JLKP+1.4

1.4 Sea-Floor Spreading
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= = = = Vocabulary:

= = Mid-Ocean Ridge-the longest chain of mountains in the world Sonar-a device that bounces sound waves off underwater objects and then records the echoes of these sound waves Sea-Floor Spreading-the process that continually adds nes material to the ocean floor Deep-Ocean Trenches-deep underwater canyons where the ocean floor plunges; forms where the oceanic crust bends downward Subduction-the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle Outline:


 * Mapping the mid-ocean ridge


 * Sonar is used to map the ocean floor
 * Evidence for Sea-Floor Spreading
 * Harry Hess studied mid-ocean ridge and thought of sea floor as a conveyor belt at mid-ocean ridge, molten material rises from the mantle and erupts; molten material spreads out, pushing older rock to both sides of ridgeand cools down
 * Evidence from Molten Material


 * scientists found strange rocks shaped like toothpaste squeezed from a tube only forms from when molten material hardens quickly after erupting underwater
 * Evidence from Magnetic Stripes


 * Earth's magnetic poles reversed themselves stripes going north and south side by side patterened
 * Evidence from Drilling Samples


 * used Glomar Challenge to dig up samples found that farther frm the ridge=older rock and closer to ridge= newer rock
 * Subduction at Deep-Ocean Trenches


 * at deep ocean trenches, subduction allows floor to sink into mantle
 * Subduction and Earth's Oceans

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 * subduction and sea-floor spreading can change the size and shape of the ocean
 * Subduction in the Pacific Ocean

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 * Pacific Ocean many deep trenches for subduction- floor getting smaller
 * Subduction in the Atlantic Ocean
 * Atlantic Ocean has little shallow trenches for subduction- floor has nowhere to go; floor gets bigger