Four data sets are required to put constraints on the tectonic evolution of the southern rim of the Pacific Ocean basin I . data bearing on the dispersal of the major Gondwanaland continental fragments and the birth of the Southern Ocean, 2. data bearing on the interaction of the Pacific Ocean basin lithosphere with the South American, Antarctic, and Australasian continental masses, 3. data bearing on.the evolution of the Scotia Sea floor, and 4. data bearing on the evolution of the various continents, microcontinents. and volcanic arcs.