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Transcript
Coach Williams
Room 310B

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.


Fit of continents across Atlantic Ocean
Gondwanaland: southern continents



Theory that Earth’s continents were once
joined.
Continents had slowly drifted apart
Pangaea: “all the Earth”



Rocks: similar rocks
Fossils: animal/plant remains
Ancient Climate: coal in Antarctica

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.



Sonar- sound waves to determine depth
Magnetometer- detects changes in magnetic
fields
Map the ocean floor


Mountain ranges (ridges), trenches
Earthquakes & volcanoes

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





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.


Earth’s crust: large slabs called plates
Major and smaller plates

Plate boundaries: where plates meet
◦ Divergent
◦ Convergent
◦ Transform



Plates moving apart
Most on ocean ridges
Rift valley: narrow valley along divergent
boundary

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

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





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