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Plate Tectonics
6-1 Continental Drift
Continental
Drift
theory that the continents
were once a single land
mass that broke apart
Pangaea
supercontinent
Evidence of Continental Drift
South America
& Africa
look like they fit together
Fossils of mesosaurus
found in S. America &
Africa
Evidence of Continental Drift cont.
Mountains
on different
continents match
U.S.
& Canada match w/
Greenland & Europe
Sizes
of diamonds in
Brazil & W. Africa match
6-2 Seafloor Spreading
2
types of crust
Continental
○Less dense
Oceanic
○More dense
6-2 cont.
Mid-ocean
ridge
underwater mt.
chain in the oceans
Rift crack
Rift valley flat area
btw. ridges
6-2 cont.
New
seafloor
magma rises up through a
rift
Magma cools making new
crust
New crust pushes floor apart
at ridges
6-3 Evidence of Seafloor Spreading
Trench
deep canyons
in the ocean floor
Most
in the Pacific Ocean
Old
crust ends up in
trenches
Melts
again
& becomes magma
6-3 cont.
Subduction
zone area
where crust is forced down
in trenches
Youngest fossils = closest
to rift valleys, ridges, &
trenches
6-4 Plate Tectonics
Tectonic
plates the
lithosphere broken into
pieces
7
major plates & 8 minor
plates
Asthenosphere
part of the mantle
liquid
6-4 cont.
Theory
of Plate
Tectonics explains
how & why plates
(continents) move
Lithosphere floats on
asthenosphere
6-5 Plate Tectonics
Convection
current less
dense warm rises & denser
cool sinks
3 types of plate boundaries
Convergent
Divergent
Transform
6-5 cont.
Transform
2 plates
sliding past each other
Cause
earthquakes
6-5 cont.
Convergent 2 plates move
toward each other
○Oceanic + continental =
oceanic subducts under the
continental
○Continental + continental =
mountain
6-5 cont.
Divergent
2 plates move
away from each other
Cause rift valleys
Cause seafloor spreading
6-6 Effects of Plate Tectonics
Earthquakes
plates
slide past each other at a
fault
Mountains plates
collide & buckle upward
6-6 cont.
Volcanoes
oceanic plate
dips down & magma
collects
Hot
spots place where
magma reaches the surface
Islands
plates move over
hot spots & volcanoes build