FIGURE 2 Schematic of the solid Earth cycle, beginning with rifting of ancient lithosphere, through creation of a new ocean basin by seafloor spreading, plate modification during passage over the mantle, subduction and continental addition, and continental collision, followed ultimately by another episode of continental rifting. This process through time leads to evolution and differentiation of the mantle, and mantle processes in turn influence all components of the cycle. Source: FUMAGES (1998), p. 9.

formation and destruction of the crust and mantle lithosphere, and its interactions with the hydrosphere and biosphere. Recent advances in geophysical and geochemical observation techniques, combined with the computational capability to evaluate the effects of nonlinear, open systems, have led to the development of predictive models of the mid-ocean ridge system based on simple, geodynamic parameters. Based on these advances, it seems likely that a general theory of mantle differentiation and lithospheric genesis will emerge in the next ten to twenty years. To produce this theory, we will have to concentrate research on the upper and lower boundaries of the lithosphere—the regions of interaction with the underlying convective mantle and the overlying hydrosphere and biosphere. Some of these boundaries are difficult to observe, and progress will require development of new techniques to image, for example, the base of the lithosphere in considerable detail.

Study of the seafloor provides one of the primary windows into a multitude of Earth processes, and the linkages between the various parts of the whole Earth system make the new observational data and quantitative models pertinent to a broad spectrum of Earth problems. Therefore, many of these developments will be multi-disciplinary, involving scientists from outside the oceanographic and solid Earth communities.