1. Sea Floor Spreading
The Mid-ocean Ridge

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

3. 60 years ago, in the 1950’s, Sonar was invented.

4. Bats use it!

5. So do dolphins!

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

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

8. They quickly found that the ridge ran around the world!

10. Harry Hess : American Geologist

11. No! Harry Hess, not Harry Potter!

12. Sea-Floor Spreading
Harry Hess
1960

13. An American geologist who studied mid-ocean ridges.
He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.

16. VERY ACTIVE

18. Pillow Rock forms when magma cools in water
Pillow Rock forms when magma cools in water. This is evidence of volcanic activity!

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

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

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

23. Sea Floor Spreading Evidence
pillow lava
magnetic stripes
Drilling rock samples

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

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