Transcript The Theory of Plate Tectonics

The Theory of Plate Tectonics
Chapter 4 Section 5
Key Terms
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Plate
Plate Tectonics
Fault
Spreading Boundary
Rift Valley
Colliding Boundary
Sliding Boundary
What are Tectonic Plates?
The cracks in the continents are similar
to the cracks in a broken eggshell.
 In the 1960’s, scientists proposed that
these cracks break the lithosphere into
separate sections called plates.
 The plates are responsible for carrying
the continents and ocean floor.
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How Plates Move
Plate Tectonics: the theory that states that
pieces of Earth’s lithosphere are in slow,
constant motion driven by the convection
currents in the mantle.
 The theory of plate tectonics explains the
formation, movement, and subduction of
Earth’s plates.
 The plates are carried along like ice is
carried on water.
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Plate Boundaries
The edges of Earth’s plates meet at plate
boundaries.
 Faults: breaks in the Earth’s crust where rocks
have slipped past each other.
 There are three kinds of plate boundaries.
 The plates move about 1 to 24 centimeters per
year.
http://www.youtube.com/watch?v=ifke1GsjNN0
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Type 1: Spreading Boundaries
Spreading boundary: where two plates move
apart.
 These are found along the edge of midocean ridges.
 Some can occur on land.
 A deep valley called a rift valley forms
along the spreading boundary.
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Type 2: Colliding Boundaries
Colliding boundary: the place where two plates
come together (aka convergent boundary).
 Collision 1: two plates of oceanic crust collide,
and the more dense plate sinks underneath.
 Collision 2: a oceanic plate collides with a
continental plate, and subduction occurs.
 Collision 3: two plates of continental crust collide,
but neither sinks. Instead, they push up mountain
ranges.
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Sliding Boundaries
Sliding boundary: a place where two
plates slip past each other, moving in
opposite directions (aka transform
boundaries).
 Crust is neither created nor destroyed.
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Plate Motions Over Time
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Scientists have seen evidence showing that
there were other super continents before
Pangaea.
Pangaea formed when Earth’s land masses
came together about 260 million years ago.
About 225 million years ago, Pangaea began
spreading apart.
http://www.youtube.com/watch?v=cQVoSyV
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