continental drift - Madison County Schools

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Bellringer
Name seven different layers of Earth in
DECREASING order of DENSITY. Then name the
primary component(s) that make up each layer.
Drifting Continents
Notes
Continental Drift
• Some continents appear to be shaped
like puzzle pieces. For example the
west side of Africa and the east side of
South America look like matching
puzzle pieces.
Continental Drift
• Scientists Alfred Wegener tried to explain
why continents are shaped the way that they
are.
• Until the 1900s scientists thought that the
continents had always remained in the same
place.
• Even then it wouldn’t be until the 1970s until
the idea was firmly planted into mainstream
society.
Continental Drift
• Wegener thought that Earth had one big
continent about 300 million years ago. The big
continent broke into smaller pieces and formed
smaller continents. The continents slowly
drifted apart. Wegener called this continental
drift.
• According to Wegener, the continents has
drifted together to form the supercontinent
Pangea and a single superocean called
Panthalassa.
http://www.suu.edu/faculty/colberg/hazards/platetecton
ics/18_Pangaea.html
Continental Drift
•
•
•
Evidence shows that continental drift really happened.
Mountain ranges in Africa and South America as well as
North America and Africa line up as if they were once part
of the same mountain range.
At the time, most scientists believed that mountains
formed because Earth was still cooling and shrinking,
causing the surface to wrinkle like that of a dried-up apple.
Wegener claimed that if this were the case, then
mountains would be everywhere. He proposed that
because mountain ranges usually occur near continental
edges, then they formed when continents collided with
each other.
Formation of
the
Appalachian
Mountains
Matching
Mountain
Ranges
across S.
America and
Africa
Continental
Drift
• Wegener also used the existence of specific
fossils spanning multiple continents that are now
separated by vast oceans as evidence that the
continents were once connected.
• His primary fossil was Glossopteris, a fern-like
plant that lived 250 million years ago, and can
be found on Africa, S. America, Australia, India
and Antarctica.
• The existence of Mesosaurus and Lystrosaurs
across many continents also supported
Wegener’s hyposthesis.
Continental Drift
• Wegener also used evidence from climate
change to support his hypothesis. As a continent
moves away from the equator, its temperature
will drop. As a continent moves towards the
continent, its temperature will increase.
• Tropical plant fossils have been found in islands
above the Arctic Circle, meaning that at one time
that landmass was in a much warmer climate.
Continental Drift
• Large scratches in the bedrock of South America
prove that at one point in its history, S. America
was once much close to the south pole. These
scratches only appear where continental glaciers
once existed on top of the land.
• Currently both Greenland and Antarctica are
covered by continental glaciers. As the glaciers
melt in the summer months, they leave behind
large scratches or grooves in the rocks over which
they once covered.
Wegener’s Hypothesis
Rejected
•
•
•
•
Despite all of his evidence, Wegener could not explain
what causes continental drift. He saw that it did indeed
happen, but he couldn’t explain how or why.
His original idea had the continents plowing through
the ocean floor. (oops)
Because he did not have a fully developed idea, most
other scientists of his time thought that he was wrong.
More evidence would be required before Wegener’s
ideas would be accepted.
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