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Chapter 4 Section 4: Sea-Floor Spreading __Key Terms__
 * Mid-ocean Ridge- An under sea mountain chain where new ocean floor is produced
 * Sonar - A device to determine the distance of an object under water by recording echoes of sound waves
 * Sea-floor Spreading - The process by which molten material adds new oceanis crust to the ocean floor
 * Deep-ocean Trenches -A deep valley along the ocean floor beneath which oceanic crust slowly sinks towards the mantle
 * Subduction -A process by which oceanic crust sinks beneath a deep-ocean trench and back into the mantle at a colliding plate boundary

//** Evidence for sea-floor spreading.**// Molten material, magnetic stripes, and drilling samples all are evidence for the sea-floor spreading theory. New materials have been found erupting along the mid-ocean ridges by scientists going down in a mini submarine. Rocks in the deep look like they were squeezed and fluffed because these rocks are molten material, they harden very quickly under water. With these rocks, it showed molten material has erupted repetively along the mid-ocean ridges. Magnetic stripes in the rock of the ocean floor show the direction of Earth's magnetic field as the rock is hardening. Drilling samples help to show that sea-floor spreading really occured because the farther away from a ridge the samples were taken, the older the rocks were. In the center of the ridges, the younger the rocks were. //**What is a subduction at a trench?**// Ocean floor created along the mid-ocean ridge will be destroyed at a deep-ocean trench,the process of subduction goes like this. The sea-floor spreading and subduction both move the ocean floor. New ocean floor occurs, and it is hot, but once it moves away from the mid-ocean ridge it becomes denser.Gravity pulls it beneath the trench, and it sinks. Basically, it gets hot, it moves, then it becomes cold and sinks! By: Hannah Hauser
 * //What is a mid-ocean ridge ?//** Mid-ocean ridges curve along the sea floor, and they extend to all oceans. A lot of mountains in the mid-ocean ridge system are hidden under many meters of water where they lay, but in some places the ridge may poke just above the surface.
 * //What is sea-floor spreading //?** Once a man named Alfred Wegener had a theory of which the continents moved apart at one point. The sea-floor spreading supports his idea because the sea floor spreads apart along both sides of the mid-ocean ridge and then adds on new crust. With this information,the sea-floor was spreading and carrying the continents along with it.