Transcript Plate Tectonics _2010

Why does Earth have mountains?
 Where do they come from?
 Why are there ocean fossils at the top
of the Himalayas?
 Why does California have
Earthquakes?
 Where do volcanoes come from?

Plate Tectonics
Chapter 8
Alfred Wegener

Continental Drift


Wegener thought whole
sections of the crust moved
Evidence


Shape of Continents
Glacier Evidence


Rock Evidence


Glacial till in tropics
Same mountains on different
continents
Fossil Evidence

Same fossils on different
continents
Continental Drift
Africa and South America
look like they fit
together

1.
2.
3.
Click on the picture to
see the evidence
Ancient Mountain Belts
Ancient Sand Dunes
Fossil Evidence
Continental Drift
Fossil Evidence
- Same fossils found on
different continents
1.
2.
3.
4.
Mesosaurus
Lystrosaurus
Glossopteris
Cynognathus
Continental Drift

What the hypothesis was missing was the
HOW?


Alfred Wegener proposed that the
continents were moving on a more fluid
layer under the crust that could possibly be
moving due to internal heat . . .
He had no way to prove it!
He was right!. . .well mostly


He died before his hypothesis was
accepted as a theory.
New technology allowed scientists to
examine the structure of Earth


They found that the lithosphere was moving
due to Earth’s internal heat.
This developed into the theory of Plate
Tectonics
Who came up with continental drift?
1.
2.
3.
4.
Alfred Wegener
Sir Isaac Newton
Copernicus
Alfred Hitchcock
0%
1
0%
0%
2
3
0%
4
What evidence did Alfred Wegener
use to support continental drift?
1.
2.
3.
4.
Shape of
continents
Rock evidence
Fossil evidence
All of the above
0%
1
0%
0%
2
3
0%
4
Why could Alfred Wegener not
prove continental drift?
1.
2.
3.
He could not
prove the land
moved
He could not
prove how the
land moved
He did
0%
1
0%
2
0%
3
Where do most earthquakes and
volcanoes occur?
1.
2.
3.
4.
In the middle of
plates
Along coasts
Along mountain
ranges
Along plate
boundaries
0%
1
0%
0%
2
3
0%
4
Plate Tectonics

Evidence


Continental Drift (continents fit, fossils, rocks)
New Evidence
Location of Earthquakes and Volcanoes
(p173)
 Magnetism of the ocean floor (p174)
 Age of the ocean floor (p175)

Plate Tectonics Evidence
Earthquakes and Volcanoes:

Most earthquake and volcano activity happen
along plate boundaries.

Plates are moving apart, moving together, or
sliding past one another.


This creates earthquakes
Where plates move apart and come together
magma is brought to the surface

This creates volcanoes
Plate Tectonics
World Earthquakes
See page 262 to view direction of
plate movement
Plate Tectonics Evidence
Magnetism of the Ocean Floor




(see page 258)
Mid-ocean Ridges are places where NEW rock
is forming.
These rocks contain magnetic minerals
(minerals with iron) they point to the north
pole
The north pole can flip with the south pole
These minerals flip too. This is called a
magnetic reversal.
Plate Tectonics
Seafloor Magnetism
Video
Plate Tectonics Evidence

Age of the Ocean Floor

New rock is formed at a mid-ocean ridge or
spreading center


These are formed in the middle of the ocean
The rock gets older as you move away from
the ridge
The ocean floor is not that old because it subducts
under continents
 The oldest ocean floor is ~180 million years old

Plate Tectonics
oldest
Age of the ocean floor
youngest
Earth’s Structure





Crust + Upper Mantle
= Lithosphere (solid)
Asthenosphere “fluid”
portion of the mantle
Mantle - Solid
Outer Core – Liquid
Inner Core – Solid

Heat comes from
radioactive material in
the core
Mantle Convection
Composition
Thick
Thin
High Density
Low Silica
Sinks
Low Density
High Silica
Floats
3 Types of Plate Boundaries:
1.
Divergent
2.
Convergent
3.
Transform
Divergent Boundary
Sea floor spreading
 Large continents
begin to crack and
split apart
 The gaps fill with
water
 Small seas become
oceans
 The mid ocean
ridge continues to
produce new crust
Divergent Boundary
Characteristics



2 plates are moving apart
Shallow Earthquakes
Magma comes to the surface and cools

Basalt rock forms


Creates a Mid-Ocean Ridge


Dense and dark in color
Rift valleys form in the center
Examples: Mid Atlantic Ridge and East
Pacific Rise
Divergent Boundary
How?



The plates are pulled
apart by convection
currents in the mantle
below
Caused by heat released
from natural radioactive
processes
At mid-ocean ridges
molten rock from below
rises up to fill the gap
with new basaltic rock
Let’s Draw a Divergent Boundary
Using the Map on page 262 Highlight the
Divergent Boundaries
True or False: The magnetic
polarity of Earth changes
1.
2.
True
False
0%
1
0%
2
Magnetic stripes of oceanic crust proves…
1.
2.
3.
Earth is rotating
One piece of
evidence to prove
plate movement
That the rocks are
very old
0%
1
0%
2
0%
3
Seafloor rock gets older as…
1.
2.
3.
You move away from
the mid-ocean ridge
As you move toward
the mid-ocean ridge
As you move into
the mid-ocean ridge
0%
1
0%
2
0%
3
The Lithosphere is…
1.
2.
3.
4.
The crust and the
upper mantle
Another word for
mantle
The crust and
asthenosphere
The inner core
0%
1
0%
0%
2
3
0%
4
Which layers of the Earth are solid?
1.
2.
3.
4.
5.
6.
Inner Core
Outer Core
Mantle
Crust
All of the above
1, 3, and 4
0%
1
0%
0%
0%
2
3
4
0%
0%
5
6
Which layers of the Earth are
liquid?
1.
2.
3.
4.
5.
6.
7.
Inner core
Outer core
Mantle
Asthenosphere
Crust
All of the above
2 and 4
0%
0%
0%
0%
0%
0%
0%
1
2
3
4
5
6
7
A divergent boundary is where
plates…
1.
2.
3.
Move apart
Come together
Slide past each
other
0%
1
0%
2
0%
3
All divergent boundaries eventually
form…
1.
2.
3.
4.
Mountains
Oceans
Continents
The moon
0%
1
0%
0%
2
3
0%
4
3 Types of Plate Boundaries:
1.
Divergent
2.
Convergent
3.
Transform
Convergent Boundaries

2 plates are moving together
Ocean-Ocean
 Ocean-Continent
**Deep Earthquakes

Subduction Zone
Volcanoes Form
Creates Mountain Belts
Continent-Continent
**Earthquakes

NO VOLCANOES
Convergent Plate Boundaries
• Where lithospheric plates are moving towards one another at
their boundary, lithospheric area must be consumed. This is
accomplished by subduction or thickening and delamination.
32
Convergent Boundaries
-Subduction

Ocean-Ocean or Ocean-Continent
The denser plate always subducts
Volcano Forms
•Subducting Plate
• more dense
Plate Melts
Ocean – Continent Subduction
Ocean – Continent Subduction



The ocean plate always subducts because
it is more dense.
Continental volcanic arcs or a mountain
chain of volcanoes form on the continental
plate.
Examples: Cascades of N. America
Andes of S. America
Ocean – Ocean Subduction
Ocean – Ocean Subduction



The denser ocean plate always subducts
because it is more dense.
Volcanic island arcs or chains of volcanic
islands form on the OTHER OCEAN plate.
Examples: Aleutian Islands, Alaska
Mt Pinatubo, Philippines
Mt Fuji, Japan
Lets Draw a Subduction
Boundary
Collision Boundary
Collision Boundary
Convergence of India
Collision Boundary



There is NO SUBDUCTION because both
plates are continental and have low
density.
They buckle up forming mountains (not
volcanoes)
Examples: Himalayas, India/Asia
Highlight and Label the Major
Convergent Boundaries
Using the Map on page 712-713 Highlight the
Divergent Boundaries
What tectonic plate ALWAYS
subducts?
1.
2.
3.
4.
Oceanic plate
Continental plate
Both
Neither
0%
1
0%
0%
2
3
0%
4
What convergent boundary can
form volcanoes?
1.
2.
3.
4.
5.
6.
Ocean – ocean
Ocean – continent
Continent –
continent
All of the above
1 and 2
3 and 4
0%
1
0%
0%
0%
2
3
4
0%
0%
5
6
What is an example of a
continental volcanic arc?
1.
2.
3.
4.
5.
6.
Hawaii
Cascades
Himalayas
Andes
2 and 4
All of the above
0%
1
0%
0%
0%
2
3
4
0%
0%
5
6
What is an example of a volcanic
island arc?
1.
2.
3.
4.
5.
6.
7.
Hawaii
Mt. Pinatubo
Cascades
Himalayas
Mt. Fuji
2 and 5
All of the above
0%
0%
0%
0%
0%
0%
0%
1
2
3
4
5
6
7
What plate subducts in a collision
boundary?
1.
2.
3.
The more dense
continental plate
Both continental
plates
Neither
continental plate
0%
1
0%
2
0%
3
What is an example of a collision
boundary mountain range?
1.
2.
3.
4.
5.
6.
7.
Hawaii
Mt. Pinatubo
Cascades
Himalayas
Mt. Fuji
1, 2, and 4
All of the above
0%
0%
0%
0%
0%
0%
0%
1
2
3
4
5
6
7
3 Types of Plate Boundaries:
1.
Divergent
2.
Convergent
3.
Transform
Transform Boundaries

Occur when 2 plates are sliding past one
another
** Earthquakes!


Ocean – Ocean
Ocean – Continent
Continent - Continent
No Volcanic Activity
Examples


San Andreas Fault
Along Ocean Floor
Let’s Draw a Transform
Boundary
Highlight and Label the Major
Transform Boundaries
Using the Map on page 712-713 Highlight the
Transform Boundaries