1. Sea Floor Spreading
Chapter 9.4

2. Wegener could not explain how the continents moved but . . .
Harry Hess could!
He called his idea
Sea Floor Spreading

3. After World War II: Scientists began to experiment with new tools.
One that measures Sound Waves

4. Echo - Sounding Sound waves were sent to the bottom of
the ocean floor.
The longer it took
the deeper the water.

5. Because of this Scientists Discovered:
Underwater Mountains, Volcanoes & Valleys

6. Mid-Atlantic Ridge The World’s Largest Mountain Range
And it is UNDERWATER!

7. Mid-Atlantic Ridge in Iceland??? (Pingvellir, Iceland)

8. Iceland is on different plates that are moving away from each other (diverging)

9. This is happening all over the Ridge . . .

10. How it works Magma is forced upward & the sea floor spreads apart.
Magma cools & sinks as it flows away forming a high ridge.
The magma then turns to solid crust forming new ocean floor.

11. Proof of Sea Floor Spreading
Rock samples were taken:
Youngest rock near the ridge
Oldest rock was found towards the shore.

12. More Proof – Magnetic Clues
-Magnetite is magnetic.
-Magnetic minerals are attracted to Earth’s magnetic field.

13. When magma containing these minerals cools, it freezes the magnetic mineral grains
so they point in the direction of the Earth’s magnetic field.

14. Over time, Earth’s magnetic field changes (reverses direction).
-As a result, the direction the minerals point changes with it.

15. Paleomagnetism
These changes result in magnetic striping along the ocean floor.
Each beige and red stripe indicates a change in Earth’s Magnetic field.