Sea Floor Spreading Section 4 page 141-147

2. Sea Floor Spreading Section 4 page 141-147 29. In the mid- 1900’s scientists used sonar to map the ocean floor’s topography. They discovered mid ocean ridges which are like mountains on the sea floor. These mountains look like seams on a baseball.

3. Wow, look at this mid- ocean ridge!

4. 30. In sea-floor spreading, the floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyer belts.

5. Evidence from molten material 31. At the mid ocean ridge, scientists found rocks that look like pillows and as though it has been squeezed from a tube of toothpaste.

6. Evidence of Sea Floor Spreading 32. The earth has a magnetic field which magnetizes the iron in the molten rock. The rock solidifies recording the north south direction of the earth’s magnetic field at the time. This record shows that the magnetic field of the earth has reversed many times. North / south South/ north 33. Rock samples taken close to the ridge are younger than ones farther away. (Drilling samples)

7. 35. Is the Atlantic Ocean getting wider or narrower? Answer- Wider!

8. Subduction page 146 34.The sea floor plunges down in what are called deep ocean trenches. This usually happens at the continental crust.