What is Differentiation? It is my humble opinion that differentiation is one of the primary driving forces of our planet, so pay attention. To understand the process we have to begin by agreeing on several assumptions: 1. Different earth materials have different densities. 2. Given a chance, all materials will sort themselves by density, with the heavier material sinking and the lighter material rising. 3. The interior of the earth is not a "solid" as we understand the term, but rather in a semi-plastic state which allows ions to migrate (more or less) at will. 4. The earth's interior is zoned by density, with the heaviest material at the center (the core), and the lightest stuff floating about at the surface (the crust). Differentiation is this separation process. Differentiation has been taking place since the formation of our planet 4.6 billion years ago, and is still occurring today. It will continue until one of two things happen: 1. The process is complete and ALL earth materials have sorted themselves relative to all other materials, or... 2. The earth's internal heat drops to a point where the earth is so solid that further ion migration is impossible and the remaining material is essentially frozen in place. In this scenario the earth is basically cold and dead. I like the second choice as the one which will finally stop the differentiation process, although this is probably so far in the future that the earth will have plenty of time to float a bunch more light stuff to the surface. Please note that when the earth dies internally, external (surface) death cannot be far behind, at least for life-forms which exist on land. From a regional point of view, there are really only two earth processes: tectonic forces which build high spots, and surface weathering which tears them down. Over the course of geologic time, the two are in balance (at the local level one or the other is always winning). But, when the earth dies on the inside, so do the tectonic forces which keep making landforms which stick up above the ocean. In very short order the land surface will be eroded to wave base, and we will all have to learn the backstroke!