Download What are plate tectonics and what causes it?

What are plate tectonics and
what causes it?
By: Mr. D’Angelone
Learning Objectives
• Students will name some crustal plates.
• Students will describe the theory of plate
tectonics.
• Students will describe the causes of plate
tectonics.
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Key Terms
•
•
•
•
tectonic plate
theory of plate tectonics
convection current
boundary
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Tectonic Plates
• Earth's lithosphere is made up of crust and
the solid, uppermost part of the mantle.
• The mantle is the layer of rock below the
crust.
• The lithosphere is broken up into large
pieces called tectonic plates.
• There are 7 large tectonic plates and
about 14 smaller ones.
• The largest plate is the Pacific plate.
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Tectonic Plates
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Floating Plates
• Part of the mantle contains rock that flows
like a thick liquid.
• This part, called the athenosphere, is just
below the more solid rock of the
uppermost mantle.
• Tectonic plates float on the athenosphere
like rafts floating on a lake.
• The continents and oceans are carried
along on the plates like passengers on a
raft.
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Theory of Plate Tectonics
• Using information that supports seafloor
spreading and continental drift, scientists have
developed the theory of plate tectonics.
• The theory of plate tectonics combines the
theories of continental drift and seafloor
spreading.
• The theory of plate tectonics explains how and
why the continents move.
• It states that Earth's lithosphere is broken into
plates that float on the upper mantle. The
continents move because they are carried along
on the moving plates.
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What causes plate tectonics?
Convection Currents
• A convection current is the movement of a
gas or a liquid caused by differences in
temperature and density.
• For example, warm air rises and cool air
sinks. When a pan of water boils on a
stove, the water near the bottom of the
pan heats first. The less dense hot water
rises. The cooler and denser water near
the top of the pan sinks.
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Convection Currents
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Inside the Mantle
• Scientists think that giant convection currents in
Earth's upper mantle cause the tectonic plates to
move.
• The mantle rock close to Earth's core is hot and
has some properties of a thick liquid.
• The mantle rock farther from the core is cooler.
• The hot mantle rock rises. The cooler mantle
rock sinks.
• As the cooler rock moves closer to the core, it
heats up and rises.
• The plates are carried along like packages on a
moving conveyor belt or like people on a raft.
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Plate Boundaries and Movements
• The place where two plates meet is called
a plate boundary.
• Scientists have identified three different
kinds of plate boundaries: transform,
convergent, and divergent.
• At transform boundaries, two plates slide
past each other.
• The movement is not smooth. This sliding
movement causes earthquakes.
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• At a convergent boundary, the plates
move toward each other.
• When oceanic crust meets continental
crust, the denser oceanic crust slides
under the continental crust.
• This downward movement of the oceanic
crust produces a subduction zone
• If two continental plates meet, the crust
crumples upward.
• At a divergent boundary, the plates move
apart. These plates sometimes form rift
valley.
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• When oceanic crust meets continental crust at a
convergent boundary, a subduction zone forms.
This is often an area of volcanic activity.
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Mountain Range
• When two continental crusts meet at a
convergent boundary, they crumple upward.
Mountains may be formed.
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Rift Valley
• A rift valley may form at a divergent boundary.
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Checking Concepts
1. Which layer of Earth is below the crust?
2. How many large tectonic plates are
there?
3. What land feature may be formed when
two continental plates meet?
4. At which type of boundary do plates
move apart?
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Answers
1.
2.
3.
4.
Mantle
Seven
A mountain
Divergent
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The End