Transcript Plate Tectonics - Nogales High School

Plate Tectonics
Continental Drift
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Proposed by German
Scientist Alfred Wegener
in 1912.
Hypothesized that the
continents once formed
part of a single landmass
called a supercontinent.
This supercontinent began
to break up into smaller
continents about 250
million years ago.
Continental Drift
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Evidence from fossils proved that the continents had
once been joined.
Continental Drift
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Rock units found in different continents match even
though the continents are separated.
Continental Drift
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Wegener suggested
that if the continents
were once joined and
positioned differently,
evidence of climatic
differences would be
present.
Mid-Ocean Ridges
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Mid-Ocean Ridges are long, undersea mountain
chains that have a steep, narrow valley at the center
They form as magma rises, and create new ocean
floor as tectonic plates move apart.
Sea-Floor Spreading
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New ocean floor is formed
as magma rises to Earth’s
surface and solidifies at
mid-ocean ridges.
Paleomagnetism provides
evidence of sea-floor
spreading by showing the
magnetic symmetry of the
ocean floor rocks.
Continental Drift
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Explains why and how continents move.
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Earth’s crust is classified into two types:
Oceanic crust is dense and made of rock that
is rich in Fe and Mg which make it dense.
Continental crust is made of rocks that are
rich in silica and is low in density.
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Continental Drift
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Most scientists agree
that there are 15
major tectonic
plates.
The edges of these
plates are called
boundaries.
Boundaries are areas
that have frequent
earthquakes and
volcanoes.
Continental Drift Video
..\..\United Streaming\Continental_Drift.mov
Plate Boundaries
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The way that plates move relative to each other determines
hw the plate boundary affects Earth’s surface.
There are three types of boundaries: convergent, divergent
and transform.
Divergent Boundaries
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At divergent boundaries, two plates move
away from each other.
Magma from the asthenosphere rises to the
surface as the plates move apart.
The magma cools to form new ocean floor.
Creates a mid-ocean ridge with a rift valley.
Example: Atlantic Ocean, Red Sea
Divergent Boundaries
Convergent Boundaries
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As plates pull apart at one boundary, the push into
neighboring plates at other boundaries.
Convergent boundaries are boundaries that form
where two plates collide.
Convergent Boundaries
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Because oceanic crust
is more dense than
continental crust, three
types of collisions can
happen at convergent
boundaries.
Convergent Boundaries
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Oceanic-Continental Convergence – the more dense
oceanic crust will subduct under the continental
crust. This process results in mountain building and
volcanic activity. The Pacific Northwest coastline is
an example of this type of boundary.
Convergent Boundaries
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Oceanic-Oceanic convergence results in the
development of a deep ocean trench and island arcs.
The islands of Japan is an example of this type of
boundary.
Convergent Boundaries
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Continental-Continental convergence results in
mountain building such as the Himalayan
Mountains.
Transform Boundaries
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The boundary at which
two plates slide past
each other horizontally.
Results in earthquakes.
San Andreas Fault
Causes of Plate Motion
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The mantle moves in circular currents called
convection cells where warm magma rises
and cooler magma sinks down toward the
core.
This is caused by uneven heating from the
core.
The moving magma currents cause the plates
to move.
Spreading Zones Video
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..\..\United Streaming\Spreading_Zones.mov
The Changing Continents
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Continents break apart by the process of rifting.
Continents grow larger by developing terranes.
Subduction Zones Video
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..\..\United Streaming\Subduction_Zones.mov
Effects of Continental Change
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There are changes in climate due to the
continents position related to the equator and
other continents.
There are changes in living species when
geologic changes result in dividing and
separating species.
The Supercontinent Cycle
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The process by which supercontinents form and break apart
over time.
Pangaea formed about 300 mya and started to break up 250
mya.
Slowly the continents moved to their present postition
Current Plate Movements
Geography of the Future
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Africa will collide with Europe and the
Mediterranean Sea will close up.
East and West Africa will split and a new ocean will
form between them.
The Atlantic Ocean will close as North and South
America collide with Africa.
The section of Mexico and California that are west
of the San Andreas Fault will move towards Alaska.
In 250 million years, a new supercontinent will
form.
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http://mycontent.discoveryeducation.com/?pr
oductCode=US
http://www.learner.org/interactives/dynamice
arth/swfs/continents.swf
The End