1. Continental Drift Notes

2. Table of Contents P. 1 Pangaea P. 2 Continental Drift Notes
P. 3 What Would Wegener Say?
P. 4 Sea Floor Spreading Notes
P. 5 Sea Floor Spreading Model
P. 6 Sea Floor Spreading Notes (Con’t)

3. Continental Drift
Alfred Wegener was a German scientist from 1910 that was very curious about the relationship of the continents.

4. Wegener’s Hypothesis was:
That all the continents were once joined together in a single landmass and have since drifted apart.

5. According to Wegener, the continents were once all together forming the supercontinent called Pangaea.

6. Unfortunately, other scientists didn’t believe Wegener because Wegener could not identify the cause of the drifting continents.

7. Mapping the Ocean Floor
During WWI & WWII, scientists discovered that the ocean floor was not flat.
A mid-ocean ridge is an underwater mountain chain where new ocean floor is produced.

8. Scientists have discovered these mid-ocean ridges by using sonar, which is a device that bounces sound waves off underwater objects & then records the echoes of these sound waves.

9. Sea Floor Spreading Notes

10. The sea floor spreads apart along both sides of a mid-ocean ridge – an underwater mountain chain where new ocean floor is produced.
Scientists used sonar to discover the mid- ocean ridges.

11. Sea Floor Spreading
Harry Hess was an American geologist who studied mid-ocean ridges.
Hess proposed the idea that the sea floor spread apart along both sides of the mid-ocean ridge as new crust is added.

12. Evidence for Sea Floor Spreading
Molten Materials:
Scientists found strange rocks shaped like pillows - Such rocks only form when molten material hardens quickly after erupting under water.

13. Magnetic Stripes:
Rocks in the ocean floor have a pattern of “magnetized stripes” – these stripes hold a record of reversals in Earth’s magnetic field because the rock contains iron.

14. Rock Age:
The farther away from the ridge the samples are taken, the older the rocks were and the youngest rocks are always at the center of the ridges.
Younger rock
Older
rock

15. A New Understanding…
Hess's theory of "seafloor spreading" offered a compelling driving mechanism for Wegener's continental drift, but it needed more proof, soon to be known as the Plate Tectonics Theory.