KGMK+1.4

toc =sea-floor spreading=

vocabulary

 * mid-ocean ridge** :the longest chain of mountains in the world
 * sonar** :the wave that scientists send down to see how long the mid-ocean ridge is
 * sea-floor spreading** :the process the continually adds new material to the ocean floor
 * deep-ocean trench** :an under water canyon
 * subduction** :is the process which the ocean floor sinks beneath a deep-ocean trench and back into the mantle

mapping the mid-ocean ridge

 * use sonar
 * longest chain of mountains in the world

evidence from sea-floor spreading

 * evidence from molten material,magnetic strips and drilling samples

subduction at deep-open trenches
think of sea-floor spreading as a giant conveyor belt
 * the new oceanic crust is very hot

subduction and Earth's ocean

 * the ocean floor is renewed about every 200 million years
 * the pacific ocean is shrinking
 * the Atlantic ocean is growing