KYTL+1.4

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Vocabulary:

 * subduction**-process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle
 * mid-ocean ridge**-longest chain of mountains in the world
 * sonar**-device that bounces sound waves off underwater objects and then records the echoes of these sound waves
 * sea-floor spreading**-process that continually adds new material to the ocean floor
 * deep-ocean trenches**-deep underwater canyons

Summary

 * There are many bizzare animals deep under the water

Mapping the Mid-Ocean Ridge

 * curves like seam of baseball
 * under hundred of meters of water
 * more than 50,000 kilometers long

Evidence from Sea-Floor Spreading

 * At the mid-ocean ridge, molten material rises from the mantle and erupts.
 * The molten material then spreads out pushing older rock to both sides of the ridge
 * Evidence from Molten Material
 * found strange rocks shaped like:
 * pillows
 * toothpaste
 * such rocks can form only when molten material hardens quickly after erupting under water
 * Evidence from Magnetic Stripes
 * when cooled, iron bits inside lined up in direction of Earth's magnetic poles
 * rocks hardened at the same time has the same magnetic memory
 * when rocks hardened completely, it locked the iron bits in place giving the rocks a permanent "magnetic memory"
 * Evidence from Drilling Samples
 * found-the farther from ridge the sample was taken, the older the rocks were-shows sea-floor spreading took place

Subduction at Deep-Ocean Trenches

 * convection currents under the lithosphere pushes new crust that forms at the mid-ocean ridge away from the ridge and toward a deep ocean trench
 * at deep-ocean trenches, subduction allows part of the ocean floor to sink back into the mantle for over tens of million years

Subduction and Earth's Oceans

 * Sea-floor spreading can change the size and shape of the ocean
 * Subduction in the Pacific Ocean
 * the Pacific Ocean is shrinking because sometimes a deep-ocean trench swallows more oceanic crust than the mid-ocean ridge can make
 * Subduction in the Atlantic Ocean
 * the Atlantic Ocean is expanding because it only has a few short trenches so the ocean floor has nowhere to go