Plate tectonics and reversals of the Earth's magnetic field are responsible for the magnetic stripes found on the ocean floor. When magma flows out of a mid-ocean ridge, small, magnetic minerals in the magma align themselves to point in the direction of the Earth's current magnetic North. Over time, the Earth's magnetic field reverses its north-to-south polarity, and the magnetic minerals point in the opposite direction, creating a striped pattern.
The discovery of magnetic stripes on the seafloor in the 1950s validated the plate tectonics theory for the geological community. The theory of plate tectonics states that the lithosphere, which is the Earth's outer layer, is divided up into a dozens of irregularly shaped plates. Plates have areas of activity called boundaries, and these boundaries are one of four types. Divergent boundaries are where the plates are moving away from each other, convergent boundaries are where two plates meet, and one of the plates slides under the other. When two land masses collide, this is a collisional boundary, and it results in a mountain range. Transform boundaries are when two plates slide against each other, building up tension, resulting in an earthquake when released. The San Andreas Fault is an example of a transform boundary.