DAJB+1.4

toc

Vocabulary

 * Mid-ocean ridge**: The longest chain of mountains in the world.
 * Sonar**: A device that bounces sound waves off under water objects and then records the the echoes of these sound waves.
 * Sea-floor spreading**: The process that continually adds new material to the ocean floor.
 * Deep-ocean trenches**: A deep valley along the ocean floor through which oceanic crust slowly sinks towards the mantle.
 * Subduction**: The process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Mapping the Mid-Ocean Ridge

 * Use sonar to map Mid-Ocean Ridge.

Evidence of Sea-Floor Spreading

 * At the mid-ocean ridge molten material rises form mantle, molten material spreads out and pushes older rock to the sides.
 * Crew found rocks shaped like pillowes.
 * Scientists dicovered rock that make the ocean-floor lie in patterns of magnitized, stripes.
 * Scientists found out that the farther away from the ridge the older the rock is.

Subduction at Deep-Ocean Trenches

 * In deep-ocean trenches subduction allowes the ocean-floor to sink back into the mantel, over tens of millions of years.

Subduction and Earth's Oceans

 * The process of subdution and sea-floor spreading can change the size and shape of the ocean.
 * The Pacific ocean is shrinking, because it has many trenches.
 * The Atlantic ocean is getting bigger because they has few trenches.