Download Plate Tectonics

(Solid)
(Liquid)
(Viscous)
(Rocky)
The crust moves when the
mantle moves beneath it
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4 Pieces Evidence
1. Shape of the continents
 Continents seem to fit
together
2. Fossil Evidence
 identical fossils found in
Africa and South America
 suggests continents were
closer and connected
 - too large to be carried by the
wind
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- too fragile to survive the ocean
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- too far between the continents
3. Rock Evidence
 Rock formations and Coal fields in
Africa line up with matching
formations in South America
 Folded Mountain chain stretches
across South Africa and matches one
in Argentina
 Similar rocks and structures of the
Appalachian Mountains can be found
in the British Isles and Scandinavia
4. Climate
 Glacial deposits found in warm
climate --- therefore: areas were once
closer to the poles
 Salt deposits in Northern States --salt forms in tropical regions -- area
was once warmer
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Explains most geologic processes
Evidence of mid-ocean ridges and
ocean floor spreading helps explain
continental drift
Links together ideas of continental
drift and ocean floor spreading
Explains formations, movements,
collision and destruction of the
Earth’s crust
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Provides framework for
understanding:
◦ - Mountains
◦ - Volcanoes
◦ - Earthquakes
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- insights on how & why life on Earth
has evolved
- helps understand the past & predict
the future
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The upper mantle and the crust behave
as a strong rigid layer called the
lithosphere that is divided into plates
- slow continuous rate of movement – 5
cm/yr
- driven by convection currents in the
Earth’s mantle
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1) Divergent Boundaries – 2 plates
moving apart
2) Convergent Boundaries – 2 plates
moving together
3) Transform Fault Boundaries – 2 plates
that grind (slide) past each other
◦ the permanent magnetic field of a rock
that shows the direction of the magnetic
field at the time of the rocks formation
◦ when hot, minerals in newly formed rocks
align themselves with the earth’s magnetic
poles
◦ As the Earth’s magnetic poles change so
do the direction of the rock’s magnetic
poles
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strips of alternating polarity - mirrored on
each side of ocean ridges
Therefore: Each strip that has a different
polarity had to be formed at different time –
supports sea floor spreading
◦ A link between deep-focus
earthquakes and ocean trenches
◦ Shallow earthquakes occur near or at
the trench
◦ Deep earthquakes occur toward the
mainland
◦ Drilling of the ocean floor from the mid
ocean ridge toward the coast lines
◦ Oldest rocks were found closest to the
shoreline, youngest nearest the ridge
◦ Therefore: The ridge is producing new
oceanic crust while older crust is being
pushed toward the shoreline
◦ Rising magma from the mantle produces
volcanoes along the floor of the ocean
◦ As plates move, new volcanoes are formed
along the floor bottom above the hot spot
◦ Hawaii – age of features increase as you move
away from the hot spot (Kilauea)
◦ Therefore: The plates are moving over the hot
spot and forming new volcanic features.
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Convection Currents basic driving force
◦ Hot, less dense magma rises toward the
crust while cooler, more dense magma
sinks
◦ Plates move because of the uneven
distribution of the Earth’s heat
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The pulling of old crust down in the mantle
because by the downward flow of more dense
magma in the convection current
The down-ward pull, from gravity, on the
oceanic lithosphere at the ridge
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http://www.youtube.com/watch?v=ryrXAGY1
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