Physics of Plate Movement
SECTION 5.3
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What do we know?
 What are some clues to the movement of the Earth’s
plates?
 What is under the plates?
 What are some forces that act on the Earth’s plates?
Convey the Concept
 Describe how a conveyor belt works.
 Make a list of where conveyor belts are used.
 What happens to objects places on a conveyor belt?
http://thumbs.dreamstime.com/x/cardboard-boxes-conveyor-belt-9299898.jpg
Plate Tectonics
 50 years after Alfred Wegener proposed the theory of
plate tectonics, it was finally accepted.
 Because there has been evidence collected about the
movement of plates, we know:
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How fast plates move
Which direction they move in
And how they interact at boundaries.
 But one question still remains: What is the driving
force that moves the plates?
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Convection in the Mantle
 This question is somewhat answered because we
know that the driving force of the movement has
something to do with the movement of mantle.
 This is where convection occurs.
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Convection- heating of the rock in the partially melted zone of
the mantle causes that material to move in a circular motion.
 Convection occurs in circular units of movement
called convection cells.
 Most scientists agree that convection causes plate
movement but there is no agreement about how
convection happens.
http://www.classroomatsea.net/general_science/images/convection.jpg
Convection in the Mantle
 There are two basic models for convection both
supported by strong evidence.:
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One model shows that convection happens mainly in the
asthenosphere. (Right side of Figure 5.15).
The other model shows that the convection cells are much
larger and they include the entire mantle. (Left side of Figure)
http://web.ics.purdue.edu/~braile/edumod/convect/convect_files/image018.jpg
Models for Plate Movement
 There is disagreement about how convection moves
plates.
 One model shows that the plates are carried along by the
movement of convection. (Passengers on giant conveyor
belts)
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Where convection pushes material upward, divergent boundaries
form.
Where convection goes downward back into the mantle, convergent
boundaries form.
 Another model shows that the plates themselves have an
active role in convection.
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Each plate is thought to be a convection cell.
With the plate being cooler and more dense than the asthenosphere
below, it tends to sink.
This sinking, pulls the rest of the plate down which helps create the
circular movement of convection.
What have we learned?
What are two models for convection in the mantle?
2. If convection cells in the mantle are like conveyer
belts, what are the plates like?
3. Which model do you think best explains how
convection moves the plates? Explain the reasons
for your choice.
4. What are the similarities and differences between
the two major models explaining how convection
causes plate movement?
1.