Plate Tectonics: Lesson 1

Plate Tectonics: Lesson 1

Pangaea

Nearly 100 years ago, a scientist named Alfred Wegener (VAY guh nuhr) began an investigation. He wanted to know if Earth’s continents had always been in the same place, or if they had moved. Wegener proposed that all the continents were once part of a supercontinent called Pangaea (pan JEE uh).

Over time, Pangaea broke apart, and the continents slowly started moving to where they are now.

Multiple Choice

How did the continents drift over time?

• quickly

• slowly

His hypothesis

Wegener proposed the hypothesis of continental drift. The continental drift hypothesis suggested that continents are in constant motion on Earths surface.

Wegener looked at the coastlines of continents that are now separated by oceans. He saw similarities in their shapes. For instance, Africa and South America seemed have coast that fit together like pieces of a puzzle.

Multiple Choice

Wegeners theory states the continents are in ______ motion.

• fast

• constant

• off and on

FOLDABLE TIME

Take a piece of notebook paper and turn it sideways. Fold the two sides until they meet in the middle(do not overlap. Using scissors, cut each side flap in half. On the front write the following, one on each flap: Rock Clues, Climate Clues, Fossil Clues, and Puzzle-like fit.

Under each flap, write ATLEAST TWO pieces of Wegeners evidence for each that proved that the continents were once connected. The following slides will help you

The need for EVIDENCE- Puzzle-like fit

Wegener knew that he needed evidence to support his hypothesis of continental drift. The most obvious evidence was how the continents fit together like pieces of a puzzle. For instance, Africa and South America seemed to fit together like the pieces of a puzzle But other scientists were doubtful of his hypothesis.

Wegener needed MORE evidence.

Multiple Choice

what was his first and most obvious piece of evidence

• he could feel the continents moving

• he saw one of them move

• the continents look like they fit together like a puzzle

• another scientist told him about it

Fossil clues

There are many animals and plants that live only on one continent. For example, lions live in Africa but not in South America. Because oceans separate the continents, animals cannot travel from one continent to another by natural means. However, fossils of similar organisms have been discovered on different continents that are now separated by oceans.

Fossil Clues continued....

Fossils of a plant called Glossopteris (glahs AHP tur us) have been discovered in rocks from South America, Africa, India, Antarctica, and Australia. Today these continents are far apart and separated by oceans. The plant’s seeds could not have traveled across the oceans.

Climate Clues

Other fossil evidence supported continental drift. Coal beds are in Antarctica, a polar climate today. Yet coal formed from fossilized plants that lived long ago in warm, wet climates. This meant that Antarctica must have been warmer and wetter when these plants were alive. Is it possible that Antarctica was at one time closer to the equator? Did Antarctica move to a colder climate near the South Pole?

Another climate clue used by Wegener to support continental drift came from glaciers. When Wegener pieced Pangaea together, he proposed that South America, Africa, India, and Australia were located closer to the South Pole 250 million years ago.

Climate Clues Continued....

Wegener also studied glacial grooves. Glacial grooves are deep scratches in rocks made as ice sheets move across the land. Wegener found glacial grooves on many different continents which gave us a clue that all of these areas were once connected.

Rock Clues

Some of the evidence used by Wegener to support his idea of continental drift came from rock formations on different continents. The rock formations and mountain ranges seemed to have formed in the same way at the same time. Today geologists know that there were large-scale volcanic eruptions on the western coast of Africa and on the eastern coast of South America hundreds of millions of years ago. Geologists have studied rocks from these eruptions. They found that the volcanic rocks from both continents were identical in chemistry and age. 

Rock clues continued

More evidence of rock clues were found when mountain ranges such as the calendonian and appalachian mountains were found on two different continents.

Rocks in these two mountain chains are similar in age and structure. Both are also composed of the same rock types. If you could place North America and Europe next to each other, these mountain chains would meet. They would form one long, continuous mountain belt,