Transcript Plate Tectonics 2006

PLATE TECTONICS
Alfred Wegener
1912, German scientist.
 Proposed a hypothesis called “continental
drift.”
 “Supercontinent” broke up into smaller
continents.

Evidence for “Continental Drift”
Fossils
 Rock Formations
 Climate


What Wegener couldn’t figure out is
“How?”
Harry Hess
1950’s hypothesis- “Sea-Floor Spreading”
 Was the missing link for Wegener’s
hypothesis.
 1960’s – “Paleomagnetism”


By the end of the 1960’s…all the data and
hypothesis’s were merged to develop the
theory of “Plate Tectonics.”
Plate Tectonics

How and why continents move and the
study of the formation of features in the
Earth’s crust.
How Continents Move…
Lithosphere- crust
and rigid upper part
of the mantle.
 Asthenosphere‘plastic’ layer below
the lithosphere.
Flows like putty!

Two Types of Crust

Continental Crust
– Made primarily from silica.
– Less dense than oceanic crust.

Oceanic Crust
– Made primarily from iron and magnesium.
– More dense than continental crust.

What do these densities mean?
The Major Plates
1.
2.
3.
4.
5.
6.
7.
8.
North American
South American
Nazca
Pacific
Antartic
African
Eurasian
Indo-Australian
TYPES OF PLATE BOUNDARIES
1.
DIVERGENT
2.
CONVERGENT
3.
TRANSFORM
Divergent Plate Boundaries

What does it mean to
diverge?
– Plates move apart

2 Types:
a) Ocean – Ocean
b) Continent – Continent

Predict what would
happen as a result of
a) Ocean-ocean
divergent motion
b) Continent-continent
divergent motion
Ocean – Ocean Divergent
Boundaries

Sea floor spreading
creates a Mid-Oceanic
Ridge.
– Basalt
– Undersea volcanoes
Continent – Continent Divergent
Boundaries

Hot magma rises and
causes the crust to split.

Causes the land to drop
and form a deep valley.
– Rift valley

As spreading continues,
the rift valley will
lengthen, deepen, and
make a sea.
– Red Sea
Africa’s Rift
Valley & The
Red Sea
Convergent Plate Boundaries


What does it mean to
converge?
– Plates are moving
together.
3 Types:
1. Ocean – Ocean
2. Continent – Continent
3. Ocean - Continent

Based on the model below
– Make some observations
about what happens at
convergent plate
boundaries
– Predict what would
happen at these
boundaries
Ocean – Ocean Convergent
Boundaries
One oceanic crust dips below the
other – subduction.
 Forms an ocean trench.
 Examples include volcanic island
arcs such as Japan and the
Caribbean.

Ocean – Continent Convergent
Boundaries
Denser oceanic crust
subducts below
continental crust.
 Causes mountains
with volcanic activity
 Examples—Cascade
Mts. in Washington,
Oregon, and
California & Andes
Mountains.

Continent – Continent
Convergent Boundries


Continents will smash
together, NO
SUBDUCTION,
making mountain
ranges.
Examples include the
Himalayas.
TRANSFORM BOUNDARIES
Plates are sliding past each other.
 Examples include the San Andres Fault in
California.

Transform Boundaries
Occurs when two
plates slide past
each other.
 Examples include
the San Andres
Fault in
California.

SAN
ANDREAS
ALPINE FAULT
BOUNDARY IN
NEW ZEALAND
How is plate motion happening?
Scientist’s aren’t really sure!
 They believe ‘convection’ is the main reason.

-Convection is the movement of heated material
due to differences in density caused by
differences in temperature.
The Earth is a convection system!
Heat (energy) comes from radioactive elements
within the Earth’s core.