Plate Tectonics

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Plate Tectonics

• EQ What is the theory of plate tectonics?

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Plates
EQ What is the theory of plate tectonics?

• A section of the lithosphere that slowly moves,
  carrying pieces of continental and oceanic crust
• The plates fit closely together along cracks in
  the crust
• Plates carry the continents or parts of the ocean
  floor, or both

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Scientific Theory

• A well tested concept that explains a wide
  range of observations

EQ What is the theory of plate tectonics?
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Plate Tectonics

• A geological theory that states that pieces of
  Earths crust are in constant, slow motion,
  driven by convection currents in the mantle
• Convection Currents The movement of a fluid,
  caused by differences in temperature and density,
  that transfers heat from one part of the fluid to
  another

EQ What is the theory of plate tectonics?
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How can Earths plates move?

• The plates of the lithosphere float on the top of
  the asthenosphere
• Convection currents rise in the asthenosphere and
  spread out beneath the lithosphere
• Geologists believe this causes plate movement

EQ What is the theory of plate tectonics?
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As plates move, they collide, pull apart, or
grind past each other, producing spectacular
changes in the earths surface.
EQ What is the theory of plate tectonics?
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These changes include volcanoes, mountain ranges,
deep sea trenches, and earthquakes.
EQ What is the theory of plate tectonics?
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Figure 26 Interpreting MapsWhich plates include
only ocean floor? Which plates include both
continents and ocean floor?

• Plates that include only ocean floor are the
  Pacific Plate and the Nazca Plate
• All other labeled plates in the figure include
  both continents and ocean floor

EQ What is the theory of plate tectonics?
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Study the map of Earths plates in Figure 26.
Notice the arrows that show the direction of
plate movement. Now find the Nazca plate on the
map. What direction is it moving?

• The Nazca plate is moving east

EQ What is the theory of plate tectonics?
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Find the South American plate and describe its
movement.

• The South American plate is moving west

EQ What is the theory of plate tectonics?
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What do you think will happen as these plates
continue to move?

• If the plates continue to move, they will collide
  (convergent boundary)
• Since the Nazca plate carries oceanic crust and
  the South American plate carries continental
  crust, the Nazca will plunge beneath the South
  American plate

EQ What is the theory of plate tectonics?
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Faults

• A break in the Earths crust where slabs of rock
  slip past each other

EQ What is the theory of plate tectonics?
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three types of plate boundaries
EQ What is the theory of plate tectonics?

• Transform Boundaries
• Divergent Boundaries
• Convergent Boundaries
• At each type of plate boundary, there is a
  different type of plate movement

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Transform Boundaries

• A plate boundary where two plates move past each
  other in opposite directions
• Crust is neither created nor destroyed

EQ What is the theory of plate tectonics?
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What Earth changing event occurs on a
transforming boundary?

• Earthquakes frequently occur at transform
  boundaries

EQ What is the theory of plate tectonics?
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Divergent boundaries

• A plate boundary where two plates move away from
  each other
• Most divergent boundaries occur at the mid-ocean
  ridge
• Divergent boundaries that occur on land are
  called rift valleys
• Example Great Rift Valley (South Africa)
• A 3,000 km crack in the earth

EQ What is the theory of plate tectonics?
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Rift Valleys
EQ What is the theory of plate tectonics?

• A rift valley is a deep valley that forms along a
  divergent boundary on land
• Rift valleys form as two slabs of Earths crust
  slide apart

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What could eventually happen at the Great Rift
Valley in Africa?

• The rift may someday split the eastern part of
  Africa away from the rest of the continent

EQ What is the theory of plate tectonics?
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Convergent Boundaries

• A plate boundary where two plates move toward
  each other
• Collisions can occur between
• oceanic crust and oceanic crust
• oceanic crust and continental crust
• continental crust and continental crust

EQ What is the theory of plate tectonics?
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When two plates collide, the density of the
plates determines which one comes out on top.
EQ What is the theory of plate tectonics?
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What occurs when plates carrying oceanic crust
collide?

• The more dense plate dives back into the mantle
  (subduction)
• The collision between oceanic plates causes
  deep-ocean trenches

EQ What is the theory of plate tectonics?
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What occurs when plates carrying oceanic and
continental crust collide?

• The more dense oceanic crust sinks and plunges
  (subducts) beneath the less dense continental
  crust
• The collision between oceanic plates and
  continental plates can cause a volcanic eruption

EQ What is the theory of plate tectonics?
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What occurs when plates carrying continental
crust collide?

• Plates crash head on causing mighty mountain
  ranges

EQ What is the theory of plate tectonics?
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What types of plate movement occur at plate
boundaries?

• Plates slip past each other at transform
  boundaries
• Move apart at divergent boundaries
• Come together at convergent boundaries

EQ What is the theory of plate tectonics?
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Plates move at a rate of between one and ten
centimeters per year.
EQ What is the theory of plate tectonics?
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The North American and Eurasian plates float away
from each other at a rate of fingernail growth.
This is a rate of 2.5 centimeters per year.
EQ What is the theory of plate tectonics?
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Figure 29 Posing QuestionsWhat questions would
you need to answer in order to predict where the
continents will be in 50 million years?

• You would need answers to how fast and in what
  direction each plate is moving

EQ What is the theory of plate tectonics?