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Plate Tectonics
Continental Drift

Evidence for Continental Drift
A. Theory of continental drift is the idea that the
continents have moved horizontally to their
current locations.
1. This theory was developed by Alfred
Wegener.
2. Wegener believed
that all of the continents
were connected as one
large land mass (he
called Pangea) about
200 million years ago.
Alfred Wegener (1880-1930)
B. Fossils of Mesosaurs have been found in South
America and Africa.
C. Glacial deposits and grooved bedrock were
found in southern areas of South America,
Africa, India, and Australia.
D. Parts of the Appalachian mountains in the
eastern US are similar to those found in
Greenland and western Europe.
How Could the Continents
Drift?


Rock, Fossil and Climate clues were the main
evidence for continental drift during Wegener’s
lifetime.
Wegener’s theory was often rejected because no
one could explain how the continents moved.
Theory of Plate Tectonics

Plate Tectonics
A. Theory of Plate Tectonics is the idea that
the Earth’s crust and upper mantle are broken
into sections called plates that move around on
the mantle.
B. Composition of the Earth’s plates:
1. Lithosphere – the crust and part of the
upper mantle
2. Asthenosphere – the plastic-like layer
below the lithosphere
Plate Boundaries

There are three different plate boundaries:
Divergent Boundaries
Convergent Boundaries
Transform Boundaries
Divergent Boundaries

Divergent Boundaries are the boundaries
between two plates that are diverging, or
moving away from each other.
Convergent Boundaries


Convergent Boundaries are the boundaries
between two plates that are converging, or
moving towards each other.
There are three types of convergent
boundaries:
1. An ocean floor plate collides with a less dense
continental plate.
2. An ocean floor plate collides with another
ocean floor plate.
3. A continental plate collides with another
continental plate.
 Oceanic-Continental
Oceanic-Oceanic 
 Continental-Continental
Transform Fault Boundaries

Transform Boundaries are the boundaries
between two plates that are sliding
horizontally past one another.
Effects of Plate Tectonics

Landforms caused by plate tectonics:
a. rift valleys (divergent boundaries)
b. mountain ranges (continental-continental
convergent boundaries)
c. volcanoes (oceanic-continental
convergent boundaries)
d. faults (transform boundaries)
Causes of Plate Tectonics


Convection Current is the driving force of
plate tectonics in which hot, plastic-like
material from the mantle rises to the
lithosphere, moves horizontally, cools, and
sinks back to the mantle.
The convection currents provide enough
energy to move the plates in the lithosphere.
Quick Review of Plate Boundaries