Forty years after Alfred Wegener put forward his controversial continental drift theory (pp.34-35), technological advances revealed a great deal of information about the ocean floor (pp.38-39). The discovery of magnetic stripes by two British research scientists F. Vine and D. Matthews in 1963 suggested that the ocean floor was made of younger rock than the continents. This led to the all-embracing theory of plate tectonics which divides the world into plates, made up partly of continent and partly of ocean. For example, the South American plate includes half the south Atlantic Ocean, as well as the continental mass of South America. New plate is being made all the time at spreading ridges (the submarine mountains found by challenger, p.30) in the oceans, and old oceanic plate material is being recycled in subduction zones