8th Grade Integrated Science Chapter 14 Lesson 1 on the Continental Drift Hypothesis. This is a short introduction to Alfred Weger and the current evidence used to support his theory. There is a short explanation of the fossil and rock evidence found.

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.