Plate Tectonics

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Plate Tectonics
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What Did The Earth Look Like In The Past?
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CONTINENTAL DRIFT THEORY

• Alfred Wegener - 1912 - developed theory of a
  large land mass called Pangaea (means all land).
  The ocean was called Panthalassa. He thought
  Pangaea broke apart and floated on the ocean
  floor due to earths rotation.
• Evidence of proof fossils of plants animals,
  rocks, glacial clues, matching climate and
  continents fitting together like a puzzle.
• Theory was ignored because there was no
  explanation of how, when, or why these changes
  took place.

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Evidence of Continental Drift
GLOSSOPTERIS - G Fossil plant /Similar climate
LYSTROSAURUS - L A small reptile
C/W
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ROCK CLUE - R Rock structures are similar types
ages
R
CLIMATE - C Warm weather plants
GL
R
G
GL
G
L
GL
G
R
R
M
L
GLACIERS - GL Glacial deposits Rock surfaces
scoured polished by glaciers
G
GL
M
L
G
MESOSAURUS - M Freshwater/Land reptile
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Principle of Uniformitariantism - states that the
processes we see changing Earths surface today
are the same as those that changed it in the
past. Principle of Superposition - states that
layers of sedimentary rock near the surface are
younger than layers of rock deeper down, unless
something Has disturbed the layers. Unconformity
- is a place where rock layers are missing.
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In 1968, scientists aboard the research ship
Glomar Challenger drilled into the seafloor for
rock samples. They discovered that the youngest
rocks were located on the mid-ocean ridge in
the Atlantic Ocean. The rocks became older as
they moved farther away from the ridge.
PLATE TECTONICS
This gave evidence to the theory of seafloor
spreading that was suggested by a Princeton
University scientist, Harry Hess. Hess was on a
Navy vessel in WW II, mapping the ocean floor
with a fathometer - a type of sonar that used
echo sounding to help ships know where the
bottom of the ocean floor was. He proposed that
hot, less dense material below the crust rises
toward the surface at the mid ocean ridges,
flowing sideways, carrying the seafloor away
from the ridge in both directions.
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Divergent plates spread apart from each
other, creating new crust. Hot, molten magma
rises to the surface of the ocean floor, pushing
the floor outward. On the Mid- Atlantic Ridge,
the North American plate is moving away from
the Eurasian and the African Plates. This
process is making the Atlantic Ocean larger.
The Great Rift Valley in eastern Africa is
becoming a divergent plate boundary. Iceland is
also. When new seafloor is created
by this plate movement, the magma cools
quickly, forming a crust made of basalt
rock. This creates a very heavy,
dense crust, even though it is only 3
miles thick.
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SEAFLOOR SPREADING
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Names of Plates
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The Earths crust appears to be broken into
pieces like a puzzle, which are called plates.
These rigid plates are being moved by the
convection currents in the hot, molten mantle.
The plates spread apart, collide or slide past
each other, causing earthquakes, volcanoes,
mountains and ridges. The plates can move 2 to
15 centimeters each year.
PLATE TECTONICS
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Plates Move Away From Each OtherThis is called
Divergence these are constructive boundaries
since they produce new land
Africa and Arabia
North America and Eurasia
Mid-Atlantic Ridge
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Divergence Moving Apart
Rift Valley if the land is above water
Sea Floor Spreading when the land is below water
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Plates Move Toward Each OtherThis is called
Convergence these are destructive boundaries
since they deform the plates
Convergent
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Folded Mountains
Subduction
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Continent/Continent
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Ocean/Continent
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Convergent
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Andes Mountains
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Ocean/Ocean Subduction
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Convergence Moving Together
Trenches
Mountains
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Structural Mountains
Volcanic Mountains
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A convergent boundary is created when two plates
collide into each other. When this occurs,
mountains and/or volcanoes are created and
earthquakes can happen. When the heavier
oceanic floor collides into the lighter
continental crust, the continental crust is
pushed over the oceanic crust. The oceanic
crust dives under the continental crust
creating a subduction zone. Land is lost in
this area. The Pacific Ocean is getting smaller
because of this process.
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Rock parts pulled Apart from faults
Sierra Teton Range
Mountain Formation
Rock layers folded Or compressed
Appalachians
Plates sink and Melting occurs Lava piles up From
magma
Hawaiian Islands
Rocky Adirondack
Forces in Earth Push on crust
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Active Movements - Faults
One day Los Angeles and San Francisco will be
next to each other
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Transform
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Shearing
TRANSFORM FAULT
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This type of boundary occurs where two plates
slide past one another. They move in opposite
directions or in the same direction at different
rates. When one plate slips past another
suddenly, earthquakes occur.
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FAULTS are fractures or break in earths crust -
movement has taken place - rock strata layers do
not match - create mountains- Niagara Falls.
Blocks are pulled apart overlying block
moves down the fault plane. A spreading
zone. Sierra Nevada's
Hanging Wall
Foot Wall
Squeezing or compressing Blocks are pushed
together Moves up the fault plane. Himalayas Mts.
- India
Foot Wall
Hanging Wall
Transform - strike - slip fault - a lateral
fault Slide past each other. San Andreas, CA.
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CONVERGENT
CONVERGENT
LAND
OCEAN
DIVERGENT
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Earthquakes Volcanoes
Earthquakes, Volcanoes Mountains
Earthquakes
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Mid ocean ridge
Mid-Atlantic Ridge
Sea floor spreading
Divergent
Rift Valley
Iceland
Collision of Ocean-ocean
Island arc
Convergent Ocean-ocean
Convergent
Trench
Subduction
Collision of Continental/ oceanic
Convergent
Trench
Andes Mountains
Volcanic mountains
subduction
Himalaya Mountains
Collision of Continental/ continental
Folded mountains
Convergent
Transform
Shearing
Transform fault
San Andreas fault
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Types of Boundary convergent, divergent,
transform Choices of Motion at Boundary
collision of continental/continental Collision
of oceanic/oceanic Collision of
continental/oceanic Ocean floor
spreading Shearing Subduction Land Features
Formed - Island arc Folded mountains Mid-ocean
ridge Rift valley Transform fault Trench Volcanic
Mountains Actual Examples Andes
Mountains Aleutian Islands Himalaya
Mountains Iceland Mid-Atlantic Ridge San Andreas