Download Chapter 9: Plate Tectonics Review

Chapter 9: Plate Tectonics
Review
Feb 11, 2013
What to study?
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Layers of the Earth
Convection Currents
Continental Drift
Sea-floor Spreading
Theory of Plate Tectonics
Plate Boundaries
Crustal Features
Shadow Zone
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– Study Plate Tectonics 8.9A and 8.9B
Layers of the Earth
From the Earth’s Crust to the Inner Core:
Depth Increases
Pressure Increases
Temperature Increases
Layers of the
Earth
Crust
Temp.
(°C)
0- 860 °C
Mantle
870°C
Outer
Core
2200°C
Inner
Core
5000°C
Lithosphere
• This layer is broken down into several large
tectonic plates
Asthenosphere
• The asthenosphere is the semirigid part of the middle mantle
that flows like hot asphalt
under a heavy weight.
• The tectonic plates float on
this semi-liquid layer.
Lithosphere Vs. Asthenosphere
Lithosphere= rigid
Asthenosphere= semi-soft
Convection Currents in the Mantle
• According to scientists, convection currents is
the driving force behind the movement of the
Earth’s plates.
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Convection
• Heated water is less dense therefore rises
while Cooled water is more dense, which
sinks.
• This is also true with air
Alfred Wegener’s hypothesis on
Continental Drift
All the continents had once been
joined in a single landmass,
called Pangaea, and have since
drifted apart.
• Evidence from Landform
• Evidence from Fossils
• Evidence from Climate
Evidence of Continental Drift
 A mountain range lines up between Argentina in South America and
Africa.
 Fossils of the reptiles Mesosaurus and Lystrosaurus have been found in
places now separated by oceans.
 Fossils of the fernlike plant, Glossopteris, have been found in rocks in
Africa, South America, Australia, India, & Antarctica.
 Deep scratches in rocks show that continental glaciers once covered South
Africa.
Continental Coastlines
Why don’t the continents look like they did millions of years ago?
• Coastlines change over time due to beach erosion.
Pangaea
• A supercontinent, meaning “all lands”, that
existed about 300 million years ago.
Scientists Reject Wegener’s Hypothesis
• Wegener could not provide a satisfactory
explanation for the force that pushes or pull
the continents.
Sea-Floor Spreading
Molten material rises from the mantle and
erupts along the mid-ocean ridge
Mid-Ocean Ridge
Subduction
• Process by which the ocean floor sinks
beneath a deep-ocean trench and back into
the mantle.
Plate Tectonics
• Geological theory that states that pieces of
Earth's lithosphere are in constant, slow
motion
Earthquakes
• Occur usually when 2 plates slide past each
other, however, can happen at all plate
boundaries.
• Release of energy when the lithosphere
suddenly breaks and slides
Convergent Boundaries
• Two plates collide
• Example: Himalayan Mountains
• Folding mountains, volcanoes, and trenches
can form as a result of plates colliding.
Divergent Boundaries
• Plate boundary where 2 plates move away
from each other.
• Is the result of new ocean floor, such as the
mid-ocean ridge and valley’s on land.
Transform Boundaries
• Plate boundary where two plates slip past
each other, moving in opposite directions.
• Earthquakes frequently occur along these
boundaries.
Cause of Deep Ocean Trenches
• When an ocean plate collides with a
continental plate, the plate is subducted
under the continent.
Ring of Fire
Volcanoes form where tectonic plates meet
other plates.
Seismic Waves (PreAP)
• Scientists use the properties of waves to study the
internal structure of Earth. Seismic waves are sound
waves that may be generated by earthquakes.
• Primary waves, also known as P-waves, are
longitudinal waves and can travel through both solids
and liquids.
• Secondary waves, also called S-waves, are transverse
waves that only travel through solids.
• As these waves pass through the interior of Earth,
they change speed or may become refracted or
reflected.
Shadow Zone
• A wave-free shadow zone exists because the waves are
refracted from their original path as they pass through the
boundary between the mantle and the core where they
experience changes in density.
Earthquake Epicenter
P- and S- Waves
P- and S- Waves
103 º
103 º
shadow zone
shadow zone
143º
143º
P-Waves only