1. Unit 3: The Dynamic Earth
Mr. Ross Brown
Brooklyn School for Law and Technology

2. How have the continents drifted?
26 October 2015
Do now: How is continental drift like a jigsaw puzzle?

3. Unit highlights
Continental drift and how there was once a single landmass
Seafloor spread as evidence of drift
Plate tectonics
Geologic activity at plate boundaries
Lithospheric plates and convection

4. Coastlines lead to a hypothesis

5. What is Continental Drift?
Mapmakers and explorers noticed similar shorelines on either side of the Atlantic Ocean
Could the continents have once fit together?
1912- Alfred Wegener proposed the theory of Continental Drift; the continents had moved!
This suggested a single landmass: Pangea
Surrounded by super ocean Panthalassa

6. What is Pangea? From late Paleozoic to early Mesozoic eras
Assembled from earlier continental units around 300MYA and began to break apart around 175MYA

7. Fossil evidence for Pangea and drift
Similar fossils found on different continents
Mesosaurus, alive 270MYA, found on Africa’s west coast and S. America’s east

8. Who was Mesosaurus?

9. What other evidence supports the theory of Pangea?
Geological evidence
Mountain ranges spanning continents
Climatic evidence
Glacial debris found across S Hemisphere landmasses that are today warmer

10. Was the theory of Pangea fully accepted?
What was the force that made the continents drift apart?

11. What if continents hadn’t drifted?

12. What if continents hadn’t drifted?

13. Homework #6
26 October 2015
What observations first led to Wegener’s hypothesis of continental drift?
What types of evidence supported Wegener’s hypothesis?

14. What force makes the continents drift?
27 October 2015
Do now: Based on what we discussed yesterday, what is the force that moved the continents apart from Pangea, and still moves them today?

15. What is the Mid-Atlantic Ridge?
Undersea mountain range, with a steep valley running down its center.
Part of an 80,000km system of mid-ocean ridges
In 1940s scientists found that none of the rock there was older than from 175MYA
Continental rock is from up to 4BYA!

16. What are Mid-Ocean Ridges

17. What is seafloor spreading?

18. How did the theory of seafloor spreading develop?
What if the valley at the center of the ridge was a rift, or break?
Magma wells up through this break
Possible if ocean floor moved away from ridge
If seafloor moved, then perhaps continents moved, too?!

19. Homework #6, continued 27 October 2015
Describe the process of seafloor spreading.

20. How did our understanding of plate movements develop?
30 October 2015
Do now: How is ‘plate tectonics’ different from ‘continental drift?’

21. Plate tectonics
The theory that Earth's outer shell is divided into several plates that glide over a plastic inner layer above the core. The plates act like a hard and rigid shell compared to Earth's interior.

22. How did seafloor spread refine the theory of plate tectonics?
Moved beyond notion of “continental drift”
Plate tectonics: the study of the formation of the earth’s crust
Lithosphere: the rocky stuff. Crust and rigid mantle
Asthenosphere: plastic rock on which lithosphere floats

23. Earth’s plates

24. What happens where plates meet?
Divergent Boundaries: plates move away from each other, forming rifts or mid-ocean ridges
Convergent Boundaries: plates collide
Subduction: Oceanic pushed under continental
Obduction: Continental pushed under oceanic
Orogenic: both push upwards
Transform Boundaries: Plates grind past each other

25. Where plates meet

26. What happens where plates meet?

27. How did the continents form?
2 November 2015
Do now: Why are there seashells on the tops of mountains?

28. How does subduction increase continental crust?
As oceanic crust is subducted, some lithosphere is “scraped off” and accumulates on the continent. This is a terrane.

29. What is a terrane?
Pieces of lithosphere with unique geological history

30. How is each terrane unique?
A terrane contains rocks and fossils that are unique from its neighbors
There are major faults at the boundaries of the terrane
The magnetic properties of the terrane do not match its neighbors