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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 floor topography1

Ocean Floor Topography

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

Seafloor spreading1

Seafloor Spreading

Seafloor spreading2

Seafloor Spreading

Seafloor spreading3

Seafloor Spreading

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

Earth s plates

Earth’s Plates

Plate boundaries

Plate Boundaries

  • Plate boundaries: where plates meet

    • Divergent

    • Convergent

    • Transform

Plate boundaries1

Plate Boundaries

Plate boundaries2

Plate Boundaries

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

Convergent plate boundary

Convergent Plate Boundary

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

Push and pull

Push and Pull

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