Sea­Floor Spreading pg. 23­29 September 25, 2013 sea floor cools sea floor ridge sonar to determine distance to an object sea­floor spreading molten material that erupts and cools Sea­Floor Spreading pg. 23­29 September 25, 2013 molten material magnetic strips drilling samples The further away from the ridge the samples were taken, the older the rocks were. The younger rocks were always in the center of the ridges. deep­ocean trench The process by which ocean floor sinks beneath a deep­ocean trench and back into the mantle. Sea­Floor Spreading pg. 23­29 September 25, 2013 convection currents sea­floor spreading size and shape convection currents The ocean is changed in size and shape. True True The Atlantic Ocean has only a few short trenches. The spreading ocean floor has nowhere to go.