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Plate Tectonics
The Theory Unfolds!!!!
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Earth’s Layers
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Earth: built by distinct layers:
inner core, outer core, mantle,
crust; the crust is the thinnest
layer
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Earth’s Geologic
Timeline
Pre-Cambrian:
Paleozoic:
Mesozoic:
Cenozoic:
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Continents in Motion
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Alfred Wegener was a
German meteorologist that
proposed the theory (1912)
that the Earth was not
fixed - it "moved" on
plates. Come to find, in the
1960s, Alfred Wegner´s
theory was proven correct.
This theory is known as
__________________.
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Book written by Wegener
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In 1915, Wegener published his
evidence and conclusions in a
now classic book, Die entstehung
der kontinente und ozeane (The
origin of continents and oceans).
Wegener proposed that all
modern continents were once
assembled together in a
supercontinent he named
Pangaea.
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Continental Drift
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Theory that the
continents had once
been part of one or
more landmasses
that had separated
and moved apart.
They are supposed
to have broken up
about 200 million
years ago.
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Pangaea – Means “ All Earth”
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Wegener proposed that all continents had once
been joined in a supercontinent he named
Pangaea. Pangaea, he thought, had existed
from the primordial earth until the Mesozoic,
when it began to break up. Wegener at first
considered mantle convection as a possible
driving mechanism, but later rejected that in
favor of _______________ as the cause for
Pangaea's breakup and continental drift.
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Panthalassa – Means “All
Seas”
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245 Million years ago: Pangaea
existed when some of the
earliest dinosaurs were roaming
around this big earth. The land
Pangaea was surrounded by a
sea called Panthalassa.
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Pangaea breaks up Forming:
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Pangaea started to break up into two
smaller supercontinents during the
Jurassic period. By the end of the
Cretaceous period, the continents were
separating into land masses that look
like our modern-day continents.
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Evidence Supporting
Continental Drift
1.
These two widely separated continents seem to
resemble two separate pieces of a larger jigsaw
puzzle. North America, too, seems to mirror the
western coastline of Europe.
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Evidence Supporting
Continental Drift
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2.
– A small reptile that lived 270
million years ago that was found
in Eastern South America and
western Africa. Mesosaurus lived
near swamps and rivers and it
would have been impossible for
this reptile to have swam across
the Atlantic.
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Evidence of Continental Drift
3.
Fern fossils have
been found in Africa,
Australia, India, and
Antarctica.
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Evidence of Continental Drift
4.
Glacial striations on rocks show that glaciers
moved from Africa toward the Atlantic Ocean
and from the Atlantic Ocean onto South
America. Such glaciation is most likely if the
Atlantic Ocean were missing and the
continents joined.
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Evidence of Continental Drift
5.
The age and type of rocks in the coastal regions
of widely separated areas, western Africa &
eastern Brazil, matched closely.
Mountain chains such as the Appalachians and
Scandanavian Mtns. Of Greenland and Northern
Eupope seem to fit closely in age and structure.
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Wegener’s Theories Rejected
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Most scientist rejected Wegener’s theories --------Why ? ---------It was difficult to conceive of large
continents plowing through the sea floor to
move to new locations. What kind of forces
could be strong enough to move such large
masses of solid rock over such great
distances?
While in Wegener’s lifetime, he never found the
WHY to why the continents moved.
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Wegener suggested that the continents
simply plowed through the ocean floor, but
Harold Jeffreys, a noted English geophysicist,
argued correctly that it was physically
impossible for a large mass of solid rock to
plow through the ocean floor without
breaking up. Recent evidence from ocean
floor exploration and other studies has
rekindled interest in Wegener's theory, and
lead to the development of the theory of
plate tectonics.
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Definite Proof

But the purpose of the Glomar Challenger was
scientific exploration. One of the most important
discoveries was made during Leg 3. The crew
drilled 17 holes at 10 different sites along a
oceanic ridge between South America and Africa.
The core samples retrieved provided definitive
proof for continental drift and seafloor renewal at
rift zones. This confirmation of Alfred Wegener's
theory of continental drift strengthened the
proposal of a single, ancient land mass, which is
called Pangaea.
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This video can be found on My Big Campus…..It review the material I
covered in class
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Navy submarine commander
during World War II.
Harry Hess
Hess proposes sea-floor
spreading
1960
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Suggested that there was actually a break
at the center of the ridge known as a
________________________.
Magma from deep within the Earth was
coming to the surface at this Rift Zone and
creating new sea floor.
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Paleomagnetism
is a technique used to cross date ocean cores and to
establish major intervals over wide areas. By
measuring the polarity of the magnetism in samples it
is possible to determine the layer in which the Earth’s
polarity reverses.
Between periods of normal and reversed polarity.
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What is Sea-Floor Spreading?
In the early 1960s, Princeton geologist Harry Hess
proposed the hypothesis of sea-floor spreading, in
which basaltic magma from the mantle rises to create
new ocean floor at mid-ocean ridges. On each side of
the ridge, sea floor moves from the ridge towards the
deep-sea trenches, where it is subducted and recycled
back into the mantle
Types of Boundaries
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D i v e r g e n t Boundary
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A divergent boundary occurs where 2
plates are________________.
The force associated with this is
called – _______________.
Example – Mid-Ocean ridges where
Sea Floor spreading is occuring.
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Convergent Boundary: 3
Types
A convergent boundary is a boundary
between 2 colliding plates. When 2
plates collide one plate may dive
under the other plate at
a___________________.
There are 3 types.
1. Ocean – Ocean Convergence
2. Ocean – Continent Convergence
3. Continent – Continent Convergence
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Force associated with
Convergent Boundaries
What type of force is
associated with convergent
boundaries?
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Ocean – Ocean Convergence
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When two oceanic plates collide creating
deep sea trenches.
Example: Marianas Trench the deepest
part of the Pacific Ocean near the coast of
Japan at at 11033 meters (36201 feet)
deep.
Magma rises to form volcanoes or Island
arcs on the ocean floor parallel to the
trench.
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Ocean to Continent
Convergence
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The _____________ Oceanic plate
descends into the less dense Continental
Crust and SUBDUCTS its way down to the
Asthenosphere.
___________________ may form
Ex: The Andes in South America were
created when the Pacific plate ran into the
South American plate creating the Andes
Mountain Range.
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New crust is continually being pushed away
from divergent boundaries (where sea-floor
spreading occurs), increasing Earth's surface.
But the Earth isn't getting any bigger. What
happens, then, to keep the Earth the same size?
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In locations around the
world, ocean crust subducts,
or slides under, other pieces
of Earth's crust. The
boundary where the two
plates meet is called a
convergent boundary. Deep
trenches appear at these
boundaries, caused by the
oceanic plate bending
downward into the Earth.34
Continent to Continent Conv.
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Continental rocks have low densities
in which neither is more dense than
the other. This causes them to
buckle up and create Mountains
when they collide.
Very little volcanic activity.
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Earthquakes are CoMmoN.
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Ex: Appalachian’s and Himalayas
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Convergent – Convergent boundary
When two land masses meet neither will slide under the other. Instead,
the two crush together at what is known as a convergent boundary.
They crumple and fold. Some pieces of land are thrust over or under
other pieces. The result is a mountain range.
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The ______________, the highest mountains in the
world, were created this way. (In fact, they're still
growing.)
So were the European Alps.
Even the Appalachian Mountains formed when two land
masses came together. Although with the Appalachians, the
crushing ended long ago -- all that's left now are the eroded
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of a once high mountain range.
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Transform Fault Boundary
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Boundaries where plates are sliding
past one another in opposite
directions or in the same direction
but at different rates.
The Force associated with this
boundary is _____________.
Ex: San Andreas Fault in California.
YOU GET ________________ !!!
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Slippin' and a Slidin'
Transform boundaries neither create nor consume crust.
Rather, two plates move against each other, building up
tension, then releasing the tension in a sudden and often
violent jerk. This sudden jerk creates an earthquake.
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Convection Currents
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Convection
is
the____________________________________
___________________________. When fluid
is heated, it expands, lowering the density of
the heated material, causing it to rise through
the cooler fluid. As it rises, leaving the vicinity
of the heat source, in this case, hot magma near
the earth's surface, it will cool. When it
becomes more dense (because it is cooler) than
the surrounding fluid, it will begin to
sink.__________________________________
_________________________________.
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Arthur Holmes
believed a fluid mantle possessed convection
currents created by heat trapped beneath the Earth's surface.
Holmes hypothesized that convection currents welled up toward
the surface and then drug continents across the surface.
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Ocean Floor Map