]> The term geosphere is often used less generally by geologists with reference to the densest parts of Earth, which consist mostly of rock and regolith. [1]. However, the term applies to the four nested geospheres identified since Meteorology (Aristotle) 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, mantle, and core. The outer core is unusual in that it is considered to be a liquid, yet it is a part of Earth's interior.