Earth’s Drifting Continents

Earth’s Drifting ContinentsKey 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

Glossopteris

Mesosaurus

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 locationExample: 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