Table of Contents
Chapter 7: Plate Tectonics
Section 1. Continental Drift
Continental Drift
Evidence for Continental Drift
• If you look at a map of Earth’s surface, you
can see that the edges of some continents
look as though they could fit together like a
puzzle.
Continental Drift
A. Pangaea
1. German meteorologist Alfred Wegener (VEG
nur) proposed the hypothesis of continental
drift in 1912.
2. According to the Wegener’s hypothesis of
continental drift, continents have moved
slowly to their current locations.
Continental Drift
A. Pangaea
3. Wegener suggested that all continents once
were connected as one landmass that broke
apart about 200 million years ago.
4. He called
this large
landmass
Pangaea (pan
JEE uh),
which means
“all land.”
Continental Drift
B. A Controversial Idea
1. Wegener’s
hypothesis on
continental drift was
controversial idea.
He did not have
enough evidence.
Click image to view movie.
Continental Drift
B. A Controversial Idea
2. Wegener proposed that the continents plowed
through the ocean floor, driven by the spin of
Earth.
3. Physicists and geologists of the time pointed
out that continental drift would not be necessary
to explain many of Wegener’s observations.
4. It wasn’t until long after Wegener’s death in
1930 that his basic hypothesis was accepted.
Continental Drift
C. Fossil Clues
1. Fossils are the remains, imprints, or traces of
prehistoric organisms. They can tell when
and where organisms once lived and how they
lived.
2. Animal fossils offer one clue that the
continents might have been joined together
millions of years ago.
Continental Drift
C. Fossil Clues
3. For example,
fossils of the
reptile
Mesosaurus
have been
found in South
America and
Africa.
Continental Drift
C. Fossil Clues
4. This swimming reptile lived in freshwater
and on land.
5. How could fossils of Mesosaurus be
found on land areas separated by a large
ocean of salt water?
6. Wegener hypothesized that this reptile
lived on both continents when they were
joined.
Continental Drift
D. A Widespread Plant
1. Another fossil that supports the hypothesis
of continental drift is Glossopteris (glahs
AHP tur us).
2. This fossil plant has been found in Africa,
Australia, India, South America, and
Antarctica.
Continental Drift
D. A Widespread Plant
3. The presence of Glossopteris in so many
area also supported Wegener’s idea that all
of these regions once were connected and
had similar climates.
Continental Drift
E. Climate Clues
1. Scientists have found fossils of warmweather plants on the island of Spitsbergen
in the Arctic Ocean. This is one of the
coldest place on Earth.
2.To explain this, Wegener’s hypothesis of
continental drift proposed that Spitsbergen
Island drifted from tropical regions to the
arctic.
Continental Drift
F. Rock Clues
1. Glaciers are large, slow moving bodies of
ice on land.
2. Glacial deposits and rock surfaces scoured
and polished by glaciers are found in South
America, Africa, India, and Australia.
3. This shows that parts of these continents
were covered with glaciers in the past.
Continental Drift
F. Rock Clues
4. Similar rock structures are
found on different
continents.
5. For example, parts of the
Appalachian Mountains of the
eastern United States are
similar to those found in
Greenland and western Europe.
6. Rock clues like these support the idea that the
continents were connected in the past.
Continental Drift
G. How could continents drift?
1. Although Wegener provided evidence to
support his hypothesis of continental drift,
he couldn’t explain how, when, or why
these changes took place.
Continental Drift
G. How could continents drift?
2. Because other scientists could not provide
explanations either, Wegener’s idea of
continental drift was initially rejected.
3. After Wegener’s death, new technology
provided new evidence. New ideas about
continental drift were developed. One of
these ideas is called seafloor spreading.
You’ll learn more about this in the next
section.
Section Check
Question 1
__________ is the hypothesis that continents
have slowly moved to their current locations.
A. Continental drift
B. Mid-ocean shifting
C. Pangaea
D. Seafloor spreading
Section Check
1
Question 2
Who proposed the hypothesis of continental
drift?
A. Esker
B. Gagarin
C. Hess
D. Wegener
Section Check
1
Question 3
What is Pangaea?
End of Chapter Summary File