Chapter 9: Plate Tectonics
Review
Feb 11, 2013
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.
Convection
• Heated water is less dense therefore rises
while Cooled water is more dense, which
sinks.
• This is also true with air
Continental Drift
 Evidence of continental drift is the matching coastline shapes
of South America and Africa
 Also, South America and Africa where once joined because
 They fit together like a puzzle
 A mountain range lines up between Argentina and South
Africa.
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
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.
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
Sea-Floor Spreading
Molten material rises from the mantle and
erupts along the 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
Forming Mountains
• When 2 continental plates collide, folding
mountains occur
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.