1. Continental Drift https://www.youtube.com/watch?v=ELd3ebldSTs
Wegener’s Hypothesis

2. Warm Up Research the earthquake from April 16, 2016 and write down 3 interesting things.

3. Evidence: coastline similarities
In the late 1500s, Abraham Ortelius, a Dutch mapmaker noticed the apparent fit of continents on either side of the Atlantic Ocean

4. Wegener 1912, Alfred Wegener, German Scientist
Proposed Continental Drift Hypothesis

5. Continental Drift Hypothesis
Earth’s continents had once been a single landmass
Named the landmass “Pangaea” (means “All Land”)
Named the ocean surrounding Pangaea “Panthalassa” (means “All Seas”)

6. Panthalassa

7. Pangaea Breaks Apart
Wegener proposed that Pangaea began to break apart about 200 mya
The continents began to slowly move to their present positions

11. Evidence for Continental Drift
Evidence for Continental Drift can be found in 4 main areas:
Coastline similarities
Similarities of plant & reptile fossils
Ancient climatic evidence
Geologic patterns of rocks & mountain chains

12. Evidence: fossil similarities
Similar fossils were found on widely separated continents
Examples
Glossopteris: plant that grew in temperate zones; fossils found in wide array of climatic zones today
Kannemeyerid & Labyrinthodont: land-dwelling animals; could not have swam across oceans

13. Evidence: fossil similarities
Ages of these fossils predated Wegener’s time frame for break-up of Pangaea

14. Evidence: fossil similarities

15. Evidence: ancient climatic evidence
Discovered similarities by studying sedimentary rocks
Coal deposits have been found in Antarctica and Coal forms from dead swamp plants

16. Evidence: ancient climatic evidence
Glacial deposits found in Africa, India, Australia, and South America. Once these areas had once been covered by thick ice caps

17. Evidence: geologic patterns
Similar groups of rocks have been observed in the Appalachian Mountains of the United States, Greenland, and Europe
These rock groups predate the breakup of Pangaea
Support Wegener’s idea geologic structures (such as mountains) broke apart as the continents separated

18. Evidence: geologic patterns

19. Hypothesis Rejected
Most scientists rejected Wegener’s hypothesis because of 2 unanswered questions:
What forces could move the continents?
How can forces move without shattering?
Wegener died in 1930, still searching for evidence to prove his hypothesis.

20. Where is evidence found?
1947, scientists begin mapping ocean floor
Enabled by advancements in technology (mostly due to WWII)
Scientists used:
Sonar
Magnetometers – used to construct magnetic maps of the seafloor

21. Evidence from Sonar Sonar revealed existence of:
Ocean Ridges
Undersea mountain ranges with steep, narrow valleys running down the center
In the valley of the ridge is a break (or rift) in the earth’s crust where magma is pushed to the surface
Trenches
Long, narrow depressions on sea floor

22. Evidence from Sonar Studied Trenches & Ridges and found:
Age of rocks that make up seafloor vary and age consistently increases with distance from a ridge
Thickness of ocean-floor sediment increases with distance from ridge

24. Evidence from Magnometers
Paleomagnetism (study of Earth’s magnetic record) helped scientists determine the age of the ocean floor
Molten rock containing iron becomes magnetic as it hardens (on an atomic level, becomes aligned with Earth’s magnetic pole)
Earth’s magnetic pole reverses through geologic time
Magnetic patterns of ocean floor were compared to magnetic patterns of land

26. Theory of Seafloor Spreading
States that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches

27. Magma is forced toward the crust along an ocean ridge and fills the gap that is created.
When the magma hardens, a small amount of ocean floor is added to Earth’s surface.

28. Theory of Seafloor Spreading
This theory was the missing link needed by Wegener to complete his model of continental drift.