2. Sea Floor Spreading The Mid-ocean Ridge

3. Vocabulary Sonar Sea-floor spreading Deep-ocean trench Subduction Mid-ocean ridge

4. 60 years ago, in the 1950’s, Sonar was invented. http://www.soundsnap.com/tags/sonar

5. Bats use it!

6. So do dolphins So do dolphins!

7. So does this guy!

8. Sonar brought Wegner’s theory back to life!

9. Sonar is a device that bounces sound waves off underwater objects and records the echos of these sound waves. The time it takes for the echo to arrive indicates the distance to the object. It made it possible for us to observe the ocean floor. http://www.soundsnap.com/tags/sonar

10. Soon, scientists observed a large mountain chain running down the center of the Atlantic ocean.

11. They quickly found that the Mid Atlantic ridge ran around the world They quickly found that the Mid Atlantic ridge ran around the world!

12. Harry Hess : American Geologist

13. Harry Hess No! Harry Hess, not Harry Potter!

14. Sea-Floor Spreading Harry Hess

15. Process that continually adds new material to the ocean floor while pushing older rocks away from the ridge.

16. Moves like a conveyor belt carrying continents with it.

18. New rock forms along the cracks in the ocean crust as molten material erupts from the mantle, spreading out and pushing older rock to the sides of the crack. New rock is continually being added by Sea floor Spreading..

19. If new crust is being added to Earth’s surface, is Earth getting bigger?

20. Subduction is a process where the ocean floor sinks back into the mantle at a deep ocean trench.

27. Three key pieces of evidence!! Sea Floor Spreading is the process…..What is the evidence?

28. Pillow Lava forms when magma cools in water. This is evidence of volcanic activity! #1

29. #2 Magnetic Striping https://www.geolsoc.org.uk/Plate-Tectonics/Chap3-Plate- Margins/Divergent/Mid-Atlantic-Ridge

30. #3 Drilling for Rock Samples: This shows you the age of the sea floor. The red areas are new rocks and the blue areas are the oldest oceanic rock.

31. Iceland is spreading open on the Mid- Atlantic Ridge!

32. Can you see where the Mid-Atlantic Ridge bisects Iceland? This is a rift valley!

33. Sea Floor Spreading Sonar Mid-Ocean Ridge ocean is spreading open!!! pillow lava magnetic stripes Drilling rock samples