Plate Tectonics

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Plate Tectonics
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What are tectonic plates?

• Earths lithosphere is made up of crust the
  solid, uppermost part of the mantle.
• 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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Floating Plates

• The asthenosphere, the part of the mantle that
  flows like a thick liquid, is just below the
  lithosphere.
• Tectonic plates float on the asthenosphere like
  rafts floating on a lake.
• The continents oceans are carried along on the
  plates like passengers on a raft.

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The Theory of Plate Tectonics

• The theory of plate tectonics combines the
  theories of continental drift seafloor
  spreading.
• It explains how why the continents move.
• It states that the Earths 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?

• Scientists believe that giant convection
  currents, movement of a gas or a liquid caused by
  changes in temperature, in Earths upper mantle
  cause the tectonic plates to move.
• Mantle rock close to Earths core is hot, mantle
  rock farther from the core is cooler. The hot
  mantle rock rises, the cooler mantle rock
  sinks. As the cooler mantle rock moves closer to
  the core it heats up rises. This endless cycle
  repeats.
• The plates are carried along like packages on a
  moving conveyor belt.

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Plate Boundaries

• Plate boundaries are places where 2 plates meet.
• There are 3 different kinds of plate boundaries
• Transform
• Convergent
• Divergent

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Transform Boundaries

• Two plates slide past each other horizontally.
• The movement is not smooth.
• This sliding movement causes earthquakes.

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Convergent Boundaries

• Formed by the collision of two plates.
• When oceanic crust meets continental crust, the
  denser oceanic crust slides under the continental
  crust. This produces a subduction zone.
• If two continental plates meet, the crust
  crumbles upward and
  mountains may be
  formed.

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Divergent Boundaries

• The plates are moving away from each other.
• New seafloor forms at divergent boundaries.
• Mid-ocean ridges are the most common type of
  divergent boundary.
• Rift valleys are sometimes formed.

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Effects of Plate Tectonics

• Earthquakes
• Mountain building
• Volcanoes
• Islands