1. SEA-FLOOR SPREADING

2. Sea-Floor Spreading

3. Mapping the Mid-Ocean Ridge The mid-ocean ridge is the longest chain of mountains in the world. The mid-ocean ridge is the longest chain of mountains in the world. Scientists mapped the mid-ocean ridge using sonar. Scientists mapped the mid-ocean ridge using sonar. Sonar is a device that bounces sound waves off underwater objects and records it. Sonar is a device that bounces sound waves off underwater objects and records it.

4. Sea-Floor Spreading At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material spreads out, pushing older rock to both sides of the ridge. At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material spreads out, pushing older rock to both sides of the ridge. This process that continually adds to the ocean floor is sea floor spreading. This process that continually adds to the ocean floor is sea floor spreading. CHECK THIS OUT!!

5. Evidence for Sea Floor Spreading In the 1960s scientists found evidence that new material is erupting along the mid-ocean ridge. In the 1960s scientists found evidence that new material is erupting along the mid-ocean ridge. The presence of pillow shaped rocks has showed that molten material has erupted again and again. The presence of pillow shaped rocks has showed that molten material has erupted again and again.

6. Evidence for Sea-Floor Spreading Evidence in the rocks shows that Earth’s magnetic poles have reversed. Evidence in the rocks shows that Earth’s magnetic poles have reversed. The iron bits lined up in the opposite direction and shows this evidence. The iron bits lined up in the opposite direction and shows this evidence.

7. Evidence of Sea-Floor Spreading Evidence from drilling into the sea floor shows evidence of the ages of rocks Evidence from drilling into the sea floor shows evidence of the ages of rocks The closer you get to the mid-ocean ridge the younger the rock. The farther you get, the older the rock. The closer you get to the mid-ocean ridge the younger the rock. The farther you get, the older the rock.

8. Subduction in Deep-Ocean Trenches As the ocean spreads apart, it also plunges into deep water canyons called deep- ocean trenches. As the ocean spreads apart, it also plunges into deep water canyons called deep- ocean trenches. Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle. Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

9. Subduction The processes of subduction and sea-floor spreading can change the size and shape of the oceans. The processes of subduction and sea-floor spreading can change the size and shape of the oceans. Because of this processes, the ocean floor is renewed about every 200 million years. Because of this processes, the ocean floor is renewed about every 200 million years.

10. Subduction in the Oceans The Pacific Ocean is shrinking! This is due to the fact that a deep-ocean trench is swallowing more crust than the mid-ocean ridge can produce. The Pacific Ocean is shrinking! This is due to the fact that a deep-ocean trench is swallowing more crust than the mid-ocean ridge can produce. The Atlantic Ocean however, is expanding! The Atlantic Ocean however, is expanding!