2. Sea Floor Spreading The Mid-ocean Ridge

3. Vocabulary Mid-ocean ridgeMid-ocean ridge SonarSonar Sea-floor spreadingSea-floor spreading Deep-ocean trenchDeep-ocean trench SubductionSubduction

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 Aquaman!

8. How did sonar bring Wegner’s theory back to life?

9. Sonar made it possible for us to observe the ocean floor.

10. Scientists observed a large mountain chain running down the center of the Atlantic ocean.

11. Scientists found that the mountain range connected with others and encircled the globe Scientists found that the mountain range connected with others and encircled the globe!

12. Mapping the Mid-ocean Ridges Ridges connect and curve around the globe like a baseballRidges connect and curve around the globe like a baseball Ridges lie hundreds of meters below the surface of the oceanRidges lie hundreds of meters below the surface of the ocean Most ridges are underwaterMost ridges are underwater Section of ridge that is on land is East African Rift ValleySection of ridge that is on land is East African Rift Valley

13. The discovery and study of the mid- ocean ridges led to the theory of sea floor spreading

14. Sea-Floor Spreading Harry Hess

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

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

17. Seafloor spreading- new ocean crust is formed at ocean ridges and destroyed at deep sea trenchesSeafloor spreading- new ocean crust is formed at ocean ridges and destroyed at deep sea trenches –Magma forced toward crust –Fills gaps and hardens –Forms new ocean floor

19. Divergent boundary-Divergent boundary- –Moving apart –Most are found on seafloor –Form ocean ridges –When on continent, form rift valley

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

21. Magnetic reversal- change in earth’s magnetic fieldMagnetic reversal- change in earth’s magnetic field –Same as present field- normal polarity –Opposite to present- reversed

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

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

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

25. Sea Floor Spreading Sonar Mid-Ocean Ridge Ocean is spreading open!!! Pillow Lava Symmetrical Magnetic Stripes Symmetrical Age Patterns Newest Rock at the Ridge

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

27. Convergent boundary-Convergent boundary- –Moving toward each other –Classified according to type of crust involved –Oceanic crust mostly basalt –Continental crust granite and sedimentary rock –Oceanic-oceanic- subduction occurs (one plate descends) creates deep sea trench, forms arc of volcanic islands: Mariana trench and islands

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

31. Ridge push- forces in mantle cause asthenoshere to riseRidge push- forces in mantle cause asthenoshere to rise –Pushes oceanic plate toward trench –Could create drag on lithosphere Slab pull- sinking region of mantle convection sucks oceanic plate downwardSlab pull- sinking region of mantle convection sucks oceanic plate downward