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Continental Drift

• I. Early Evidence of Continental Movement

A. Continental Drift
1. Continental Drift -
A hypothesis, which states that continents have
moved around the globe, over time, to reach their
current positions.
2. Alfred Wegener came up with this theory in
1912.
3. He believed that all continents were connected
as one large landmass about 200 million years
ago.
4. Then they broke and drifted to their current
positions.
5. He called this super land mass Pangaea.
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B. Wegeners Proof
1. Some continents look like they fit together.
2. Geological Clues
A.) Mountain Belts lined up. (ex. North America
Europe)
B.) Rock layers matched. (Ex. South America
Africa)
3. Fossil Clues
A.) Fossils of living things were found on
different continents that are separated by large
bodies of water.
B.) Ex. Mesosaurus found in S.America Africa.
Glossopteris found in S. America, India, Africa,
Antarctica.
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As the plate moves, the mountains grow
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4.Climate Clues
A.) He found coal deposits in N. America that
matched coal deposits in Europe.
B.) He found salt deposits in the desert part of
Africa.
C.) Glacial deposits in tropical regions like
India and Australia.
C. Modern Day Proof
1. Seafloor Spreading
A.) The theory states that magma travels to the
earths surface.
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http//scign.jpl.nasa.gov/learn/plate4.htm
B.) The magma forms cracks in the ocean floor.
C.) These cracks are called Mid-Ocean Ridges.
D.) The magma pushes out of the mid-ocean ridge.

E.) As the magma hardens it pushes the layers of
the ocean floor away from the mid-ocean ridge.
F.) The process then repeats it self.
D. Seafloor Spreading Proof
A.) The oldest layers of the Atlantic Ocean floor
are on the coastline of the continents. (180
million years old.)
B.) The youngest layers of the Atlantic Ocean
floor are in the center of the ocean. (50 million
years old)
C.) The Atlantic Ocean is getting larger.
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• II. Plate Tectonics

A. Layers of the Earth
1. Crust -
Thin, outermost layer of the earth.
2. Mantle -
Layer of the earth between the crust and outer
core.
Thickest layer of the Earth.
3. Outer Core -
Liquid layer of the Earth.
4. Inner Core -
Solid, inner most layer of the earth.
Structure of the Earth
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B. The Theory of Plate Tectonics
1. Plate Tectonics -
Is the theory that earths crust and upper mantle
are broken into sections that slowly move around
on the lower mantle.
2. Plates -
Sections of the earths crust and upper mantle
that move around on the bottom part of the
mantle.
3. The crust and upper mantle together are called
the lithosphere.
4. The lower mantle is called the asthenosphere.

5. The lithosphere is less dense than the
asthenosphere, so the lithospheric plates float
on top of the asthenosphere.
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C. Plate Boundaries
1. There are three types of plate boundaries.
When plates separate or move apart. (Divide)
A.) Divergent Boundaries -
When plates collide into each other.
B.) Convergent Boundaries -
C.) Strike-slip Boundaries -
When plates grind together and slide by each
other.
D. Why do plates move?
1. Plates move because of convection currents.
Is the movement of a fluid caused by differences
in temperature.
A.) Convection Current -
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2. Material close to the core is hot and has a
low density.
3. Material close to the crust is cool and has a
high density.
4. More dense material sinks and less dense
material rises causing a convection current.
5. When the material reaches the plates it pushes
them away or toward the plate boundary.
E. Effects of Plate Tectonics
1. The lithosphere is divided into seven major
plates and about ten smaller plates.
2. The interaction of the different plates causes
different land features.
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3. There are two different types of plates
Made from relatively light continental crust.
A.) Continental Plates -
B.) Ocean Plates -
Made from dense ocean crust.
4. Plate interaction land features
A.) Volcanoes -
Form when two ocean plates collide, or when an
ocean plate collides with a continental plate
causing the more dense plate to sink and melt.

Form when two continental plates collide. Since
continental plates are to light to sink the crust
thickens and is forced upward.
B.) Mountains -
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Form when any two plates separate. The ground
between them sinks and forms a valley.
C.) Rift Valley /Ridges-
Caused from any sudden movement of plates that
causes the plates to break.
D. Earthquakes -
E. Trench -
A deep V-shaped valley formed at the base of a
convergent plate boundary. (Ocean ocean
collision, or ocean continental collision.)

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