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.

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 made it possible for us to observe the ocean floor.

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

11. They quickly found that the ridge ran around the world They quickly found that the 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

18. Sea Vents

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

23. This shows you the age of the sea floor. The red areas are new rocks and the blue areas are the oldest oceanic rock.

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

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

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

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

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