Transcript Drifting continents

Earth’s Drifting Continents
Earth’s Drifting Continents
Key Concepts
1. What was Alfred Wegener’s hypothesis about
the continents?
2. What evidence supported Wegener’s
hypothesis?
3. Why was Wegener’s hypothesis rejected by
most scientists of his day?
Earth’s Drifting Continents
Key Terms
Continental Drift
Pangaea
Fossil
Continental Drift
• A hypothesis proposed by Alfred
Wegener
• States that the Earth once had a single
landmass that broke up into large
pieces, which have since drifted apart.
Wegener named this continent Pangaea.
• Wegener was the first to build a detailed
scientific case to support this idea.
• He studied land features, fossils, and
evidence of climate change
Evidence From Land Features
• When Wegener pieced together
maps of Africa and South America
An ancient folded mountain chain in
S. Africa matches one in Argentina
• Coal fields in Europe match those in
North America
• Coal fields with distinctive layers in
Brazil match ones with identical
layers in Africa
Evidence from Rocks
• Rock formations in Africa line up with
formations in South America
• Rock deposits left by glaciers are similar in the
different continents suggesting they were left
from the same glaciers.
– Deep scratches in rocks show that glaciers once
covered South Africa
– Many glacier deposits found in warm areas. Must
have been close to poles at one time
• Other rock deposits come from coral reefs,
found in colder climates today, must have been
closer to the equator at one time.
Evidence from rock formations
Evidence from fossils
• Fossils are the remains or traces of organisms
that lived long ago.
• Glossopteris fossils, located in rocks 250 million
years old found in S. America, Africa,
Australia, India and Antarctica
• Glossopteris is a fernlike plant with seeds too
large and fragile to have traveled great
distances. Suggests that these places must once
have been closer together.
• Fossils of the freshwater reptiles Mesosaurus
and Lystrosaurus have been found in places
separated by oceans.
• Neither reptile could have swum great
distances in salt water
Fossils
Mesosaurus
Glossopteris
Lystrosaurus
Evidence from Climate
 As a continent moves closer to equator
it becomes warmer
 As a continent moves toward the poles,
it becomes colder
 The continents carry fossils that were
formed in its previous location
Example:
Spitsbergen, an island in the Arctic
Ocean, has fossils of tropical plants
Wegener’s Hypothesis Rejected
• Wegener tried to explain how continental drift
could take place.
• He theorized that the continents plowed across
ocean floor
• He couldn’t explain the force needed to push or
pull the continents
• Scientists rejected his idea because he couldn’t
identify the cause of continental drift
Pangaea
Wegener Hypothesis of
Continental Drift