Sea-Floor Spreading 4-4 Notes

1. Sea-Floor Spreading 4-4 Notes

2. …still waiting for the answer… How could the continents plow through hard, solid ocean floor?

3. Improved techniques and instruments • Sonar = a device that bounces sound waves off under-water objects to generate an image.

4. Mid-Ocean Ridge • Mapped using sonar in mid-1900s. • Is the longest chain of mountains in the world.

6. Mid-Ocean Ridge • Has a deep crack running through its center = rift valley.

7. Harry Hess • Examined maps of the mid-ocean ridge and realized that Wegener may have been right! • 1960 – suggested that the ocean floors move like conveyor belts.

8. How it works: • Molten material rises from the mantle and erupts at the mid-ocean ridge. The molten material then spreads out, pushing older rock to both sides of the ridge = sea-floor spreading

9. Sea-floor spreading = the process that continually adds new material to the ocean floor.

10. Local Sea-Floor Spreading:

11. Evidence of sea-floor spreading • Molten material • 2) Magnetic stripes • 3) Drilling samples

12. Molten Material • Alvin found pillow-basalt rocks along bottom. • = evidence that molten material is erupting at mid-ocean ridge.

13. Magnetic Stripes • Evidence shows magnetic reversals (poles reverse themselves).

14. Magnetic Stripes • Molten rock cools and hardens with magnetic memory. • Seafloor provides permanent record of magnetic reversals.

15. Magnetic Stripes • Shows that new seafloor is being created.

16. Drilling Samples • Rock samples drilled from the seafloor. • Tests found that youngest rock was always at the mid-ocean ridge. • Rocks get older farther from mid-ocean ridge.

17. Ages of Rock on Ocean Floor

18. The End!