earth science
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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 - PowerPoint PPT PresentationTRANSCRIPT
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Earth ScienceCoach Williams
Room 310B
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Plate Tectonics
Chapter 17
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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 Explain why continental drift was not
accepted when it was first proposed.
Section 17.1: Drifting Continents
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Fit of continents across Atlantic Ocean Gondwanaland: southern continents
Early Observations
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Gondwanaland
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Theory that Earth’s continents were once joined.
Continents had slowly drifted apart Pangaea: “all the Earth”
Continental Drift
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Rocks: similar rocks Fossils: animal/plant remains Ancient Climate: coal in Antarctica
Continental Drift Evidence
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2 Reasons the theory was rejected◦ 1) What forces could cause them to move?◦ 2) How could continents move and not shatter?
Rejected Hypothesis
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Objectives◦ 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.
Section 17.2: Seafloor Spreading
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Sonar- sound waves to determine depth Magnetometer- detects changes in
magnetic fields Map the ocean floor
Help From Technology
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Mountain ranges (ridges), trenches Earthquakes & volcanoes
Ocean Floor Topography
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Ocean Floor Topography
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Varying ages of rocks: pattern◦ Younger rocks near ridges◦ Older rocks farther away
Sediments◦ Thinner than continental crust◦ Thickness increased farther away from ridge
Ocean Rocks and Sediments
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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
Magnetism
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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 Spreading
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Seafloor Spreading
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Seafloor Spreading
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Seafloor Spreading
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Objectives: Explain the theory of plate tectonics Compare/contrast the three types of plate
boundaries and the features associated with each.
Section 17.3: Theory of Plate Tectonics
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Earth’s crust: large slabs called plates Major and smaller plates
Theory of Plate Tectonics
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Earth’s Plates
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Plate boundaries: where plates meet◦ Divergent◦ Convergent◦ Transform
Plate Boundaries
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Plate Boundaries
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Plate Boundaries
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Plates moving apart Most on ocean ridges Rift valley: narrow valley along divergent
boundary
Divergent Plate Boundaries
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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 Boundaries
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Convergent Plate Boundary
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Plates slide horizontally
Transform Plate Boundaries
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Objectives: 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
Section 17.4: Cause of Plate Motions
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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
Mantle Convection
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Push and Pull