Transcript Internal Structure of the Earth

Plate Tectonics
Theory of Continental Drift
• The theory that
continents drifted
across the ocean to
get their current
spots on the globe.
• First suggested by
Alfred Wegner
• First used the idea of
one super giant
continent called
Pangaea.
What was the evidence behind
Wegner’s idea?
• The continents fit together like puzzle
pieces.
• The fossils and rocks on separate
continents being identical.
• Climate regions (found by looking at
fossils) that did not match up with the
positions the continents are located today.
Theory of Seafloor Spreading
• Molten material rises at
the Mid-Ocean Ridge.
• The material flows away
from the ridge, carrying
the land that was once
together, further apart.
Theory of PLATE TECTONICS
• First accepted in 1968 by a man named
Hess.
• Combined the ideas of seafloor spreading
and continental drift.
• States that the Earth’s crust and upper
mantle are broken into sections called
plates.
• Animation
Why do the plates move?
• Hot magma from within the Earth rises to
the surface then cools down and sinks
back into the Earth. (convection)
Convection Currents
This is what powers the movement
of the continents
Graphic
What makes the plates move?
1. New seafloor is
created and
spreads out.
2. The continents
on either side
begin to move
away from each
other.
What makes the plates move?
3. Dense seafloor
hits continental
land.
4. Denser floor goes
into the mantle and
melts.
How do the plates move?
The plates move in three different ways:
Collide
Separate
Slide past each other
Convergent Plates
Continent vs. Ocean
• The more dense ocean
plate slides under the less
dense continental plate
(Subduction)
• Chains of volcanoes are
formed along the edge of
continents. Also trenches
are formed off the coast of
the continent.
• The Cascade Mountain
chain is formed this way.
Convergent Plates
Ocean vs. Ocean
• Both dense plates are
pushed towards the
center of the Earth
• Extremely deep trenches
are formed, and also
chains of volcanic
islands are created
(island arcs)
• The Japanese Islands
are formed this way.
Convergent Plates
Continent vs. Continent
• When two continental plates
hit both plates are forced
up. No subduction occurs.
• Mountains are formed, not
volcanoes.
• The Himalayan Mountains
in India are formed this way.
Transform Boundary
• When one plate slides
past another.
• The most famous is
the San Andreas fault
in California.
• No creation of
anything, just
destruction.
Divergent Boundary
• When two plates
separate from each
other.
• The Mid-Atlantic ridge
is the best example.
• This is what caused
Europe and the
United States to
separate.
Animation