Download The Theory of Plate Tectonics

The Theory of Plate
Tectonics
3.3
What is the Theory of Plate Tectonics?
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Hard boiled egg analogy
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Earth’s crust pieces = plates
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Plates meet at boundaries
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Plates move in 1 of 3 ways
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Divergent Boundary = plates move apart
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Convergent Boundary = plates come
together
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Transform Boundary = plates slip past each
other
The theory of plate tectonics states that
Earth’s plates are in slow, constant motion,
driven by convection currents in the mantle.
Mantle Convection and Plate Motions
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Plates move b/c they are
on top of large convection
currents in the mantle
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Subduction – gravity pulls
denser plates down into
the mantle
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The rest of the plate is
also moving towards the
point of subduction
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Similar to a pot of soup on
the stove
Plate Motions Over Time
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Satellites measure plate
movement
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Slow: 1-12 cm per year
N/A and Eurasian plates move
apart roughly 2.5 cm per year
(fingernails growth)
u Millions of years = great distance
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Earthquakes, volcanoes,
mountains, DOT
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Several supercontinents
including Pangea
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Pangea formed 250-300 million
years ago
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200 million years ago it broke up
Plate Boundaries
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Faults: breaks in earth’s
crust where rocks have
slipped past each other
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Plates collide, pull apart,
or grind against each
other (slip)
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Great changes such as
volcanoes, mountain
ranges, and DOTs
Divergent Boundaries
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Plates move apart from
each other
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Iceland = walk between
plates (picture)
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Most are at MOR = SFS
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Few places = MOR rises
above sea level
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Plates diverge on land =
rift valley forms
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East Africa
Convergent Boundaries
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Plates collide
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Density determines which plate goes
up/down
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2 oceanic plates converge = DOT
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1 oceanic plate and 1 continental plate
converge = oceanic plate (denser) goes down
pushing the continental plate up
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Volcano formaton:
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Water escapes the oceanic crust – into
the mantle
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Lowers the melting point
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Mantle melts and rises up as magma
Transform Boundaries
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Plates slip or grind past each other
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Moving in opposite directions
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Sides of plates = rocky and jagged
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Grab hold of each other and lock in
place
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Forces inside the crust = unlock
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Earthquakes result
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Crust is neither added or taken
away
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Ex: San Andres Fault