The Earth’s Critical Zone (CZ) is defined as "the heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air, and living organisms regulate the natural habitat and determine the availability of life-sustaining resources ".
It is not difficult to understand that studying it will be one of the most intriguing topics of the next years. Well beyond the actual way ecohydrology has arrived.
From Quijano and Ling, I simply copy:
"The CZ is the result of complex interactions of physical, chemical, and biological processes that have taken place over an evolutionary time scale . These interactions have been driven by energy, mass, entropy, and information fluxes, and the result is heterogeneous but organized structures that regulate the flow of energy down the gradients of various kinds [2,3]. "
Do not have very much to add right know (but studying it is one of the original motivation of GEOtop, at larger scales of JGrass-NewAGE). Thermodynamics plays a fundamental role in it - see also here, which makes it even more interesting to me).
Lin, H. Earth’s Critical Zone and hydropedology: Concepts, characteristics, and advances. Hydrol. Earth Syst. Sci. 2010, 14, 25–45.
Quijano, J., & Lin, H,. Entropy in the Critical Zone: A Comprehensive Review. Entropy, 16(6), 2014 , 3482–3536. doi:10.3390/e16063482
Rasmussen, C.; Troch, P.A.; Chorover, J.; Brooks, P.; Pelletier, J.; Huxman, T.E. An open system framework for integrating critical zone structure and function. Biogeochemistry 2011, 102, 15–29.