1. Continental drift: an idea before its time
Alfred Wegener
Proposed idea of Continental Drift
Continental drift hypothesis
Supercontinent (one) called Pangaea began breaking apart about 200 million years ago
Continents broke apart and then "drifted" to present positions

2. Fossil Evidence
Both Mesosarus and Glossopteris were organisms that would not of been able to travel to the different continents at the distances that the continents are at today.

3. Glossopteris

4. Mesosaurus

5. Mesosaurus

7. Wegener’s matching of mountain ranges on different continents

8. Paleoclimatic (Ancient Climate) evidence

9. Glacial Striations

10. Glacial Remnants

11. Pangaea approximately 200 million years ago

12. Pangaea Breakup
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

13. Why was Wegener rejected?
People couldn’t observe the plates moving
The main objection to Wegener's proposal was its inability to provide a correct mechanism because he did not know about the structure of the Earth
In other words, he couldn’t explain HOW and WHY the continents drift.
Wegner did not have a good reason for the driving force of movement of the plates.
He claimed it was the same forces that influence tides (gravity).

14. Harry Hess USS Cape Johnson
During the war, Harry Hess discovered that the ocean floor was not smooth like everyone assumed but had:
Canyons, trenches, crevasses, and volcanic seamounts

15. In the 1950’s, oceanographers discovered that:
The largest and most extensive mountain chain on Earth was mostly underwater

16. The Earth seemed to be splitting apart at the seams
People were surprised at how large the Mid-Atlantic Ridge was: Drilling machines took core samples, which showed that: Rocks were young at the mid- Atlantic ridge but became older as you moved away from it
Glomar Challenger

17. Harry Hess realized that:
New ocean crust was being formed on either side of the ridge and was then pushed away from it as new crust came along behind
This process became known as:
Sea-floor Spreading

18. Ocean Rocks lasted only: as long as it took them to travel to shore
Hess was ignored for this idea

19. Sea-floor spreading animation

20. Other researchers found :
Magnetic stripes in ocean-floor rocks.
Magnetic particles in molten rock line up in the direction of Earth’s magnetic poles.
The Magnetic Poles of the Earth flip-flop
When rock hardens, a permanent record of Earth’s magnetism remains in the rocks.

21. Magnetic Reversal Animation

23. 2 men from Cambridge drew all the strands together:
In 1963 they used magnetic studies to prove Hess’s theory
Suggested that this meant the continents were moving too
Most scientists finally accept the theory in 1964 and agree to call pieces of moving crust “plates”
Some geologists still rejected the idea into the 1980’s

24. Why is magnetic reversal
strong evidence for
sea-floor spreading?
Lets do an activity – each table group will need:
2 colored pencils (2 different colors)
1 manila folder with a slit cut into it
1 piece of paper
Some tape
Scissors

25. Sea Floor Spreading classroom activity
Cut your piece of paper in half lengthwise so you have 2 long, skinny pieces.
Tape the shorter ends of your two pieces of paper together like this:
Paper 1
Paper 2
Tape

26. Fold the two papers at the tape line
Spread the manila folder over the sink so the slit is above the sink and tape it into place on the desk.
Feed the taped end of the paper through the slit of the folder. Push it through until you have about an inch of the free ends sticking out of the folder.
Two group members will grab one of the free ends of the paper sticking out of the folder. The 3rd member will have the colored pencils ready.

27. 7) Upon the teacher’s instructions, you will begin to SLOWLY pulling your hands apart (while holding onto the paper) until you hear “STOP”.
8) The third member will take 1 color and color in the paper that is now pulled out of the center slit.
9) We will repeat steps 7 & 8 several times, switching colors after each stop to represent the flipping of the Magnetic Poles.

28. Analysis
Complete the questions on the back of yesterday’s note sheet.