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Chapter 1, Section 4

 

Chapter 1, Section 4

What Is Sea-Floor Spreading?

Harry Hess, an American geologist, was one of the scientists who studied mid-ocean ridges. Hess carefully examined maps of the mid-ocean ridge system. Then he began to think about the ocean floor in relation to the problem of continental drift. Finally, he reached a startling conclusion: Maybe Wegener was right! Perhaps the continents do move.

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In 1960, Hess proposed a radical idea. He suggested that a process he called sea-floor spreading continually adds new material to the ocean floor. In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them. Look at Figure 16 to see the process of sea-floor spreading.

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Sea-Floor Spreading

A diagram of the way the ocean floor forms from hot lava erupting from valleys and hardening into rock.

Figure 16Sea-Floor Spreading Molten material erupts through the valley that runs along the center of some mid-ocean ridges. This material hardens to form the rock of the ocean floor. Applying Concepts What happens to the rock along the ridge when new molten material erupts?

Sea-floor spreading begins at a mid-ocean ridge, which forms along a crack in the oceanic crust. Along the ridge, molten material that forms several kilometers beneath the surface rises and erupts. At the same time, older rock moves outward on both sides of the ridge. As the molten material cools, it forms a strip of solid rock in the center of the ridge. When more molten material flows into the crack, it forms a new strip of rock.

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