Continental Drift
& Plate Tectonics
Alfred Wegener, a German scientist, proposed the
hypothesis of CONTINENTAL DRIFT, in 1912.
Hypothesis stated: All Earth’s continents were once
a single landmass (Pangaea) and then slowly
drifted apart.
Pangaea began to split 200 million years ago.
Evidence supporting Wegener’s Hypothesis
1. Fossils: a reptile, Mesosaurus, was found both in Eastern
South America and Western Africa only.
2. Climate changes: fossils of tropical plants have been found
on Greenland, indicating it might have once been close to the
equator.
3. Geology: Rocks found on one continent match up with rocks
on another continent, like a puzzle. Ex. Brazil to Western Africa.
THEORY OF PLATE TECTONICS
In the mid-1900’s, scientists
proved that the Earth was
made up of 18 moving
plates.
•Each plate is made of the
crust and the top part of the
mantle called the
LITHOSPHERE.
•The plates move on a layer
of hot, molten rock in the
rest of the mantle called the
ASTHENOSPHERE.
From Continental Drift came the....
http://curriculum.kcdistancelearning.com/courses/ENVSCIx-APU10/a/unit05/apes_5.c.4.html
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/earth.htm
Convection Currents transfer heat energy from the inner core to
the crust.
The rocks within the asthenosphere rise toward the crust when
heated, because they are less dense. Rocks begin to cool and
sink back again into the asthenosphere, as they become more
dense.
Old crust is being destroyed at the same rate new crust is formed = Earth stays the same size.*
What causes
plates to move?
divergent boundaries
Spreading centersSpreading centersSpreading centersSpreading centers are where 2 plates are moving away from are where 2 plates are moving away from are where 2 plates are moving away from are where 2 plates are moving away from
each other. each other. each other. each other.
New crust is formed here, as magma rises from the New crust is formed here, as magma rises from the New crust is formed here, as magma rises from the New crust is formed here, as magma rises from the asthenosphere.asthenosphere.asthenosphere.asthenosphere.
Results on Oceanic Crust: Mid-ocean ridgesResults on Oceanic Crust: Mid-ocean ridgesResults on Oceanic Crust: Mid-ocean ridgesResults on Oceanic Crust: Mid-ocean ridges
(Oceanic Crust splits apart) (Oceanic Crust splits apart) (Oceanic Crust splits apart) (Oceanic Crust splits apart)
1. 1. 1. 1. Mid-ocean RidgesMid-ocean RidgesMid-ocean RidgesMid-ocean Ridges: longest chains of mountains on : longest chains of mountains on : longest chains of mountains on : longest chains of mountains on
EarthEarthEarthEarth
a. Mid-Atlantic Ridge – 11,000 Km from Iceland to Antarctica; where the North & South American Plates are moving away from the Eurasian & African Plates.
Results on Continental Crust: Rift Valleys (hot magma pushes up on
Continental Crust, and the crust cracks as it stretches apart)
As the plates continue to pull apart, the valley floor sinks and becomes thinner.
Once the valley floor is below sea level, the valley fills with water.
Ex. Red Sea created by Arabian & African plates moving apart.
Great Rift Valley of Africa is being created as the
African Plate splits apart.
divergent boundaries
Iceland is being split into 2 islands from the Mid-Atlantic Ridge.
3 Types of Convergent Boundaries3 Types of Convergent Boundaries
1. Continental-Continental Collision occurs
where 2 plates carrying continental crust push
together.•Both plates are the same density, so neither will sink
beneath the other.
•This causes the plates to crumple and fold.
•Continue folding creates mountains.
Mt. Everest (29,035 ft) – Among the Himalayas
where the Indian & European Plates collided.
European Alps result of collision between
African & European Plates.
Convergent BoundaryConvergent BoundarySUBDUCTIONSUBDUCTION
2. Oceanic – Oceanic Subduction: This occurs when an older oceanic plate sinks (subducts) below another younger
oceanic plate. The older plate is pulled back into the asthenosphere because it is colder and denser.
Results:1. Deep-ocean trenches●Deepest places in the oceans; ●Thinnest part of the crust.
2. Island Arcs●Chains of volcanic islands that formabove deep ocean trenches.
2. Oceanic – Oceanic Subduction: This occurs when an older oceanic plate sinks (subducts) below another younger
oceanic plate. The older plate is pulled back into the asthenosphere because it is colder and denser.
Convergent BoundaryConvergent BoundarySUBDUCTIONSUBDUCTION
3. Oceanic – Continental Subduction: This occurs when an older oceanic plate sinks (subducts) below another younger
Continental plate. The older plate is pulled back into the asthenosphere because it is colder and denser.
Results:1. Deep-ocean trenches●Deepest places in the oceans; ●Thinnest part of the crust.
2. Volcanic Mountains●Chains of volcanic mountains that form along the edge of the continent.
Transform Boundaries
•Crust is neither created Crust is neither created Crust is neither created Crust is neither created
or destroyed.or destroyed.or destroyed.or destroyed.
•Two plates scrape past Two plates scrape past Two plates scrape past Two plates scrape past
each other as they each other as they each other as they each other as they
move in opposite move in opposite move in opposite move in opposite
directions.directions.directions.directions.
San Andreas Fault line
runs from the Gulf of
California through San
Francisco.
At the rate of movement,
LA will be part of San
Francisco in 10 million
years.
HOT SPOTSHOT SPOTS
Hot spots are stationary areas where material from deep within the mantle rises and then melts, forming magma.●They can be in the middle of a plate or along a boundary.●Volcanos form above the hot spot when magma erupts through the crust and reaches the surface.
Ex: Hawaiian Islands and Yellowstone Caldera
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