Alternating parallel bands of normal and reversed magnetic polarity are found in the basaltic bedrock on either side of the mid Atlantic ridge. The mid Atlantic is a divergent margin where two plate pulls apart from each other.
At the Atlantic ridge, basalt materials from deeper levels of the crust/asthenosphere rises to the surface.
On either side of the margin the magma cools and solidifies to form new crust.
Basaltic magma contains some metallic minerals that can easily be magnetized to the nature of their domains.
These minerals will align in form of band according to the prevailing condition of the magnetic field at the time of their formation.
This eventually shows magnetic polarity on either side of each plates.
