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Wegener
1880-1930
earthobservatory.nasa.gov
Alfred Wegener first proposed the
theory of continental drift.
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 Continental drift was Wegener’s theory
that all continents had once been joined
together in a single landmass and have
drifted apart since.
 Wegener named this supercontinent
Pangaea.
 Wegener’s theory was rejected by
scientists because he could not explain
what force pushes or pulls continents.
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Fit of Continents
Across the Atlantic
Mountain ranges in
South America line
up exactly with
those in Africa!
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http://evolution.berkeley.edu/evolibrary/images/history/fossils3.gif
Notice how fossils lined up across continents!
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Amazing Facts: Did you know...
...that India was once in the Southern Hemisphere
connected to Antarctica?
...that North America was once surrounded by warm,
tropical seas?
...that Africa was once covered by glaciers, which were
kilometers in thickness?
...that the Sahara desert was once a tropical rain forest?
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An example of the proof for changing climate:
At one time,
the area that
is New
Mexico was
below the
equator!
As North America has drifted to different latitudes,
changing climates were experienced. This shows the
changes in the state of New Mexico.
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He could not find the force that was
causing the continents to drift.
Because of this, he could not convince
anyone that continents could move.
He died in Greenland on an expedition.
At the time of his death, no one believed
his hypothesis!
Technology developed during the 1940’s
changed all that!
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Discovery of Sea-Floor Spreading
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Sea-Floor
Spreading
m.y.
means
million
years ago
Notice this
compass. It
is important
for the next
slide
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http://platetectonics.pwnet.org/img/blocks.gif
As the sea floor spreads, the lava cools according to the
magnetic poles at the time. The rocks on the ocean
floor have proved that the earth’s magnetic field
sometimes reverses. The inner core flips and so the
north pole moves to the southern hemisphere! The
earthh itself does not flip.
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What causes sea floor spreading?
Convection currents!
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Click here for a hyperlink to an animation of convection
Be sure to click the play button!
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Animation of sea floor spreading
Can you explain this diagram!?
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The place where two plates move
apart or diverge is called a divergent
boundary.
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This is a model of sea floor spreading at a divergent
boundary called a mid ocean ridge.
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: www.ocean.udel.edu
Did you know that the Earth’s longest mountain range is
underwater and is called the mid-ocean ridge?
The Mid-Ocean Ridge system, shown above snaking its way
between the continents, is more than 56,000 kilometers (35,000 mi)
long. It circles the earth like the stitching on a baseball!
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A convergent boundary is where two plates
come together, or converge. The result of the
plates hitting together is called a collision.
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A transform boundary is a place where
two plates slip past each other, moving in
opposite directions.
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Oceanic crust to oceanic
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Continental crust to continental crust
collision
Before collision
India-Asia (Himalayas)
After collision
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from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270
Also the way the Appalachian Mountains formed!
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Because one plate gets pushed under
another, it is called subduction. This
is where volcanoes form!
Oceanic crust colliding
with continental crust
Oceanic crust
colliding with
oceanic crust
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all from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270
The process by
which the ocean
floor sinks
beneath a deepocean trench
and back into
the mantle is
called
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What causes an Earthquake?
An earthquake is the movement of Earth’s
crust resulting from the release of built-up
potential energy between two stuck
lithospheric plates.
The lithosphere is cold and brittle and can
fracture during an earthquake. The
lithosphere is divided into pieces called
tectonic plates. They are like broken ice
fragments that float on the surface of water.
Any sudden shifting of the tectonic plates
results in earthquakes. The tectonic plates
may slide past each other, push apart, or
collide together. The interactions at the plate
boundaries are important to consider.
(Notice the relationship in the previous
slides between the plate boundaries and
the location earthquakes
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Worldwide Earthquake patterns help us
know where the edges of plates are located
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The Earth’s Plates
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Here you see
the two slides
together.
What do you
see?
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Plate Boundary Map
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Earthquakes and Plate
Boundaries
Earthquakes commonly occur at
the boundaries of lithospheric
plates.
This is because plate boundaries
tend to be zones of (earthquake)
seismic activity
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Seismic data around Japan
(1960-2011)
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Seismic Data at the Pacific Rim
A region of seismic
volatility runs along the
Pacific rim called the Ring
of Fire. It marks the
boundary between a
number of huge tectonic
plates in the earth’s crust.
The pressure which builds
up when one plate pushes
against the other can lead
to violent volcanic activity
and powerful earthquakes.
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World Volcanoes Map
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Extremely high temperature and pressure cause the rock to melt and become liquid rock
How do Volcanoes
form?
Deep inside Earth, between the
molten iron core and the thin crust at
the surface (lithosphere), there is a
solid body of rock called the mantle.
When one tectonic plate is subducted
by another, rock from the subducted
plate melts, moves to the surface
through the crust, and releases pentup gases, volcanoes erupt.
Extremely high temperature and
pressure cause the mantle rock to
melt and become liquid rock
or magma. When a large body of
magma has formed, it rises through
the denser rock layers toward Earth's
surface. Magma that has reached the
surface is called lava.
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http://www.livescience.com/images/pangea_animation_03.gif
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