Science-Sea floor spreading/the theory of plate tectonics

mid-ocean ridges

these form long chains of mountains that rise up from the ocean floor

Sea floor spreading

this adds more crust to the ocean floor. At the same time, older strips of rock move outward from either side of the ridge.

What happens atDeep ocean trenches

In a process taking tens of millions of years, part of the ocean floor sinks back into the mantle, occuring here

Deep-ocean trenches

canons made when the ocean floor gets deepest

subduction

The process by which the ocean floor sinks beneath a deep ocean trench and back into the mantle again