Chapter 4 Plate Tectonics
Section 1
Lesson Objectives
Identify the
layers of the
earth by
composition
Identify the
layers of the
earth by their
physical
properties
Describe Plate
Tectonics
Identify the layers of the
earth by composition
Keywords
Crust
Mantle
Core
Lithosphere
Asthenosphere
Mesosphere
Tectonic Plates
Composition
Physical Structure
Seismic waves
Identify the layers of the
earth by their physical
properties
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Composition, Physical Structure
Earths Layers:
Divided 2 different ways:
1. Composition (What it’s made of)
2. Physical Structure (Ex: solid or liquid)
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Describe Plate Tectonics
Keywords: Crust, Mantle, Core
Three layers based on composition:
1. Crust
2. Mantle
3. Core
Note: Denser material collects in the
core because denser objects
always sink due to gravity.
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Core
The Core
1. Makes up 33% of the
Earth’s mass
2. Mostly Fe with some
Ni (the denser
elements)
3. Little to No: O, Si, Al &
Mg
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Mantle
The Mantle
1.
2.
3.
4.
5.
Between the core and crust
Contains most of the Earth’s
mass (67%)
Mostly Mg & Fe with some Si,
O, & Al (more Mg than Al,
because Mg is more dense)
Temperature = 870oC – 2200oC
Composition studied from
volcanic eruptions
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Describe Plate Tectonics
Keywords: Crust
The Crust
•
Thin & solid, outer most layer (5
– 100 km thick)
• up to 870oC (increasing with
depth)
• Continental Crust: Often
composed of granite; mostly Si,
O, Al, Ca, Na, K; thick & less
dense
• Oceanic Crust: Usually
composed of basalt; mostly Si,
O, Fe, Mg; thin & more dense
• Why does oceanic
crust sit lower than
continental crust?
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Describe Plate Tectonics
Keywords: Lithosphere, Asthenosphere, Mesosphere, Outer Core, Inner Core
Physical Structures of the
Earth
• Five layers based on Physical
Properties
1. Lithosphere
2. Asthenosphere
3. Mesosphere
4. Outer Core
5. Inner Core
1
2
3
5
4
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Lithosphere, Asthenosphere, Mesosphere
Lithosphere
•
•
2 parts: rocky crust and rigid,
outermost mantle
TECTONIC PLATES!!!!
Asthenosphere
• Plastic (flowing) upper mantle
directly beneath the lithosphere
Due to heat and pressure
Mesosphere
• Strong, dense lower layer of the
mantle
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Outer Core, Inner Core
Outer Core
• molten Fe & Ni – produces Earth’s
magnetic field
• Surrounds Inner Core
• Temperature = 2200-5000C
• Less pressure than inner core
Inner Core
• Solid Fe & Ni
• Temperature = 5000oC
• Extreme pressure
Why do you think the outer core is
liquid, when the inner core is solid?
Describe Plate Tectonics
How do we know
about these
layers?
By the
motion of
seismic
waves
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Keywords: Seismic Waves
Mapping the Earth’s Interior
•
When earthquakes occur,
seismic waves (vibrations)
are sent out in all
directions, through the
earth.
•
These vibrations reach
different places at different
times because of the ways
the wave bend and change
speed as they pass through
the earth’s layers
Describe Plate Tectonics
Identify the layers of the
earth by composition
Identify the layers of the
earth by their physical
properties
Describe Plate Tectonics
Keywords: Tectonic Plates
Tectonic Plates:
• Pieces of lithosphere that move
around on top of the
asthenosphere
Major Tectonic (lithospheric) Plates
• Pacific Plate
• North American Plate
• Cocos Plate
• Nazca Plate
• South American Plate
• African Plate
• Eurasian Platet
• Indian Plate
• Australian Plate
• Anarctic Plate
Tectonic plates are constantly moving.
The fastest plate moves at 15
centimeters (6 inches) per year while
the slowest plates move at less than 2.5
centimeters (1 inch) per year.
Lithospheric Plate Cross Section
1) Both oceanic and continental plates float on top
of the asthenosphere, like ice cubes floating in
water, because of their…
Lower density
2) Just like ice cubes, the
plates can move around
and often bump into
each other.
3) Some of the plate sits
below the level of the
asthenosphere, just like
ice displacing water.
The thicker continental
crust displaces more of the
asthenosphere than
oceanic crust.
Section 2
Lesson Objectives
Describe
Wegner’s theory
of continental
drift
Explain seafloor spreading
and magnetic
reversals
Describe how
new oceanic
lithosphere
forms at midocean ridges
Describe Wegner’s theory
of continental drift
Keywords:
Continental drift
Pangea
Sea-floor spreading
Mid-ocean ridge
Magnetic reversals
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Keywords: continental drift, Pangea
Alfred Wegener
• Proposed idea of
Continental Drift
Continental drift
hypothesis
• Supercontinent called
Pangaea (greek for “all
earth”) began breaking
apart about 200 million
years ago
• Continents broke apart
and then "drifted" to
present positions
(November 1, 1880 – November 1930)
Describe Wegner’s theory
of continental drift
Keywords: continental drift
Evidence of Pangea and
continental drift
1.
2.
3.
4.
5.
Fossil evidence
Glacial scars
Coal deposits
Mountain rages
Paleoclimate
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Describe Wegner’s theory
of continental drift
Keywords:
Wegener’s matching
of mountain ranges
on different
continents
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Paleoclimatic (Ancient Climate) evidence
To Do…
• Complete reconstructing Pangea activity
Glossopteris
Mesosaurus
Lystrosaurus
Glacial Striations (scars)
Coal Deposits
Mountain Ranges
• Pangea split into
Laurasia and
Gondwana during the
Triassic period
Earthquake Activity:
Proof the Plates Exist
Earthquake Depths and Locations around the World
Lithospheric Plates of the World
More proof the plates move:
Hot spots can create new land
• New land that is not formed at plate boundaries
Complete Hot Spot Activity
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Keywords: continental drift
Why was Wegener’s hypothesis rejected?
• People couldn’t observe the plates moving
• The main objection to Wegener's proposal was its
inability to provide a correct mechanism
• In other words, he couldn’t explain HOW and WHY
the continents drift.
• Wegner did not have a good reason for the driving
force of movement of the plates.
• He claimed it was the same forces that influence
tides (gravity).
Where was Wegener missing evidence from?
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Keywords: sea-floor spreading, mid-ocean ridge,
Mid-ocean ridges
• Underwater mountain
chains
• Where sea-floor spreading
takes place
• As plates move away from
each other, sea floor
spreads and magma rises to
fill the gap
• Older crust is farther away
from ridge than younger
crust is
Describe how new oceanic
lithosphere forms at midocean ridges
Sea Floor Spreading
rift valley
mid-ocean ridges
newer less dense crust
older more dense crust
lithospheric plate
magma
asthenosphere
Sea Floor Spreading
• A rift valley is volcanically active forming new
oceanic crust on each side of the valley creating MidOcean Ridges.
• The new crust pushes the older crust away from the
mid-ocean ridge, moving the ocean floor & the
continents
• Ex: Mid-Atlantic Ridge
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Keywords: magnetic reversals
Evidence of sea-floor spreading
• Magnetic reversals
• When earth’s magnetic poles change
• North and south magnetic poles have changed many
times throughout history
• Molten rock contains magnetic minerals which align with
the poles
• When molten rock cools, a record of this is laid in the
rocks
Magnetic Reversals
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Keywords: Subduction
New crust is continuously
made. So why is the earth’s
crust not getting bigger?
Describe Wegner’s theory
of continental drift
Explain sea-floor
spreading and magnetic
reversals
Describe how new oceanic
lithosphere forms at midocean ridges
Keywords: Subduction
Subduction
• Occurs when oceanic crust collides with oceanic or continental crust
• The older, more dense, oceanic crust plunges back into the mantle at a
deep ocean trench.
• Forms deep ocean trenches & volcanic mountains or island arcs.
Trenches of the World
W
Section 3
Lesson Objectives
Describe the
three types of
plate boundaries
Describe the
three forces
that move the
plates and the
resulting stress
Explain how
scientists
measure the rate
of plate
movement
Describe the three types
of plate boundaries
Keywords:
Divergent boundary
Convergent boundaries
Transform boundaries
Ridge push
Convection
Slab pull
Stress
Tension
Compression
Shear
Describe the three
forces that move the
plates and the resulting
stress
Explain how scientists
measure the rate of plate
movement
Describe the three types
of plate boundaries
Describe the three
forces that move the
plates and the resulting
stress
Keywords: Divergent boundary
• Divergent
– plates move apart in
opposite directions
– Plate material is being
created
– Creates sea floor spreading
in oceanic crust
– Can also be continental crust
– East Africa Rift Valley is a
young divergent boundary
– The Red Sea is an older
divergent boundary that has
filled with water
Explain how scientists
measure the rate of plate
movement
Describe the three types
of plate boundaries
Describe the three
forces that move the
plates and the resulting
stress
Keywords: convergent boundary
• Convergent
– Plates collide together
– Plate material is being
destroyed
– Subduction and
mountain building takes
place due to convergent
boundaries
Explain how scientists
measure the rate of plate
movement
Plate Collisions
Oceanic Continental
Subduction
Oceanic Oceanic
Subduction
Continental–
Continental
(No Subduction
Mountain Range
instead)
Describe the three types
of plate boundaries
Describe the three
forces that move the
plates and the resulting
stress
Keywords: transform boundary
• Transform
– Plates slide past each
other
– San Andreas fault
Explain how scientists
measure the rate of plate
movement
Motion at Plate Boundaries
Plate Boundary Features
Describe the three types
of plate boundaries
Describe the three
forces that move the
plates
Explain how scientists
measure the rate of plate
movement
Keywords: ridge push, slab pull, convection
What causes the plates to move?
• Ridge push (occurs at mid-ocean ridges)
• Oceanic lithosphere is higher than where is sinks into
the asthenosphere so plate slides due to gravity
• Slab pull
• Parts of the Lithosphere sinks and pulls the rest of
faster as it sinks during subduction
• Convection
• Density differences
cause magma to rise
and fall carrying the
plates with it
Describe the three types
of plate boundaries
Describe the three
forces that move the
plates and the resulting
stress
Explain how scientists
measure the rate of plate
movement
Keywords: stress
• Tectonic stresses are those stresses produced by the
forces that drive plate tectonics
• Stress occurs at plate boundaries
• Stress = force per unit area
Types of stress at plate
boundaries
Tension: Stress that pulls apart
or stretches a body
Compression: Stress that
squeezes or shortens a body
Shear: Stress that pushes
parts in opposite directions
Dominant Stress at Boundary Types:
Divergent:
Tension
Convergent:
Compression
Transform:
Shear
To Do
• Complete Google Earth activity