Transcript Plate Tectonics

Plate Tectonics
Moving Continents?
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The idea that the Earth's crust is not
completely stable is not new.
Understanding the WHY and HOW of this
has been a problem since the beginning of
geological studies.
1st Step
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Have to have evidence.
Way back in 1620 Francis Bacon noted the similarity of
the coastlines of Africa and South America.
In the 1800’s Antonio Snider-Pelligrini noticed similar
fossil plants in coal beds of Europe and North America
In 1908 Taylor and Baker noticed a correlation of global
mountain chains.
What is the problem?
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The discoveries these scientists made
were going against the belief that the
continents were stable and fixed.
To even think that the continents could be
moving was ridiculous to people in the
past and if a scientist were to propose it
they would be ridiculed.
The Start of Something New
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Alfred Wegener shocked the
world when he went against
common belief and
proposed his theory of
Continental Drift
He claimed that the
continents can move and
that all the continents had
once been joined to form
one large super-continent
called Pangaea (all land),
and the ocean was called
Panthalassia (all ocean)
Continental Drift
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Wegener was in his school library one
night when he found some scientific
articles describing the discovery of similar
fossil plants in coal beds of Europe and
North America.
Intrigued by the article Wegener began to
look for more occurrences like this.
Wegener’s Evidence
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His curiosity lead him
to discover multiple
lines of evidence that
he could use to
develop his theory.
What was his
evidence?
Puzzle-like Fit
Matching Fossils
Matching Mountain Chains
Matching Glacial Evidence
This Guy!
Continental Drift
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In 1915 Wegener published his theory of Continental
Drift with his supporting evidence, but it didn’t go over
so well.
"Can we call geology a science when there exists such
differences of opinion on fundamental matters as to
make it possible for such a theory as this to run wild.“
Wegener's theory is a fairly tale and should be ignored
due to its deleterious effect on students
What’s wrong with it?
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Wegener developed a theory with plenty
of supporting evidence, so what is the
problem with it?
Why wasn’t his theory excepted?
Objections
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HE HAD NO MECHANISM!!!!!!
Wegener developed his entire theory, but
forgot to think about how the continents
move.
He said that the continents “plowed”
through the ocean crust
Objections
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Wegener worked so hard to develop this theory
and because of his mechanism he was laughed
at and ridiculed
He was not respected in the science community
and his ideas were thought to be fairy tale
But Wegener did not give up
A Life of Finding the Truth
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Despite all of the criticism Wegener was
receiving he still went ahead and continued his
search for a mechanism
He knew that his theory was valid, but could not
find the mechanism
He devoted the rest of his life towards research
and discovery of the true reason how continents
move
Alfred’s Last Stand
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In 1930 Wegener went
on an expedition to
Greenland but never
came back.
All of his work went for
nothing and he received
no recognition for the
contributions that he
made towards science
Yes, it is a real squirrel and yes it is truly waterskiing!
Heading in the Right Direction
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Despite all of Wegner’s hard work he did not gain any
respect until well after his death
In the 1950’s and 1960’s discoveries about earthquakes,
magnetism, and the age of rocks on the ocean floor
added support to some of Wegener’s ideas.
Harry Hess
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WWII Naval Submarine
Officer (1939-1945)
Developed this idea of Sea
Floor Spreading.
He says that new ocean
crust is created at Mid
Ocean Ridges and old
crust is destroyed in deep
trenches.
How did he come up with this?
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While mapping the ocean floor Harry Hess
discovered a gigantic volcanic ridge system that
nearly stretched around the world.
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a ridge system 65,000 km long
the most extensive mountain range in the world
The Mid-Atlantic Ridge
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is the best known
divides Atlantic Ocean basin in two nearly equal parts
Atlantic Ocean Basin
One More Key Component
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In the 1960’s Drummond Matthews and
Frederick Vine (known as Matthews and
Vine) took a closer look at the ocean floor
and provided even more evidence to
support the idea of sea floor spreading.
Magnetic Reversals
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Earth has a magnetic
field
Similar to a giant dipole
magnet
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There is a magnetic north
and a magnetic south
Magnetic poles usually
match up with geographic
north and south.
Rocks and Magnetism
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Ocean crust is composed of a rock known as
basalt.
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Basalt is very rich in magnesium and iron.
Formed when lava cools at the surface
When the lava cools, the magnetic particles line
up with the magnetic poles of the Earth.
But Earth’s magnetic field isn’t always pointing
in the same direction.
Magnetic Reversals
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Earth’s present magnetic field
is called normal
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Magnetic north matches with
geographic north
magnetic south matches with
geographic south
At various times in the past,
Earth’s magnetic field has
completely reversed
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magnetic north matches with
geographic south
magnetic south matches with
geographic north
Matthews and Vine
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Matthews and Vine also noticed that the age of the
seafloor increased as you move from the mid-ocean
ridge towards the continents.
How do Matthews and Vine’s
discoveries relate to Seafloor
Spreading?
Tying it Together
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Seafloor spreading theory indicates that
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Oceanic crust is created at mid-ocean ridges (young)
Destroyed at trenches near continents (old)
This means that ocean crust is created in the
middle of the ocean, being pushed to the side
until it is destroyed in a trench.
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Magnetic reversals show that the ocean is spreading
from the middle with its symmetrical patterns of
magnetic reversals.
The seafloor gets older as you move from the midocean ridge outward which shows that new crust
forms in the middle and is destroyed on the outside.
SHHHHHHHHHHH!
Plate Tectonics
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The outer portion of the Earth, the lithosphere,
is composed of large irregular sections or plates
that “float” on the asthenosphere.
Terminology
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Lithosphere – “rock layer” – made up of
the crust and the uppermost part of the
mantle.
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This puts the “plate” in plate tectonics!
Asthenosphere – “weak layer” – made up
of the upper part of the mantle that the
lithosphere moves over top.
Plate Tectonics
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The continents are embedded in lithospheric
plates. As these plates move, they carry the
continents with them. The ocean basins are part
of lithospheric plates as well.
Plate Tectonics
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So, let me get this straight…..
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The outer portion of the Earth, the lithosphere
(crust and uppermost mantle), is broken up
into large irregular plates
These plates contain oceanic and continental
crust
The plates “float” on the asthenosphere
(upper part of mantle directly under the
lithosphere) carrying the continents on them
Hold Up
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Why do we care about plate tectonics?
Because it explains the distribution and
formation of volcanoes, earthquakes, and
mountains.
Assignment
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In front of you is a map of the world and a
chart with earthquakes, volcanoes, and
their longitude and latitude. You need to
plot each of these on your map putting an
“E” for earthquake in one color, and a “V”
for volcano in a different color. Once you
finish that you will need to answer some
guiding questions on the back.
Questions
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Do you notice any trends associated with the
location of the earthquakes and volcanoes?
Why do you think the volcanoes and
earthquakes are occurring where they do?
In a different color find three possible locations
for both volcanoes and earthquakes, then circle
them.
Look Familiar
Plate Tectonics
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As the plates move and interact at their
boundary they create things like
earthquakes, volcanoes, and mountains.
Moving Plates
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Remember that the Lithospheric plates are
floating on top of the asthenosphere.
The asthenosphere is the upper portion of the
mantle.
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What two layers is the mantle between?
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What do we know about these layers?
Mantle Convection
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The mantle is
undergoing
Convection.
Convection is the
transfer of heat
through movement of
a material.
Plate Boundaries
Three Types
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Convergent 
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Divergent  
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Transform 
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Convergent
Divergent
Transform
How fast are they moving?