After the grand vistas of cosmic and planetary evolution and the outline of the global processes (what we affectionately call arm waving geology) this up-coming section describes the actual materials the earth is made of, and how these materials are constantly modified, altered sometimes at the surface and sometimes at depth, and how they become the source of new materials. 

Before plate tectonics, geologists tended to consider only crustal materials, under the assumption that the surface of the earth was, with rare exceptions, sealed off from the deeper layers. With plate tectonics, we have come to realize that the crustal materials are really but one part of this giant puzzle that is the earth. We now know that this lithosphere which is so important to us, is but a small portion of an ever cycling earth and that any understanding about materials, their origins and interactions must be rooted in plate tectonic processes and in events that stretch back nearly five billion years in time.