1. Sea-Floor Spreading
And the Mid Ocean Ridge

2. Magma erupts along the mid-ocean ridge. This happens slowly.

3. New crust (sea floor) is formed as magma cools and slowly pulls away from the ridge.

4. Older rock becomes more dense and sinks down into the mantle at deep ocean trenches in a process called subduction.

5. Sea-Floor Spreading
Animation

6. Earth’s polarity changes at irregular intervals
Earth’s polarity changes at irregular intervals. Evidence of this is found in the magnetized “stripes” of the ocean floor rock.

7. Evidence of Sea-Floor Spreading
Molten material- rocks show evidence of molten material erupting again and again along mid-ocean ridges
Magnetic stripes- iron bits in rock on both sides of the mid-ocean ridge lineup to point either north or south. The pattern is the same on each side of the ridge.
Rock samples- younger rock found near ridge and older rock found away from ridge