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Continental Drift
Continental Drift
• Some continents look like
they fit like puzzle pieces
• Ex. South America and
Africa
• Alfred Wegner proposed
theory of continental drift.
• Continental drift,
continents have moved
slowly to their current
locations.
Pangaea
• Wegener proposed,
200 million years ago,
the continents were
one landmass.
• He called the
landmass Pangaea.
• Pangaea meaning “all
land”
• Wegener’s theory was
highly controversial, due
to his lack of proof.
• He proposed that
continents plowed
through the ocean floor
because of the spin of the
earth.
• It wasn’t until the 1930’s
and after his death that
his hypothesis was
accepted, due to
advancements in
technology.
Fossil Clues
• Fossil gave support to
Wegner’s idea.
• Fossils of the reptile
Mesosaurus have been
found in South America and
Africa.
• Another fossil that supports
the hypothesis of
continental drift is
Glossopteris. found in
Africa, Australia, India,
South America, and
Antarctica.
Climate Clues
• Fossils of warmweather plants were
found on the island of
Spitsbergen in the
Arctic Ocean.
• Wegner hypothesized
it drifted from a
tropical region.
Rock Clues
• Similar rock
structures found on
different continents.
• Appalachian
Mountains similar to
those found in
Greenland and
Western Europe.
• Wegner, could not explain, when, why, or how.
• Move to How the Earth was made film
Seafloor Spreading
• Sound waves used to
measure depth of
ocean floor
• Method used during
World War II, and
rifts, valley, and
mountains were
found.
• Looked similar to
continents
• In rift valleys, volcanic
eruptions and
earthquakes
discovered.
• Ridges called midocean ridges
• Harry Hess came up
w/ Seafloor Spreading
Theory.
• Hot, less dense material
rises toward the surface
at the mid-ocean ridges.
• Then flows sideways,
carrying the seafloor
away from the ridge in
both directions.
• This creates new
seafloor.
• New seafloor closer to
ridge
• Older seafloor moves
away from ridge
Magnetic Clues
• http://www.youtube.com/watch?v=GyMLlL
xbfa4&feature=related
• Magnetic poles will reverse themselves.
South becomes North and North becomes
South.
• Rock samples along the ridge
demonstrate this change in polarity over
time.
• Parallel line of rock,
demonstrates normal
and reverse polarity
on each side of the
ridge.
• http://www.youtube.co
m/watch?v=BCzCmldi
aWQ
__________ is the hypothesis that
continents have slowly moved to their
current locations.
• A. Continental drift
• B. Mid-ocean shifting
• C. Pangaea
• D. Seafloor spreading
Who proposed the hypothesis of continental
drift?
• A. Esker
• B. Gagarin
• C. Hess
• D. Wegener
• What is Pangea?
• Pangaea means “all land” and is the name
that Wegener used to refer to the one
large landmass that he believed existed
before it broke apart into continents.
• What is seafloor spreading?
• Seafloor spreading is the process in which
hot, less dense material below Earth’s
crust rises toward the surface at the midocean ridges. This material flows sideways
and carries the seafloor away from the
ridge in both directions.
• How did scientists realize that the ocean
floor was not flat, and what did they
discover?
• During WWII, the military used sonar to
look for submarines. What they found
were different depths, which when
compiled, showed, canyons and
mountains like that on earth.