1. Plate TEctonics
Drifting Continents

2. Drifting Continents
Aside from earthquakes, volcanoes, and landslides, Earth’s surface appears relatively unchanged on a human time scale
On geologic time scale, Earth’s surface is changing at huge rates
South America is moving away from Africa 2-3 cm/yr
Volcanic islands that make up Hawaii moving NW at 8-9 cm/yr

3. Early Observations of Moving Continents
First people to consider moving landmasses were early mapmakers
Explanations for continent moving included volcanoes, earthquakes, and floods
1912 Alfred Wegener proposed a hypothesis about continental movement

4. Continental Drift Wegener’s hypothesis was called continental drift
Continental drift proposed that Earth’s continents had once been joined as a single landmass
He called the supercontinent Pangaea, Greek word meaning “all the earth”
Proposed Pangaea began to break apart about 200 million years ago
Continents still moving slowly today

6. Evidence of Pangaea
Wegener was first person to base his idea on more than just the puzzle-like fit between continents
This was some of his evidence:
(1) evidence from rock formations
(2) Evidence from fossils
(3)Ancient Climate Evidence

7. Evidence from Rock Formations
When Pangaea began to break apart, large geologic structures like mountain ranges would fracture as continents separated
Based on this, should have similar rock types on opposite sides of the Atlantic Ocean
EX: rocks of Appalachian Mts share similar features with rocks in Greenland and Europe-all of these rocks are older than 200 million years old
See other matching rock types in book p. 445

8. Evidence from Fossils
Similar fossils of different plants and animals that once lived on land were found on widely separated continents
Land-dwelling animals like Kannemeyerid could not have swum great distances that now exist between continents

10. Used fossils from Glossopteris, a seed fern, to show that continents must have been connected and have same climate to support this plant life

11. Ancient Climate Evidence
Studying sedimentary rocks, Wegener found evidence of vast climate change on past environments and climates
EX: Coal forms from dead swamp plants. Coal deposits had been found in Antarctica, supporting the idea that Antarctica must have been closer to the equator at one time

12. Glacial Deposit Evidence
EX: Glacial deposits (in Africa, India, Australia, and South America) nearly 300 million years old led Wegener to believe that these landmasses may have been joined and covered with ice

13. Rejected Hypothesis
Even though Wegener had lots of evidence to support his theory of Pangaea, it was rejected due to two major flaws:
(1) What was causing the continents to move?
(2) How could continents move without shattering the ocean floor?