Transcript CONTINENTAL DRIFT

CONTINENTAL
DRIFT
Fact or Fiction?
You decide!!!!!!!!!!!!
Continental Drift
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Hypothesis that states that the continents once
formed a single landmass about 245 million
years ago, broke up, and drifted slowly to their
present day locations.
This hypothesis was presented by a German
meteorologist named Alfred Wegener in 1912.
Pangaea
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Mr. Wegener suggested that all of the continents
were joined together at some time in the past
like a big puzzle.
They were connected as one large landmass or
super continent known as Pangaea.
Pangaea means “all land” in Greek.
The giant ocean that formed was called
Panthalessa (“all sea”).
Pangaea later broke up in to 2 pieces: Laurasia
and Gondwana.
Why was his hypothesis so
CONTROVERSIAL?
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For scientists to believe a new theory or
idea, what do they want?
The evidence Wegener presented was not
enough to convince the other scientists.
Other scientists could not understand
what force could cause the crust to move
in this way.
Not until well after his death in 1930 was
his idea accepted.
What was his evidence?
CLUE #1—The Puzzle-like Fit
Wegener noticed that
many of the continents
fit together like puzzle
pieces.
Notice the outlines of
South America and
Africa.
What was the evidence?
CLUE #2---MESOSAURUS fossil
•The Mesosaurus was a swimming reptile
that lived in freshwater.
•Fossils of the Mesosaurus have been found
in South America and Africa.
•How could fossils of Mesosaurus be found
on land areas separated by a large ocean of
salt water?
•What do you think Wegener hypothesized?
What is the evidence?
CLUE #3—GLOSSOPTERIS fossil
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Plant fossil that has been found in Africa,
Australia, India, South America, and Antarctica.
The catch….it was a tropical plant.
Why would this be a clue?
What is the evidence?
CLUE #4---Climate
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Evidence of deposits from glaciers were
found in South America, Africa, India, and
Australia.
They also found rocks whose surfaces
were scoured and polished by glaciers.
What does this tell us about those
continents?
What is the evidence?
CLUE #5---Rocks
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If the continents were connected at one time,
then rocks that make up the continents should
be the same in locations where they were
joined.
Well…similar rock structures have been found on
different continents.
Parts of the Appalachian Mountains of the
eastern U.S. are similar to those found in
Greenland and western Europe.
Rocks in eastern South America and western
Africa are also similar.
What do scientists think now?
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The majority of scientists now believe in
Wegener’s idea.
They have established a concept known as
seafloor spreading that explains HOW the
continents moved.
Seafloor Spreading
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Seafloor spreading is the process by which
new oceanic crust forms as magma rises
toward the surface and solidifies.
Mid-ocean ridges are places where new seafloor is being created. They are underwater
mountain chains that run through the Earth’s
ocean basins.
As tectonic plates move away from each
other, the seafloor spreads apart and magma
fills in the gaps.
Where is the oldest seafloor? Where is the
youngest?