Coach Williams
Room 310B
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Plate Tectonics
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.
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Fit of continents across Atlantic Ocean
Gondwanaland: southern continents
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Theory that Earth’s continents were once
joined.
Continents had slowly drifted apart
Pangaea: “all the Earth”
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Rocks: similar rocks
Fossils: animal/plant remains
Ancient Climate: coal in Antarctica
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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?
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.
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Sonar- sound waves to determine depth
Magnetometer- detects changes in magnetic
fields
Map the ocean floor
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Mountain ranges (ridges), trenches
Earthquakes & volcanoes
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Varying ages of rocks: pattern
◦ Younger rocks near ridges
◦ Older rocks farther away
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Sediments
◦ Thinner than continental crust
◦ Thickness increased farther away from ridge
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Paleomagnetism: study of magnetic record
◦ Basalt(Iron) = compass needle
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Magnetic reversal: change in Earth’s magnetic
field
Magnetic symmetry: matching strips on each
side of ridge
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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
Objectives:
 Explain the theory of plate tectonics
 Compare/contrast the three types of plate
boundaries and the features associated with
each.
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Earth’s crust: large slabs called plates
Major and smaller plates
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Plate boundaries: where plates meet
◦ Divergent
◦ Convergent
◦ Transform
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Plates moving apart
Most on ocean ridges
Rift valley: narrow valley along divergent
boundary
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Plates moving together
◦ Oceanic crust – oceanic crust: volcanoes
◦ Oceanic crust – continental crust: volcanoes
◦ Continental crust – continental crust: mountains
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Subduction- one plate goes below the other
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Plates slide horizontally
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
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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