Identify how magnetic symmetry can be used as evidence of sea floor spreading?

At the mid ocean ridge the oceanic plates are separating taking half of the lava on either side. The iron particles in the lava become oriented with the earth's magnetic filed and are frozen in place. Over time the magnetic poles move around and the orientation of the iron shows as polarity stripes, or flips in the poles from north to south. The stripes are identical on either side of the mid ocean ridge demonstrating that the sea floor is spreading in both directions.