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Plate Tectonics
And
Continental Drift
Early Evidence for Continental
Drift
The Puzzle Like Fit of the
Continents
Alfred Wegener
• In the early 1900’s the German scientist
spent much of his life looking for evidence
to prove the continents drifted.
Pangaea
• Pangaea is the name Alfred Wegener gave
to the super continent that existed 250
million years ago.
Fossil Evidence
• Glossopteris is an extinct fern fossil found
in South Africa, Antarctica, Australia &
India
• Lystrosaurus is an extinct land reptile found
on different continents including Antarctica.
Geologic Evidence for
Continental Drift
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1. Glacier striations.
2. Igneous flood basalt.
3. Diamond and coal mines match up.
4. Magnetism in the rock.
1. Glacier Striations
• The glacier striations only make sense if the
continents are put together. Otherwise,
continental ice sheets would have originated
from the center of the ocean.
2. Flood Basalts
• Igneous flood basalts match up perfectly in
South America, Africa, and Antarctica. This
could have only occurred if the continents
were once together.
3. Coal Mines
• Coal mines form a straight “vein” through
Pangaea. This only makes sense if you put
the continents back together.
4. Magnetism in the Rocks
• The iron in the rocks record the location of
the North Pole when the magma or lava
cools. By looking at the latent magnetism
in the rock either the Magnetic pole is
erratic or the continents were once together.
Wegener Died with his Theory
• Alfred Wegener died in 1930 along with his
theory on continental drift.
• Scientist did not believe his theory because
he could not explain a force strong enough
to push the continents through the solid
ocean crust.
Modern Evidence
• After Wegener’s death new evidence was
found to support the theory of continental
drift.
Harry Hess & W.W. II
• With the invention of Sonar in W.W. II we
started making the first maps of the ocean
floor.
• Harry Hess was a Geologist and
commander in the Pacific. He was amazed
at the first sonar maps of the ocean floor.
Mid Atlantic Ridge
• The Longest Mountain chain on the planet
was found running through the center of the
Atlantic Ocean. This is called the Mid
Atlantic Ridge.
Exploration in the1950’s
• The Glomar Challenger was an exploration
ship that mapped the ocean floor and took
core samples.
Exploration 1970’s
• The submersible Alvin went down in the
deep Atlantic to study the Mid Atlantic
Ridge.
Pillow Lava
• In the center of the Mid Atlantic Ridge,
Alvin found a deep rift zone or crack.
Pillow lava was found coming out of this
rift.
Sea Floor Spreading
• Hot magma rises in the rift valley of the
Mid Atlantic ridge. This creates new sea
floor (Basalt) causing the Atlantic ocean to
expand.
Plate Tectonics
• The Mid Atlantic Ridge is the mechanism
by which the continents “drift” riding on the
mantle.
• The Earth’s internal heat is the driving
force behind plate tectonics.
The Plates
• Earth’s crust is broken up into plates. These
plates ride on top of the mantle or
asthenosphere.
Earthquakes & Volcanoes
• The distribution of earthquakes and
volcanoes outline the boundaries of the
plates.
Plate Boundaries
• There are 3 types of plate boundaries
• 1. Converging = colliding
• 2. Diverging = separating
• 3. Transform = sliding past each other
Two types of crust
• 1. Ocean crust is dense and made up of
basalt.
• 2. Continental crust is less dense and made
up of granite.
Diverging Zone
• The Mid Atlantic Ridge is an example of
two ocean plates diverging.
• The Red Sea is another example of sea floor
spreading.
• The continent of Africa is diverging forming
a rift and lake Victoria.
Iceland
• Iceland is a special place for geologist.
• This is where the Mid Atlantic Ridge has
actually risen above the sea forming
Iceland.
• There is a rift running down the center of
Iceland.
The Red Sea
• The Red Sea is growing wider every year.
This pushes Africa away from Saudi Arabia.
The African Rift
• Africa is the old center of Pangaea.
• It is still being ripped or rifted apart.
3 different Convergent Zones
• 1. Ocean Crust + Continental Crust
• 2. Ocean Crust + Ocean Crust
• 3. Continental Crust + Continental Crust
Convergent Zone #1
Ocean crust + Continental crust
• When dense ocean crust collides with
lighter continental crust the ocean crust is
forced underneath. This creates a deep
trench and a volcanic mountain range.
• Examples are the Cascades and the Andes.
Convergent Zone #2
Ocean crust + Ocean crust
• When two dense ocean crusts collide it
forms a deep ocean trench and a volcanic
island.
• Example: The Mariana’s trench and Japan.
Convergent Zone #3
Continental + Continental crust
• When two light continental plates collide
they create a large mountain range.
• India is being pushed into China forming
the Himalayan mountains.
Transform Fault
• Two plates slide past each other in a
transform fault.
• Transform faults can cause earthquakes.
• Example: San Andreas Fault.
The Driving Force
• The Earth’s internal heat is the driving force
behind plate tectonics.
• Hot spots in the mantle have created the
Hawaiian Islands.
Pangaea
• 250 million years ago Pangaea broke up.
• What about future projections of plate
movement????
The End