• Has the continents always looked as they do now on the map, or have they changed shape or location throughout Earth's history?

• Write your ideas on a sheet of paper.

Alfred Wegener: Pangaea• In early 1915, the German

scientist Alfred Wegener developed a theory that the continents once formed a giant supercontinent that he called Pangaea.

• Pangaea means all lands.• Wegener proposed the

theory of “Continental Drift:” that all the continents had once been joined together in a single landmass and have drifted apart over time.

Evidence for Continental Drift

• Wegener based the idea on 4 different types of evidence:

1. The continents fit together like a puzzle2. Fossil evidence3. Rock type and Structural Similarities4. Paleoclimaitc Evidence

Plate Tectonics

• Even with the pervious stated evidence, Wegener’s idea of continental drift was not accepted, because no one could come up with a reasonable mechanism for the movement of the continents, until about the 1960’s when the development of the theory of plate tectonics.

Plate Tectonics• Plate tectonics – is a theory that

explains how Earth’s exterior is broken into large slabs of lithosphere (plates) that are in continual motion with each other. This movement is due to convection currents.

• A convection current is a cycle created as hot matter rises, cools, and sinks. (Is a cycle created as hot matter rises & cold matter sinks.)

• Where else are there convection currents, or where else do we used convection currents?

Plate Tectonics• Plate tectonics – is a theory that explains

how Earth’s exterior is broken into large slabs of lithosphere (plates) that are in continual motion with each other. This movement is due to convection currents.

• A convection current is a cycle created as hot matter rises, cools, and sinks. (Is a cycle created as hot matter rises & cold matter sinks.)

• Where else are there convection currents, or where else do we used convection currents?– Cloud formation, the water cycle, cooking,

chemistry.• A plate is a large piece of lithosphere that is

able to move about the surface of the earth. Plates move about an inch a year on average. As plates move, they interact with each other.

• What are some of the causes of these interactions?

Plate Tectonics• Plate tectonics – is a theory that explains

how Earth’s exterior is broken into large slabs of lithosphere (plates) that are in continual motion with each other. This movement is due to convection currents.

• A convection current is a cycle created as hot matter rises, cools, and sinks. (Is a cycle created as hot matter rises & cold matter sinks.)

• Where else are there convection currents, or where else do we used convection currents?– Cloud formation, the water cycle, cooking,

chemistry.

• A plate is a large piece of lithosphere that is able to move about the surface of the earth. Plates move about an inch a year on average. As plates move, they interact with each other.

• What are some of the causes of these interactions?– Mountain building, earthquakes, rift valleys,

volcanos, trenches.

Like a Puzzle

• The continents’ fitting so well together is the first suggestion of continental drift.

• Take a look at the maps, and can you see where some of the other continents can fit together?

Fossil Evidence• Fossil - The remains of an

animal or plant preserved from an earlier era inside a rock or geological deposit, often as an impression or in a petrified state.

• Identical fossils were found on widely separated continents: such as Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris.

Lystrosaurus

Break into Groups

• Share your information with your groups.

• Draw or label this information on the map.

• Where are Mesosaurus, Cynognathus, Lystrosaurus, and Glossopteris found?

Rock Type and Structural Similarities

• There are similar rock types on continents on opposite sides of the Atlantic Ocean.

• Also, mountain ranges like the Appalachian Mtns. and mountains in Scotland and Scandinavia (Caledonia Mtns.) are similar in age, structure, and rock types.

• Don’t forget to label these mountains on your map.

Rock Type and Structural Similarities• When the continents are reassembled, the mountain

chains form a continuous belt.

Paleoclimatic Evidence• Glacial till of the same age is found

in southern Africa, South America, India, and Australia – areas that would be very difficult to explain the occurrence of glaciation.

• Also large coal deposits were formed from tropical swamps in N. America and Europe.

• Pangaea with S. Africa centered over the South Pole could account for the conditions necessary to generate glacial ice in the southern continents.

• Where would N. America and Europe be if the coal deposits were formed from tropical swamps?

Paleoclimatic Evidence• Glacial till of the same age is found in

southern Africa, South America, India, and Australia – areas that would be very difficult to explain the occurrence of glaciation.

• Also large coal deposits were formed from tropical swamps in N. America and Europe.

• Pangaea with S. Africa centered over the South Pole could account for the conditions necessary to generate glacial ice in the southern continents.

• Where would N. America and Europe be if the coal deposits were formed from tropical swamps?

• The areas with extensive coal deposits from the same time period occur in regions that would have been equatorial.

One last look at how the continents' drifted.

Questions

• What theory did Alfred Wegener propose?• Continental drift.

Questions

• What is the theory of Continental Drift?• that all the continents had once been joined

together in a single landmass and have drifted apart over time.

Questions

• What are 2 types of evidence for continental drift?

1. The continents fit together like a puzzle.2. Fossil evidence.3. Rock type and Structural Similarities4. Paleoclimaitc Evidence.

Questions

• Why wasn’t Wegener’s idea of continental drift accepted?

• because no one could come up with a reasonable mechanism for the movement of the continents, until about the 1960’s when the development of the theory of plate tectonics.

Questions

• What are some of the causes of plate interactions?– Mountain building, earthquakes, rift valleys,

volcanos, trenches.

Questions

• Are mountains still building/growing?

Questions

• Describe a convection current.

Question/Homework

• Predict what you think the continents of the earth will look like in the future?

Question/Homework

• How has continental drift effected how species evolve over time?