Theory of Continental Drift

Review• The earth is composed of layers.• Crust

• Outermost layer• Thinnest• Composed of continental crust and ocean crust• Broken into sections, or plates

• Mantle• Uppermost section is solid and includes the crust

(Lithosphere)• Middle section is pliable, similar to silly putty

(Asthenosphere)• Lower section is solid

• Outer core• Made of liquid iron and nickel

• Inner core• Made of solid iron and nickel

A Puzzle

• How do you put a puzzle together? • What do you look for?• Do you notice anything on this map?• Think “puzzle pieces”

Alfred Wegener

•German scientist who noticed the same thing you did – that South America and Africa look like pieces to a puzzle.

•This observation led to his hypothesis that all the continents were once joined together, and have since drifted apart.• Let’s see what he thought!

Theory Rejected!

• The scientists of Alfred Wegener’s day did not accept his theory.

• Why?• He had no explanation of how the continents moved!• So he collected evidence to prove them wrong.

Landform Evidence

• When Wegener placed South America and Africa next to each other, he noticed that a mountain range in Argentina matched up with a mountain range on other continents.

• He also noticed that coal fields in Brazil were identical to coal fields in South Africa.

• What did he infer from this evidence?

Fossil Evidence

• Wegener also used fossil evidence to support his theory. • Glossopteris

• Fernlike plant• Grew in tropical climates (warm, wet areas)• Fossils found in Antarctica, as well as Africa,

South America, Australia and India.• The seeds were too large to be carried by wind• The seeds were too fragile to survive a trip in

the ocean• How did they develop on all those continents?

• What did he infer from this evidence?

Fossil Evidence

• Ancient reptiles• Mesosaurus• Lystrosaurus• Cynognathus

• These reptiles were land animals, and lived near fresh water.

• Wegener found fossils of these reptiles on many continents, too far apart for them to have traveled that distance, UNLESS?

Climate Evidence

• Sptizbergen is an island that is north of Norway in the Artic Ocean.

• Coal forms in swampy, tropical areas.• Coal deposits are found on Spitzbergen.• What did Wegener infer from this evidence?

More Climate Evidence

• Continental glaciers are thick layers/rivers of ice that move across the land

• Because of their size and weight, they leave grooves, or striations, on the surface of the land.

• Wegener found striations left by glaciers in South Africa (glaciation).

• What did Wegener infer from this evidence?• Did you know that there are glacial striations in

Rhode Island?• What can you infer about Rhode Island?

Let’s Put It All Together!• http://www.teachersdomain.org/asset/lsps07_int_bio

geography/• Puzzle like fit of continents• Matching mountain ranges• Same fossils found on many continents• Glaciation and other climate clues

Now your turn:What do you think Pangaea looked like?

Questions?