| A | B |
|---|
| mid-ocean ridge | the longest chain of mountains in the world |
| sonar | a device that bounces sound waves off underwater objects and then records the echoes of these sound waves |
| Iceland | is an example of mid-ocean ridge |
| What happens 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. |
| sea-floor spreading | The process that continually adds new material to the ocean floor |
| 3 examples of sea-floor spreading | molten material, magnetic stripes, drilling samples |
| molten material | looks like toothpaste squeezed from a tube and quickly dried |
| magnetic stripes | rock that hardens with iron, that is like tiny compass needles |
| drilling samples | pieces of the sea floor from 6 kilometers deep that was brought up |
| deep-ocean trenches | the ocean floor plunges into deep underwater canyons |
| subduction | the process of ocean floor sinks beneath a deep-ocean trench and back into the mantle |
| deep-ocean trenches and subduction | 2 processes that allows part of the ocean floor to sink back into the mantle, over tens of millions of years |
| Pacific Ocean | shrinking ocean |
| Atlantic Ocean | expanding ocean |
