Oceanic Crust - Magnetic Lines

Magnetic Lines

The oceanic crust displays an interesting pattern of parallel magnetic lines, parallel to the ocean ridges, frozen in the basalt. In the 1950s, scientists mapped the magnetic field generated by rocks on the ocean floor. They noticed a symmetrical pattern of positive and negative magnetic lines as they moved along the ocean floor, and the line of symmetry was at the mid ocean ridge. The fact that the anomalies were symmetrical at the mid-ocean ridge was explained by the hypothesis that new rock was being formed by magma at the mid-ocean ridges, and the ocean floor was spreading out from this point. When the magma cooled to form rock, it aligned itself with the current position of the north magnetic pole of the Earth (which has reversed many times in its past) at the time of its cooling. New magma forced the older cooled magma away from the ridge. Approximately half of the new rock was formed on one side of the ridge and half on the other.