The term geosphere is often used to refer to the densest parts of Earth, which consist mostly of rock and regolith. The term originally applies to the four nested geospheres identified since Aristotle's "Meteorologica" with the states of terrestrial matter: solid (earth), liquid (water), gas (air), and plasma (fire). The nested geospheres then include the asthenosphere, lithosphere, hydrosphere, atmosphere, and the ionosphere or plasmasphere. The dense geosphere is also subdivided into the crust… (More on Geosphere)