Building a Theory of Plate Tectonics

• The Theory of Plate TectonicsTheory of Plate Tectonics says that the Lithosphere is cracked and broken into pieces called plates that move on top of the convecting Asthenosphere.

• This motion creates mountains, volcanoes, trenches and earthquakes on the surface of the planet.

The Lithosphere is Broken into @ 20 Tectonic Plates

Lithospheric Tectonic Plates

• “Tecton” means “to build”• Move and interact in three

ways to form 3 boundary types:– Convergent- Come together

– Divergent- Separate

– Transform- Slide past each other

The Theory of Continental Drift

The Theory of

Continental Drift (1912)

• Continents were together in one large landmass called Pangea and began drifting apart 250-300 million years ago (mya).

Alfred Wegener (1880-1930)

Geologic Time Line

Pangea – “All Land(Early Permian (290 mya to Early Jurassic (200 mya))” 225 Million Years Ago (mya)

• During the Triassic Period (248-209mya) the continents were still together in a large landmass known as Pangea and began to drift apart about 200 (mya).

• The climate was warm and drywarm and dry for the entire supercontinent.

Tree Fern

Ginko- “living fossil”

Horsetail

Conifer Forest

Ferns

Evidence

Supporting the

Continental Drift Theory

1. Jig Saw Puzzle Fit

• The apparent fit of continental coast lines was the first clue Wegener used to support his theory.

Observe a World Map. Which continents look like they could fit together?

2. Fossil Clues

Glossopteris Fossil (Tree Fern)

• Fern fossil found on 5 different continents:

Africa, South America, Antarctica, Australia and India.

What is the Significance of What is the Significance of this discovery?this discovery?

The presence of this fern in so many areas with widely different climates led Wegener to conclude that all of these areas were one together and shared a similar climate.

Mesosaurus Fossil• Small swimming reptile that

lived in freshwater and about freshwater and about 280 mya. 280 mya. Fossil remains are found in South America South America and Africa.and Africa.

How could these fossils be found so far apart?

They couldn’t swim in salt water and could not swim the distance between the continents, so Wegener hypothesized that they lived on both continents when they were together.

Lystrosaurus Fossil

• Fresh Water Reptile fossil found in Africa

• and India• Could not swim in

salt water and could not swim the distance between oceans

3. Climate Clues

Warm Weathered Plants

• Fossils of warm weathered plants found on island of Spitzbergen in the Arctic.

What does this fossil find suggest about the past climate of Spitzbergen?

Wegener believed that the island drifted from warm weathered areas.

Glacial Deposits and Glacial Grooving

• Glacial deposits and grooved bedrock are found in Southern areas of South America, Africa, India, and Australia.

How could you explain why glacial deposits and grooving were found in areas where no glaciers existed today?

Wegener thought that these continents were once together near Earth’s south pole and covered with glaciers

4. Rock Clues

Mountain Ranges Match

• Parts of Appalachian Mountains are found in Greenland and Western Europe.

If the continents were not connected, then how could mountain ranges match?

Similar Rock Structures

• Similar rock structures were found on South America and Africa.

How do these clues support the idea that the continents were once together?

Weakness of Theory

• Wegener could not explain How or Why the continents drifted apart, so his theory was rejected at the time.

The Initial Break Up• About 180 -200 million

years ago the Supercontinent Pangea began to break up.

• Laurasia was the Northern most continent and consisted of present day North America, Asia and Europe

• Gondwanaland was the Southernmost continent and consisted of South America, Africa, Antarctica, Australia and India

• Panthalassa (“all Ocean”)was the name of the ocean surrounding Pangea.

Watch the Break up of Pangea.

Pangea Animation

http://educatoral.com/img/pangea_anim.gif

"Pangea Ultima"