<P> Since then , it has been shown that the motion of the continents is linked to seafloor spreading by the theory of plate tectonics . In the 1960s , the past record of geomagnetic reversals was noticed by observing the magnetic stripe `` anomalies '' on the ocean floor . This results in broadly evident `` stripes '' from which the past magnetic field polarity can be inferred by looking at the data gathered from simply towing a magnetometer on the sea surface or from an aircraft . The stripes on one side of the mid-ocean ridge were the mirror image of those on the other side . The seafloor must have originated on the Earth 's great fiery welts , like the Mid-Atlantic Ridge and the East Pacific Rise . </P>
what observation led to the theory of seafloor spreading
magnetic stripe `` anomalies '' on the ocean floor