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Transcript
PLATE TECTONICS
The Earth’s Crust is in Motion
4 Main Layers of the Earth


Crust– Made up of two types: Oceanic and
Continental. Contains mostly Silicon,
Oxygen, and Aluminum
Mantle– Divided into upper and lower
mantle; mostly Iron and magnesium

Outer Core– Liquid, mostly Iron and Nickel

Inner Core– Solid, Mostly Iron and Nickel
Comparison of Earth’s Two Types
of Crust

Oceanic



Continental
_Thin_______ and more
dense
Made up mostly of
_Basalt______
Thicker and _Less_____
dense
 Made up mostly of
__Granite________

Theories Prior to Plate Tectonics

Continental Drift


Proposed by
_Alfred ___
_Wegener______
Says that the
continents have
_Drifted/Plowed__
______ to their
present location
Evidence for Continental Drift


Continents fit
together
Fossils



Continents fit like a puzzle
Large landmass called
_Pangaea_______
Fossils of animals such as
_reptiles______ and plants
like ___ferns______ were
found on different
continents.
Movement of the Continents
Evidence for Continental Drift
(continued)

Climate



Rock Type and
Structure

Warm-weather fossils
found in the
Arctic_______
Evidence of
_glaciers______ found
in present-day warm
areas.
Same rock types and
structures on different
continents
Why was Wegener’s Original
Proposal of Continental Drift not
Accepted?
STOP HERE!!
Theories Prior to Plate Tectonics
(continued)
• Seafloor Spreading
• Proposed by Harry
Hess.
• Says that hot, less
dense material in the
_mantle__ is forced
upward at _midocean ridges.
Seafloor Spreading (continued)
• As magma is forced upward at mid-ocean
•
•
ridges, it flows in _opposite_______ directions
away from the ridge.
As it moves away from the ridge, the magma
cools, solidifies, gets __older______and
becomes _more_____ dense.
Becoming more dense than the __mantle______
below it, the oceanic crust sinks downward at
convergent boundaries, forming _subduction
zones_____
Evidence for Seafloor Spreading
• Age of the Seafloor
• Oceanic crust is
•
_younger______ than
continental crust
Oceanic crust is _250___
million years old while
continental crust is
almost _3__ billion years
old. Rocks are younger
at the mid-ocean ridge
and get increasingly
_older__ away from the
ridge on both sides
Evidence for Seafloor Spreading
(continued)
• Magnetic Clues
• _Magnetic__ minerals in
•
basaltic rocks align with
the Earth’s _magnetic_
field.
The magnetic field has
__reversed__ several
times.
Theory of Plate Tectonics
• Continental and Oceanic crust is broken
up into sections called _plates______ or
_tectonic___ plates that move over the
Earth’s surface.
Layers Related to Plate Tectonics
• Lithosphere
• Consists of the
•
• Asthenosphere
•
•
_crust__ and rigid
upper mantle_
Broken into large
pieces called plates.
_”Plastic”_-like part of
the upper mantle.
Convection_ occurs
here.
Tectonic Plate Boundaries
• 3 Main Types of
Boundaries
• Divergent – plates
•
•
move away from each
other
Convergent – plates
move toward each
other
Transform – plates
slide past each other
horizontally
Divergent Boundaries
• Plates move _away_ from each other
• Examples of divergent boundaries are the
Mid-Atlantic _Ridge______ and the EastPacific _Rise___.
• This is where _Convection_ occurs.
A plume of hot magma rises from deep within the mantle
pushing up the crust and causing pressure forcing the
continent to break and separate.
Lava flows and earthquakes would be seen.
As the rift valley expands two continental plates
have been constructed from the original one. The
molten rock continues to push the crust apart
creating new crust as it does.
As the rift valley expands, water collects
forming a sea.
The sea floor continues to spread and the
plates get bigger and bigger.
Convergent Boundaries
• Plates Move
_Toward_______Each
Other
• Three Types of
Convergent
Boundaries
1) Oceanic-to-Continental
2) Oceanic-to-Oceanic
3) Continental-toContinental
Oceanic-to-Continental Convergent
Boundaries
• More dense _oceanic___ crust subducts
under the less dense _continental___
crust.
• Characteristics include:
- _Trenches__ at subduction zone
- Volcanoes
- _Deep Earthquakes_____
Andes Mountains in South America
Oceanic-to-Oceanic Convergent
Boundaries


An _older_, cooler, and _more_ dense
oceanic plate _subducts__ under another
oceanic plate
Characteristics include:
- Volcanic
- Earthquakes
- Trenches
Aleutian Island Chain, Alaska
Aleutian Mountains
Pavlof Volcano
Continental-to-Continental Convergent
Boundary



Two _continental__-crust plates collide.
Since continental material is _equally_
dense, movement is mostly _upward__.
Characteristics include:
- Tall mountains
- Earthquakes
Continental-to-Continental
Convergent Boundary
Collision of India and Asia
Himalaya Mountains
Transform Plate Boundaries



Tectonic plates _slide __ _past_ each
other with little or _no_ _vertical_
movement or subduction
Characteristics include:
- _Major_ Earthquakes
An example of a transform boundary
is the _San_ _Andreas__ fault in
California
Transform Boundary Example
Diagram of Transform Boundary
Example of Transform Boundary
Plate Boundary Summary
Other Characteristics of the Plate
Tectonics Theory


Volcanoes and Earthquakes are
concentrated along _Plate_
_boundaries____
An example is the “_Ring_ _of_
_fire_” around the Pacific Ocean
Earthquakes are Also Concentrated Along Plate
Boundaries
Hot Spots!
• An EXCEPTION to volcanoes and
earthquakes occurring along plate
boundaries are _hot_ _spots__
• These occur where magma rises to the
surface away from a plate boundary.
• An example is the _Hawaiian___
_Islands_.
Plate Moves over Hot Spot,
Creating an Island Chain
Map of Island Chain Created by the
Hawaiian Hot Spot
What Causes the Plates to Move?
• The cause of tectonic (lithospheric) plate
movement is _convection_ _currents____
in the plastic-like mantle, or the
_Asthenosphere_