Theory of the Earth is a combination reference and textbook that every exploration geologist and research scientist should have on his/her bookshelf. It is also suitable for advanced undergraduate, as well as graduate level geophysics courses. The emphasis is on the origin, evolution, structure and composition of the earth's interior. It treats the pertinent aspects of solid state physics, thermodynamics, geochemistry, petrology, and seismology in sufficient detail for all who seek current information on geochemistry, solid state physics, and physics of the earth or planets.