ABSTRACT
The critical zone is "the heterogeneous, near surface environment in which complex interactions involving rock, soil, water, air and living organislns regulate the natural habitat and determine the availability of life sustaining resources" 2001). The critical zone is an interfacial region of mass and energy flux comprising terrestrial, lacustrine, and Inarine components of the continental crust and is one of two prilnary loci of life on Earth and for Inost of human activity. The other major locus of life is the sun 2001). The critical zone is comprised of an an'ay of spatial scales, ranging from the atomic to the global, and temporal scales, ranging from seconds to eons. The physical, chemical, and biological processes within the critical zone mediate exchange of mass and energy which is required for biomass productivity, chelnical recycling, and water storage. The critical zone is the most heterogeneous and abstruse portion of the entire Earth 2001). However, we must understand the physical, chemical, and biological processes and reactions in the critical zone over a range of spatial and temporal scales if we are going to sustain the planet for human habitation (Hochella 2002). Processes within the critical zone can be divided into four categories. Each of these affects the other and includes: biologic activity, weathering, fluid transport, and near-surface tectonics.
