17.1 Plate Tectonics

1. 17.1 Plate Tectonics

3. Objectives • Describe one piece of early evidence that led people to suggest that Earth’s continents may have once been joined. • Discuss evidence of continental drift. • Explain why continental drift was not accepted when it was first proposed. Vocabulary • continental drift • Pangaea

4. Drifting Continents • Earth’s surface appears to remain relatively unchanged. • On the geologic time scale, Earth’s surface is changing at rates almost too great to imagine.

7. Three scientists made observations about the earths continents • Abraham Ortelius • Eduard Suess • Alfred Wegener.

8. 1500s noticed the fit of continents on either side of the Atlantic Ocean. Abraham Ortelius - Dutch mapmaker

9. Eduard Suess - Austrian geologist • 1800s • hypothesized that present southern continents had once been joined as a single landmass that he named Gondwanaland.

10. Alfred Wegener German scientist • 1912 proposed the continents moved.

11. Wegner’s Hypothesis – continental drift • continental drift, proposed all Earth’s continents had once been joined.(Pangaea) • Pangaea, (Gr) Pan = all Gaea= Earth • (all the continents had once been joined) • Broke apart 200 million years ago.

12. Continental Drift

13. Evidence from Rock Formations • Areas of similar rock types on opposite sides of the Atlantic Ocean.

14. Evidence from Fossils and Rock Formations

15. Evidence from Fossils • Similar fossils found on widely separated continents. • fossils older than 200 million years when Pangaea broke apart. • Fossils of Glossopteris, a seed fern that resembled low shrubs, have been found on many continents, indicating that the areas had a single climate that was close to the equator.

17. Fossil Record

18. Coal deposits in Antarctica suggested that it must have been closer to the equator. Ancient Climatic Evidence Glacial deposits found in Africa, India, Australia, and South America suggested that these areas had once been covered by thick ice caps. Wegener proposed that the continents were located near the south pole before Pangaea began to fracture.

19. A Rejected Hypothesis • 1900s, most scientists rejected Wegener’s hypothesis of continental drift. • Two unanswered questions: • What forces could move continents • How continents could move without shattering

20. Section Assessment 1. How did Pangaea differ from the present layout of the continents? During Pangaea, the continents were joined and essentially located in one hemisphere from the north to the south poles. Presently, the continents have separated and are distributed in both the eastern and western hemisphere, with the majority of landmass in the northern hemisphere.

21. Section Assessment 2. According to Wegener, what force caused the continents to move? Wegener suggested that the rotation of Earth could be responsible for continental movement.

22. Section Assessment 3. Identify whether the following statements are true or false. ______ Similar rock types are located in South America and Africa. ______ Gondwanaland and Pangaea essentially refer to the same thing. ______ Coal located in India and Africa suggest that they were once located in warmer climates. ______ Geologic evidence suggests that North America, Greenland, and Europe were once connected. true true false true