Plate Tectonics
Chapter 8
8.1 What is Plate Tectonics?
Vocabulary:
Plate tectonics:
Continental Drift
Mid-ocean Ridge
Key Idea: The lithosphere is broken into rigid plates that move in
relationship to one another on the asthenosphere.
The lithosphere (geosphere) is the "solid" part of Earth.
It has two parts, the crust and the upper mantle.
(www.deafhoosiers.com/.../lithosphereComp.html)
URL: http://pubs.usgs.gov/gip/dynamic/dynamic.html use for
graphics
http://www.astro.virginia.edu/class/oconnell/astr121/im/usgs_asthe
nosphere.gif
This drawing shows the Earth's
lithosphere (crust and upper mantle)
on top of the asthenosphere.
Click on image for full size version
(40K GIF)
The crust is the upper layer of the
Earth. Under the oceans it is only
about 5 km thick while under the
continents it can be up to 65 km thick.
The plates that fit like puzzle pieces
around the Earth are made of Earth’s
crust and the upper part of the mantle layer. Together the crust and
upper mantle are called the lithosphere and they extend about 80
km deep.
These plates move a little bit each year as they slide on top of a layer in
the mantle called the asthenosphere. This layer can be pushed and
deformed like silly putty, flowing because of the warmth of the Earth.
The flowing asthenosphere carries the lithosphere including the
continents, plants, animals and you on its back.
Crust, the upper layer of the Earth, is not always the same. Crust
under the oceans, called oceanic crust, is much thinner than
continental crust. It is only about 5 km thick while continental crust
can be up to 65 km thick. Also, the two types of crust are not made of
the same materials. Oceanic crust is made of a denser collection of
minerals than continental crust.
The tectonic plates are made up of the Earth’s crust and the upper
part of the mantle layer underneath. Together the crust and upper
mantle are called the lithosphere and they extend about 80 km
deep. The lithosphere is broken into giant plates that fit around the
globe like puzzle pieces. These puzzle pieces move a little bit each
year as they slide on top of a somewhat fluid part of the mantle called
the asthenosphere.
The asthenosphere is solid even though it is at very hot
temperatures of about 1600 C due to the high pressures from above.
However, at this temperature, minerals are almost ready to melt and
they become ductile and can be pushed and deformed like silly putty
in response to the warmth of the Earth. These rocks actually flow,
moving in response to the stresses placed upon them by the churning
motions of the deep interior of the Earth. The flowing asthenosphere
carries the lithosphere of the Earth, including the continents, on its
back.
Hypothesis or Theory
Continental Drift Theory
Supporting Evidence
Similarities in the shapes of the
continents (look at the west
coast of South America and the
East Coast of Africa); same
fossils and rock formations
found in South America and
Africa; climate change evidence
Theory of Plate Tectonics
Location of earthquakes and
volcanoes; magnetism of ocean
floor; age of ocean floor.
Alfred Wegener proposed the Continental Drift Theory. His theory
took many years to be accepted. Scientists conducted studies of fossils,
rocks, plant life and land formations which helped support Wegener’s
theory.
8.2 Types of Pate Boundaries
Vocabulary:
Divergent boundary
Rift valley
Rift
Convergent boundary
Subduction boundary
Deep-sea trench
Collision boundary
Transform boundary
RIFT VALLEY
MID OCEAN RIDGE AND RIFT VALLEY
DIVERGENT BOUNDARY
Different Boundary types
Rift Valley
Collison Boundaries 
Key Idea: Boundaries between plates are described generally
as divergent, convergent, or transform, depending on how the
plates move relative to each other.
Subduction Boundaries
 Two plates converge 
Two Oceanic Plates
Oceanic and Continental Plate


One Plate Subducts beneath
Oceanic plate subducts
the other
beneath continental plate


Deep Sea Trench forms
Deep-sea trench forms in the
between two plates
ocean


Volcanic island arc/chain of
Mountain chain and volcanoes
volcanic islands form on the
form on land
overriding plate
Divergent Boundary

Two Plates Move Apart

Molten rock forces its way upward through cracks/rifts

Molten Rock cools

Older oceanic crust moves away from the mid ocean ridge
8.3 Causes of Plate Movement
Vocabulary
Mantle convection: A process by which heat from Earth’s
inner and outer cores is transferred through the mantle.
Ridge push: A force that is exerted by cooling, subsiding rock
on the spreading lithospheric plates at a mid-ocean ridge.
Slab pull: A force at a subduction boundary that the sinking
edge of the subducting plate exerts on the rest of the plate.
Need to Know: The lithosphere is rigid and brittle which
means that it breaks apart. The asthenosphere, below the
lithosphere is not rigid but pliable or flexible. Instead of
breaking, things bend. This is important to remember when
we study chapter 11!
Cause of Plate Movement
1. Mantle Convection
2. Slab Pull
3. Ridge Push
Type of Boundary
Divergent boundary

Divergent boundary

Subduction boundary
8.4 Plate Movement and Continental Growth
Vocabulary
Pangea: The name of a hypothetical landmass consisting of
all the continents welded together, which evidence indicates
existed about 250 million years ago.
Craton: The ancient core of a continent, which is tectonically
stable.
Terrane: A large block of lithospheric plate that has been
moved, often over a distance of thousands of kilometers, and
attached to the edge of a continent.
Key Idea: Plate movements have caused Earth’s continents to
change their positions on the globe over time. New material
has been added to the continents as a result of plate tectonics.
Evidence of Earth’s Past:
1.
2.
3.
4.
Mountain ranges far from plate boundaries today
Data about the ages of rocks
Fossils
Evidence of glaciers in lands that are now tropical
Sources of Growth Material:
1.
2.
3.
4.
Deep-sea sediment
Igneous rock
River sediment
Terranes
PANGEA
Terrane: A large block of lithopheric plate that has been
moved, often over a distance of thousands of kilometers, and
attached to the edge of a continent.
CRATON: The ancient core of a continent which is tectonically
stable