1. 7.2 Drifting Continents Objectives: What is continental drift?
How do landforms, fossils, and climate changes show evidence of the changing surface of the Earth?
Explain how sea-floor spreading provides a way for continents to move.

2. Tech Terms:
Alfred Wegener –
German scientist whom in the 1900’s hypothesized that the continents had once been a huge landmass which he called Pangaea (“all lands”).

4. Let’s fit the pieces of Wegener’s puzzle together!
Old book p
Complete Chart & Illustrate!

6. continental drift – the slow movement of continents over Earth’s surface. It was a hypothesis, that was tested.
Why did he believe in this theory?
fossil – any trace of an ancient organism that has been preserved in sedimentary rock.

8. Define and illustrate the following 3 terms: Old book p. 118-122.
Pangea
Wegener
Disbelief

9. Wegener used evidence from landforms, fossils, and climate to support his hypothesis.
Wegener’s hypothesis was rejected because he could not provide an explanation for the force that pushes and pulls the continents.
Where is the math? How can you recreate this experiment?

10. PBS Videos: Why Wegner began his hypothesis!

11. New Evidence to support his claims?
Cooling & Shrinking
Sea Floor Spreading
Molten Material and Magnetic Stripes
Convection Currents

12. Sea Floor-Spreading
1. mid-ocean ridge – longest chain of mountains extending into all of Earth’s oceans, that curves like the seam of a baseball along the sea floor.

14. 2. sea floor spreading – the process that adds new material to the ocean floor at the mid-ocean ridge. Molten material erupts and spreads out through the valley that runs along the center of the mid-ocean ridge. It then pushes aside the rock that was already there.

15. Wegner’s Further Evidence:
Landforms, fossils, climate

16. It’s all about … CONVECTION CURRENTS!!!!!!
Continental Drift inside the mantle (2 min)

17. deep ocean trench – this forms from subduction
Subduction- (the oceanic crust bends downward forming a deep underwater canyon on the ocean floor).

18. deep ocean trench examples

19. 4. subduction – Part 2: when the ocean floor sinks beneath a deep ocean trench and gets swallowed by the mantle.

20. Alaska

21. Sea-floor spreading and subduction can change the size and shape of the oceans.
The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller.
The Atlantic Ocean is expanding!

22. Further Evidence of Continental Drift!

23. So what will happen as these plates in the ocean floor continue to spread?
Earth 100 Million Years from now
Convection Currents in the Earth. One more time, a different way!
Plate tectonics on a cocoa earth - YouTube