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Lesson 7-3
The Theory of Plate Tectonics
The Plate Tectonics
Theory
The theory of plate tectonics states that Earth’s
surface is made of rigid slabs of rock, or
plates, that move with respect to each other.
The word tectonic describes the forces
that shape Earth’s surface and rock
structures that form as a result.
The Pacific Plate is the largest of the tectonic
plates
Earth’s Structure
Earth’s crust and upper mental
make up the lithosphere.
These layers are cold,
rigid rock.
Below the lithosphere is the
asthenosphere.
This layer is hot and
flows like plastic
(meaning that it can be
molded or change shape
without breaking)
-
Plates on the
lithosphere move
because they rest on
the flowing
asthenosphere.
Plate Boundaries
Plate Boundary: where two plates meet.
Divergent Plate
Boundaries
A Divergent Plate Boundary
is when two plates move
away from each other.
In the ocean, mid-ocean
ridges are located at
divergent plate boundaries.
On a continent a divergent
plates cause rift valleys to
form.
Transform Plate
Boundaries
When two plates slide
by each other, a(n)
transform plate
boundary forms.
This type of
movement cause
earthquakes.
Convergent Plate
Boundaries
When two plates
collide, a convergent
plate boundary forms.
When the denser plate
slides under the lessdense plate during
the collision,
subduction occurs.
Convergent
Plate Boundaries
When oceanic and
continental plates collide a
deep ocean trench forms
with volcanos nearby.
Ex. Mount Rainier
When two oceanic plates
collide, a trench forms.
When two continental plates
collide, mountains form
Ex: The Himalayas
Evidence of
Tectonic Plates
Today, scientists use satellites to
measure how fast the continents
move.
By using the theory of plate
tectonics, scientists can explain why
earthquakes and volcanoes occur in
certain locations.
Plate Motion
The asthenosphere moving underneath the
lithosphere causes the continents to move.
Convection currents cause tectonic plates to
move.
Convection is the circulation of
material caused by differences in
temperature and density.
Convection currents form in the mantle when thermal
energy transfers from the core to the mantle.
Forces Causing
Plate Motion
Three forces interact to cause tectonic plate motion.
Convection currents in the mantle produce a
force that cause motion called basal drag.
The force of ridge push causes the plates to
be pushed away from each other at mid ocean
ridges.
When a plate sinks below another plate, it
pulls on the rest of the plate, exerting a force
called slab pull.
A Theory in Progress
Plate tectonics is the unifying theory of geology.
It explains the connections between
continental drift and the formation and
destructions of Earth’s crust along plate
boundaries
It also explains the occurrence of
earthquakes, volcanos, and mountains.
Scientists still have several unanswered
questions.