The continental drift hypothesis, proposed by Alfred Wegener, suggests that all continents were once part of a supercontinent called Pangaea and have since moved to their current positions. Evidence supporting this hypothesis includes the fitting shapes of continents, fossil correlations, and similarities in mountain ranges across different continents. Despite initial skepticism, Wegener's ideas gained acceptance decades later, particularly after the discovery of plate tectonics.

1. The Continental Drift
Hypothesis
Chapter 14 Lesson 1
p494-500

2. New Vocabulary
• Pangaea (495) – The supercontinent that
all continents today were once a part of
• Continental Drift (495) – A hypothesis
that suggests that continents are in
constant motion on the surface of Earth

4. Pangaea
• Each year, North America moves a few centimeters
farther away from Europe and closer to Asia.
• Nearly 100 years ago Alfred Wegener began an
important investigation to know whether Earth’s
continents were fixed in their positions.
– He proposed that all continents were once part of a
supercontinent called Pangaea.
– Over time Pangaea began breaking apart, and the continents
slowly moved to their present positions.
• Wegener proposed the hypothesis of continental drift,
which suggested that continents are in constant motion
on the surface of Earth.

5. Evidence That Continents Move
• The most obvious evidence for continental
drift is that the continents appear to fit
together like pieces of a puzzle.
• However, scientists were skeptical, and
Wegener needed additional evidence
– 1. Apparent fit of the continents
– 2. Fossil Correlation
– 3. Rock and Mountain Correlation
– 4. Past Climate Data

6. Climate Clues
• When Wegener pieced Pangaea together, he proposed
that South America, Africa, India, and Australia were
located closer to Antarctica 280 million years ago.
• He suggested the climate of the Southern Hemisphere
was much cooler at the time.
– Glaciers covered most of these continents
• Wegener studied the sediments deposited by glaciers in
South America, Africa, India, and Australia.
• He discovered glacial grooves, or deep scratches in
rocks made as the glaciers moved across the land on
neighboring continents today.

8. Fossil Clues

10. Fossil Clues
• Animals and plants that lived on different
continents can be unique to the continent alone.
– Kangaroos are exclusive to Australia. Lions live in
Africa but not S. America.
– Because oceans separate continents, these animals
cannot travel from one continent to another by natural
means
• However, fossils of similar organisms have been
found on several continents separated by
oceans.

11. Fossil Clues
• Fossils of a plant called Glossopteris have been
discovered in rocks from South America, Africa,
India, Australia, and Antarctica.
• Evidence suggests these plants grew in a
swampy environment. Therefore, the climate of
this region, including Antarctica, was different
than it is today
– Antarctica had a warm and wet climate and changed
drastically from 55 milllion years earlier when glaciers
existed.

12. Rock Clues
• Wegener also observed that mountain
ranges and rock formations on different
continents had common origins.
– Today geologists have determined that large-
scale volcanic eruptions occurred on the
western coast of Africa and the eastern coast
of South America at about the same time
hundreds of millions of years ago
• These volcanic rocks are identical in both
chemistry and age

13. Rock Clues
• The Caledonian mountain range in
northern Europe and the Appalachian
Mountains in eastern N. America are
similar in age, structure, and composition.
• If you place the continents together, these
mountains would meet and form on long,
continuous mountain belt.

15. What is missing?
• Wegener continued to support the continent drift hypothesis
until his death in 1930
• His ideas were not widely accepted until nearly 4 decades
later, because he could not explain how they moved
• One reason scientists questioned continental drift was
because it is a slow process
• It was not possible for Wegener to measure how fast the
continents moved
– How could continents push their way through the solid rock of
the sea floor?
– However at that time, the world was only beginning to
understand what the seafloor looked like.
– It took many years after Wegener died before the evidence of
plate tectonics hidden in the rifts on the seafloor to be
discovered.