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• Boundaries Draw-Along
• Plate Tectonics
Pg. 54
Pg. 55
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• Prior to Alfred Wegener’s theory of continental
drift geologists thought continents were fixed in
their locations. In developing his theory which of
the following evidence was NOT used by
Wegener?
a) Fossil similarities between southern continents.
b) Evidence of polarity change in found along the MidAtlantic Ridge.
c) Similarities in the paleoclimates of South America
and Africa.
d) The apparent fact the South America and Africa
seemed to fit together.
Plate Tectonics
Lithosphere - the rigid
outer layer of the Earth.
•Made of the crust
and the solid outer
layer of mantle.
Asthenosphere - the
layer of “plastic” rock in
the lower mantle.
• Flows like a very thick
liquid.
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Lithospheric Plates
• Lithospheric Plates-The
rigid lithosphere is
broken into plates
=tectonic plates
– Float on the semi
rigid, moving
asthenosphere.
Theory of Plate Tectonics – explains how the
lithospheric plates move and change shape.
Tectonic Plates
1. Earth’s lithosphere is broken into 7 major(large)
plates and numerous minor (smaller) ones.
2. The plates glide over the asthenosphere and
produce earthquakes, volcanoes and create
mountains.
Convection Currents
- driving forces of plate
tectonics - very hot
material at the deepest
part of the mantle rises,
then cools and sinks again,
then repeating.
This cycle is repeated over
and over.
HOT!!!!
***Remember…this heat is
generated by the core!!
How Plate Tectonic Works
As magma heats up and rises, it exits through the rift in the middle of the midocean ridge. It cools and pushes the plates apart.
The Asthenosphere is also moving in convection currents(created
by unequal heating), carrying the plates outward.
What is the average rate of movement
from lithospheric plates?
• 5cm/yr (2inches) and it is driven by unequal
heating of the Earth.
Plate Boundaries
1. Convergent – moving together
2. Divergent – moving apart
3. Transform – moving side by side