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P1
Bringing It All Together!
In the 1960s a third and final theory was proposed.
• This theory is a combination of...
Plate Tectonics
• The Theory of Continental Drift which states that ...
...the Earth’s continents were once together in one single
landmass, and have since drifted to their present position
when this super continent broke apart.
Plate Boundaries
• The Theory of Sea Floor Spreading which states that...
Unit Essential Question:
How does the Earth recycle and renew its surface?
...new ocean crust is formed at mid ocean ridges where
magma rises to the surface and destroyed at deep sea
trenches.
Presentation Objectives:
§ Define the theory of plate tectonics.
§ Explain how the Earth is divided into layers based on chemical and physical properties.
§ Define the asthenosphere and lithosphere.
§ Describe the plate motion at each of the three different plate boundaries.
§ Describe the features associated with each type of plate boundary.
§ Review density and use it to determine which plate will sink at a convergent boundary.
§ Explain how Earth’s surface is recycled.
Pie Slice of The Earth
Continental Crust
Oceanic Crust
Mostly Granite
Mostly Basalt
• The Theory of Plate Tectonics states that...
...the surface of the Earth is broken into large plates, the size and
position of which is changing over time.
P2
Mantle
Ultramafic
silicates
If we look at PHYSICAL PROPERTIES, such as viscosity, we get a
different set of layers.
Lithosphere
Asthenosphere
Lower Mantle
Outer
Core
Inner
Core
P3
Pie Slice of The Earth
Solid & Rocky
Soft Rock that flows
(like silly putty)
Solid
Iron & Nickel
Iron
The layers of the Earth that we have already discussed are based on the
CHEMICAL PROPERTIES of the layers.
Outer
Core
Inner
Core
Liquid
Solid
What is the Lithosphere?
The Plates of Plate Tectonics
The Lithosphere is made of the crust and the rigid upper mantle.
The Asthenosphere is made of the soft upper mantle.
Lithosphere
Continental Crust
P4
Oceanic Crust
Asthenosphere
Mantle
Lower Mantle
Outer
Core
Inner
Core
The lithosphere is broken into enormous pieces that we call plates.
Tectonic plates move in different directions and at different rates!
Plates interact at plate boundaries, creating characteristic features and processes.
Divergent Plate Boundaries
P5
• At divergent plate boundaries, the plates are moving AWAY
from each other.
• Important Facts:
• The spreading of the plates causes a crack in the surface in
the middle of the ocean or continent.
• New oceanic crust is created at a divergent boundary!
Divergent Plate Boundaries
P5
Rift Valley
• Important Features:
• Rift Valley - the top of the ridge where the plates actually
pull apart.
• In the ocean...
• On a continent...
• Mid-ocean ridge
• Continent Rift
• Underwater mountain chains.
• Continents split apart and a
• Ocean gets bigger!
new ocean forms.
Convergent Boundaries
P6
• At convergent plate boundaries, the plates are moving
TOWARD each other.
Subduction
P6
• Subduction is when one plate goes beneath the other.
• As the plate enters the asthenosphere, it melts.
• Resulting magma rises to the surface.
• When they meet, one typically sinks under the other.
• Which plate sinks depends on density!
• Which one will sink depends on the plate composition.
• There are two types of plates.
• Oceanic, which contains ocean floor made out of basalt.
• Continental, which contains continents made out of granite.
Basalt is MORE DENSE than granite.
• Which one will sink also depends on the age of the plate.
• Older plates are colder, and therefore are more dense.
Convergent Boundary: Ocean-Ocean
P7
Convergent Boundary: Ocean-Continent
Trench
Pla
te
1
Trench
Plate 2
Pla
te
1
Asthenosphere
• Important Facts:
•
Older plate is more dense so it subducts under the younger plate.
• Important Features:
P8
Plate 2
Asthenosphere
• Important Facts:
•
Oceanic plate is more dense so it subducts under the continental plate.
• Important Features:
•
Volcanic Island Arc - rising magma forms an arc of volcanic islands.
•
Volcanic Mountains - rising magma forms a chain of volcanic mountains on the
continent.
•
Deep Sea trench - the gap is created where the plate goes down.
•
Trench
•
Earthquakes - created when the plate slides underneath the other plate.
•
Earthquakes
Examples: Mariana Trench, Aleutian Islands and Japan
Examples: Andes Mountains, Mount St. Helens
Convergent Boundary: Continent-Continent
Plate 1
P9
Recycling!
A
Plate 2
B
P10
A
Asthenosphere
• Important Facts:
•
• New oceanic crust is created at divergent boundaries.
Continents are too light so neither plate subducts.
•
They buckle and fold upward instead!
• This crust moves away from ridge as more forms.
• The old oceanic crust continues to move until it reaches a
convergent plate boundary.
• Important Features:
•
•
Earthquakes - created when the plate buckle and deform.
Mountains - created when the surface is pushed upward as the plates collide.
• The old oceanic crust is subducted and destroyed.
Examples: Himalayas
Transform Boundary
Created at the same rate as it is destroyed so Earth remains the same size!
P11
• At transform plate boundaries, the plates slide past each other.
• Important Facts:
• When the two plates slide, they can slide vertically, horizontally or
both.
• Important Features:
• Fault - crack in the surface created by plate movement.
• Earthquakes - created when the plates slide past each other.
• Tsunamis - created when a plate shifts upward or downward in the
ocean.
Examples: San Andreas Fault