepted when it was first proposed.
early observations
Early Observations
  • Fit of continents across Atlantic Ocean
  • Gondwanaland: southern continents
continental drift
Continental Drift
  • Theory that Earth’s continents were once joined.
  • Continents had slowly drifted apart
  • Pangaea: “all the Earth”
continental drift evidence
Continental Drift Evidence
  • Rocks: similar rocks
  • Fossils: animal/plant remains
  • Ancient Climate: coal in Antarctica
rejected hypothesis
Rejected Hypothesis
  • 2 Reasons the theory was rejected
    • 1) What forces could cause them to move?
    • 2) How could continents move and not shatter?
section 17 2 seafloor spreading
Section 17.2: Seafloor Spreading


  • Summarize the evidence that led to the discovery of seafloor spreading.
  • Explain the significance of magnetic patterns on the seafloor.
  • Explain the process of seafloor spreading.
help from technology
Help From Technology
  • Sonar- sound waves to determine depth
  • Magnetometer- detects changes in magnetic fields
  • Map the ocean floor
ocean floor topography
Ocean Floor Topography
  • Mountain ranges (ridges), trenches
  • Earthquakes & volcanoes
ocean rocks and sediments
Ocean Rocks and Sediments
  • Varying ages of rocks: pattern
    • Younger rocks near ridges
    • Older rocks farther away
  • Sediments
    • Thinner than continental crust
    • Thickness increased farther away from ridge
  • Paleomagnetism: study of magnetic record
    • Basalt(Iron) = compass needle
  • Magnetic reversal: change in Earth’s magnetic field
  • Magnetic symmetry: matching strips on each side of ridge
seafloor spreading
Seafloor Spreading
  • New crust created at ridges
  • Crust is destroyed at trenches
  • Magma comes out of ridges
  • New rock pushes crust outward
  • Provided evidence for continental drift
section 17 3 theory of plate tectonics
Section 17.3: Theory of Plate Tectonics


  • Explain the theory of plate tectonics
  • Compare/contrast the three types of plate boundaries and the features associated with each.
theory of plate tectonics
Theory of Plate Tectonics
  • Earth’s crust: large slabs called plates
  • Major and smaller plates
plate boundaries
Plate Boundaries
  • Plate boundaries: where plates meet
    • Divergent
    • Convergent
    • Transform
divergent plate boundaries
Divergent Plate Boundaries
  • Plates moving apart
  • Most on ocean ridges
  • Rift valley: narrow valley along divergent boundary
convergent plate boundaries
Convergent Plate Boundaries
  • Plates moving together
    • Oceanic crust – oceanic crust: volcanoes
    • Oceanic crust – continental crust: volcanoes
    • Continental crust – continental crust: mountains
  • Subduction- one plate goes below the other
transform plate boundaries
Transform Plate Boundaries
  • Plates slide horizontally
section 17 4 cause of plate motions
Section 17.4: Cause of Plate Motions


  • Explain the process of convection
  • Summarize how convection in the mantle is related to the movements of tectonic plates
  • Compare/contrast the processes of ridge push and slab pull
mantle convection
Mantle Convection
  • Convection: movement due to temperature differences
  • Mantle has convection currents
  • Currents move plates
  • Ridge push- weight of ridge pushes plate down
  • Slab pull- weight of plate pulls plate down