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toc =Sea Floor Spreading=

Vocabulary

 * Mid-ocean ridge**: The longest chain of mountains in the world, mostly underwater.
 * Sonar**: Sound waves that bounce off objects so scientists can tell whats at the bottom of the ocean.
 * Sea-floor spreading**: Harry Hess's theory that 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.
 * Deep-ocean trenches**: A deep-ocean trench 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.

Sea-floor Spreading:

 * Molten Material erupts
 * creates new rock
 * puses old rock back into trench into mantle

Evidence from Molten Material:

 * Rocks at bottom of the ocean look like pillows just like when lava cools
 * examined with submersible called //Alvin//

Evidence from Magnetic stripes:

 * Ocean floor has a pattern of stripes that are magnetic
 * Magma has iron so when the magma comes out the iron lands on the rock
 * called magnetic memory

Evidence from Drilling Samples:

 * The rocks on the ocean floor gave these results
 * Rocks farther from the mid-ocean ridge were older
 * The closer the rocks were to the mid-ocean ridge the newer they were

Subduction and the earths oceans:

 * Subduction is when old rock goes into a trench and back in the mantle when sea floor spreading occurs.
 * Pacific ocean is getting smaller because the trench is too big
 * Atlantic ocean is getting bigger because the trench is too small.

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