Earth Science Review: Part 1
Pangaea
Alfred Wegener thought that the fit of the
freshwater and on land. How could fossils
of Mesosaurus be found so far apart? It’s
continents wasn’t just a coincidence. He
unlikely that it could have swum between
suggested that all the continents were
the continents. Wegener thought this
joined together at some point in the past.
reptile lived on both continents when they
In a 1912 lecture, he proposed the idea of
were joined as one giant landmass.
continental drift. According to the
Another fossil that helps support the
hypothesis of continental drift, continents
hypothesis of continental drift is
have moved slowly to their current
Glossopteris. This fossil fern has been
locations. Wegener suggested that all
found in Africa, Australia, India, South
continents were once connected as one
America, and most recently in Antarctica.
large landmass that broke apart about 200
The presence of this fern in so many
million years ago. He called this large
areas led Wegener to suggest that all of
landmass Pangaea, which means “all
these regions were once connected and had
land.”
a similar climate.
Long after Wegener’s death in 1930, his
basic hypothesis, that the continents have
Climate Clues
Glacial deposits and grooved bedrock
moved, was accepted. The evidence
found in South America, Africa, India, and
Wegener had to support his idea hadn’t
Australia show that these continents were
been enough to convince many people
once covered with glaciers. How could
during his lifetime. However, Wegener’s
you explain why glacial deposits were
early evidence has since been joined by
found in areas where no glaciers exist
other important observations. Let’s
today? Wegener thought that these
explore both Wegener’s clues and some
continents were all connected and covered
newer ones.
with ice near Earth’s south pole at one
Fossil Clues
time.
Besides the puzzle like fit of the
continents, other clues were found from
Glaciers
Glaciers are agents of erosion. As
fossils. Fossils of the reptile Mesosaurus
glaciers pass over land, they erode it,
have been found in South America and
changing its features. Glaciers then carry
Africa. This swimming reptile lived in
How could continents drift?
eroded material along and deposit it
Although Wegener provided evidence to
somewhere else. Glacial erosion and
support his hypothesis of continental drift,
deposition change large areas of Earth.
he couldn’t explain how, when, or why
Rock Clues
these changes had taken place. Because
If the continents were connected at one
other scientists at that time could not
time, then rocks that make up the
provide explanations either, Wegener’s
continents should be the same. Similar
idea of continental drift was rejected. The
rock structures are found on different
idea was so different that most people
continents. Parts of the Appalachian
closed their minds to it.
Mountains of the eastern United States are
Rock, fossil, and climate clues were the
similar to those found in Greenland and
main lines of evidence for continental drift.
western Europe. If you were to travel to
After Wegener’s death, more clues were
eastern South America and western Africa,
found and new ideas that supported
you would find rock structures that are
continental drift were discovered. One of
similar. Rock clues like these support the
these new ideas, seafloor spreading, helped
idea that the continents were once
provide an explanation of how the
connected.
continents could move.
Comprehension Questions
1. Define continental drift
2. Define Pangaea
3. What hypothesis suggests that continents have moved over time?
4. What did Wegener call the large landmass that broke apart to form the continents?
5. Fossils of what freshwater reptile found in both Africa and South America provided support
for continental drift?
6. State one reason why Wegener’s ideas about continental drift were not accepted?