The striped magnetic pattern develops because, as oceanic crust pulls apart, magma rises to the surface at mid-ocean ridges and spills out to create new bands of ocean floor. Ferromagnetic minerals in the hot magma align themselves with the Earth's magnetic field, which completely reverses its north-to-south polarity every now and then, and freeze in that alignment as the magma cools. Later, after the planet's magnetic field flips again, the next stripe of new ocean floor aligns its polarity in the opposite direction.
