The term originally 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.
In modern texts, geosphere refers to the solid parts of the Earth and is used along with atmosphere, hydrosphere, and biosphere to describe the systems of the Earth. In that context, sometimes the term "lithosphere" is used instead of geosphere, however the lithosphere only refers to the uppermost layers of the solid Earth (oceanic and continental crustal rocks and uppermost mantle).
Since space exploration began, it has been observed that the extent of the ionosphere or plasmasphere is highly variable, and often much larger than previously appreciated, at times extending to the boundaries of the Earth's magnetosphere or geomagnetosphere. This highly variable outer boundary of geogenic matter has been referred to as the "geopause", to suggest the relative scarcity of geogenic matter beyond it, where the solar wind dominates.
- ↑ Skinner, B: "The Dynamic Earth.", page 21. John Wiley & Sons, Inc, 2000 ISBN 0-471-16118-7
- ↑ Allaby,A. and Allaby, M. (eds). 2003. The Dictionary of Earth Sciences. Oxford University Press. Oxford University Press Inc., New York. 2nd edition. pg. 320.
- ↑ Siscoe, G.: "Aristotle on the Magnetosphere, Eos Transactions of Am. Geophys. Un., v.72, pp. 69-70, 1991.
- ↑ Moore, T.E. and D.C. Delcourt, The Geopause, Revs. Geophys., v32(2), p.175, 1995.