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6.2 The Theory of Plate
Tectonics
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How is water in a pot that is held over
a flame become heated throughout,
even though the flame touches only the
bottom of the pot?
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Plate tectonics
•The theory that Earth’s lithosphere is
divided into tectonic plates that move
around on top of the asthenosphere.
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Tectonic plates
•Pieces of the lithosphere that move around on the top
of the asthenosphere
•Tectonic plates float on the asthenosphere like ice
cubes float in juice.
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Tectonic Plate Boundaries
•A boundary is a place where tectonic
plates meet.
•Locations of earthquakes, volcanoes,
and landforms.
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Why do tectonic plates made of continental
lithosphere displace more asthenosphere than
tectonic plates made of oceanic lithosphere do ?
Continental lithosphere has a greater thickness and
displaces more asthenosphere than thin oceanic
lithosphere does.
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Plate Tectonics
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Convergent Boundaries
•The boundary where two tectonic plates collide.
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Three Types
•Two continental plates collide which forms a mountain
range.
•An oceanic plate collides with a continental plate which
causes the more dense oceanic plate to sink
(subduction). Subduction can cause a chain of
volcanoes to form parallel to the plate boundary.
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•Two oceanic plates collide. The denser plate
subducts which causes series of volcanic islands,
called an island arc.
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Divergent Boundaries
•The boundary where two tectonics plates
separate.
•Some boundaries happen on land (Iceland
and eastern Africa)
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Divergent Boundaries


Some boundaries
happen on the sea
floor.
As the plates pull apart
fractures form on the
ocean floor. Magma
solidifies to form new
lithosphere.
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Transform Boundaries
•The boundary at
which two tectonic
plates slide past one
another horizontally.
•Occurs mostly in the
sea floor at the midocean ridge.
•Another example is
San Andreas fault.
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Compare the three types of plate boundaries.
At convergent boundaries, tectonic plates are
colliding. When these collisions occur, mountain
ranges or a chain of volcanoes or volcanic
islands may form. At divergent boundaries, a
series of fractures forms in the lithosphere as
plates separate. Magma rises through these
fractures to form new lithosphere. At transform
boundaries, two tectonic plates slide past each
other horizontally.
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Tectonic Plate Motion
•Plate movement happens because of the
difference in density caused by the flow of
heat within the Earth.
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•Convection occurs in the Earth’s core and
mantle moving the heat.
•Convection currents is the process where hot,
less dense rock rises and at the surface cold,
dense rock subducts.
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Plate Tectonics
List 5 facts about the video you watch.
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tectonics\How_the_Inner_Structure_of_Plane
t_Earth_Affects_Plate_Tectonics.asf
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Review Questions
1.
What is the theory of plate tectonics?
The theory of plate tectonics is the theory
that explains how tectonic plates move and
change shape.
2.Describe the three types of plate boundaries.
At convergent plate boundaries, tectonic
plates collide. At divergent boundaries,
tectonic plates separate. At transform
boundaries, two plates slide past each other
horizontally.
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3.How does the motion of tectonic plates relate to
continental drift?
The continents are carried along as passengers on
the moving tectonic plates.
4. How do mountain building and volcanoes relate to
plate motion at convergent boundaries?
Volcanoes form at convergent and divergent plate
boundaries. Mountains form where two plates of
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continental lithosphere collide.
Quiz 6.2 Review
• convergent boundaries
•Divergent boundaries
•Transform boundaries
•Convection in mantle
•Plate tectonics
•Tectonic plates
•Boundary
•Flow of heat (warmer to cooler)
•Sea-floor spreading
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