1. Continental Drift & Plate Tectonics
Chapter 9, Sections 1 & 2

2. An Idea Before its Time
In 1915, an eccentric German geologist, Alfred Wegener, proposed the hypothesis of continental drift
Continental Drift – hypothesis that proposed that the continents had all been joined together to form one “supercontinent”, the supercontinent broke into pieces and drifted apart forming the modern continents
Pangaea – the supercontinent from continental drift, means “all land”

3. Breakup of Pangaea

4. Evidence: The Continental Puzzle
Wegener first thought the continents had been joined from the almost perfect fit of the shorelines of Africa and South America

5. Evidence: Matching Fossils
Fossil evidence for continental drift includes several fossil organisms found on different landmasses.
The Mesosaurus, an aquatic reptile, has fossils that are limited to eastern South America and southern Africa, if it were able to swim well enough to make it across the Atlantic Ocean, the fossils would be more widespread
The idea that there were widespread land bridges was the most widely accepted theory to there being similar fossils in distant places

6. Matching Fossils

7. Concept Check
How does the distribution of Mesosaurus fossils provide evidence for continental drift?
Mesosaurus occurs only in eastern South America and southern Africa

8. Evidence: Rock Types and Structures
If the continents existed together in Pangaea, they should have matching rock types and features should match closely in age and type
Rock evidence for continental drift exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean
The Appalachian Mountains on the Eastern side of North America have similar ages to mountains in the British Isles and Scandinavia

9. Matching Mountain Ranges

10. Concept Check
How does the location of mountain chains provide evidence of continental drift?
If mountain chains can be continued across present-day oceans, they provide evidence that the areas were once connected

11. Evidence: Ancient Climates
Wegener was a meteorologist by profession and so looked closely at the ancient climates of the different continents
He found evidence for massive glaciers all over Africa and South America that matched each other in age and position
The problem was figuring out how ancient glaciers were on these now tropical regions, unless the continents moved to their current positions

12. Glacier Evidence

13. Rejecting the Hypothesis
The main objection to continental drift was that it lacked a mechanism
Wegener proposed that the continents “plowed” their ways through the ocean, however no evidence on the ocean floor was ever found to support this
In the years that followed Wegener’s hypothesis, we gained greater knowledge of earthquakes

14. Concept Check Why was Wegener’s hypothesis rejected?
He could not provide a mechanism for the movement of the continents

15. Earth’s Major Plates
According to the plate tectonic theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer; the lithosphere
Plate Tectonics – the theory that proposes that Earth’s lithosphere consists of individual plates that interact in various ways producing earthquakes, volcanoes, mountains, and the crust itself
Plate – segment of the lithosphere, which moves and continually changes shape
The plates move relative to each other at a very slow rate ~5 cm/yr (about the same rate your fingernails grow!

16. Earth’s Major Plates

17. Concept Check What is plate tectonics?
A theory that states that Earth’s rigid outer shell is broken into plates made up of the crust and upper mantle, also known as the lithosphere. A plate moves as a unit with respect to the surrounding plates.

18. Types of Plate Boundaries
The three main types of boundaries are convergent, divergent, and transform fault boundaries
Divergent Boundaries – two plates moving apart and producing new lithosphere
Convergent Boundaries – two plates move together and destroy old lithosphere
Transform Boundaries – two plates grind past each other without the production or destruction of lithosphere

19. Types of Plate Boundaries

20. Assignment Read Chapter 9, Sections 1 & 2 (pg. 248-255)
Do Chapter 9 Assessment #1-30 (pg )
For Section 1: #’s 3, 6, 10, 18, 19, & 21
For Section 2: #’s 1, 2, 4, 8, 11, 12, 15, 16, 20, 28, & 29