Selected Geochemical Processes

In physical chemistry, the world is divided in two parts the system, containing the portion of the world of particular interest, and the surroundings, comprising the region ontside the system (Atkins and de Paula 2002). A geochemical system is an open system that may be studied within two basic frameworks  

Thermodynamic system, which is a state of equilibrinm where environmental parameters, snch as pressure and temperature, are imposed on the bulk composition of the system. This approach is nsed to predict the system stability and the impact of changing environmental conditions. 

Kinetic system, wherein the pathways along the system are moving toward some state of local equilibrium, which in tnm determines the rate of change along the pathway. In the context of a kinetic approach, which is relevant to geochemical processes, dissolntion-precipitation, exchange-adsorption, oxidation-reduction, vaporization, and formation of new phases, are discussed here. 

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Obviously since the products of the geochemical processes contain sulfur and carbon, sources for these elements must be considered but the selection of experimental substrates representing them will await prior chemical process analysis. The result of such an analysis that is relevant to the geosynthesis of compounds from polysulfide aianion and conjugated ene carbonyls will be reviewed briefly later. 

Copper was selected as the first metal for which to attempt to optimize the shipboard analyses because considerable information is available about the marine chemistry of copper, and because this new analytical capability would greatly enhance our ability to study copper in the ocean. The concentration of copper in the ocean varies from 0.5 to 5 nmol/kg in response to biological and geochemical processes (Table I). The chemical speciation of copper has received considerable attention because the biological effects of copper depend on its chemical form (i-3). The principal forms of copper include inorganic complexes such as CUCO3, CuHCO , CuOH, and organically bound copper (4, 5). 

Maes, A., and A. Cremers. 1986. Highly selective ion exchange in clay minerals and zeolites, p. 254-295. In J.A. Davis and K.F. Hayes (ed.) Geochemical processes at mineral surfaces. ACS Symp. Serv. no. 323, ACS, Washington DC. 

Clearly, the role of zooplankton in sedimentation of material is of great interest beyond biology (for example, 69), and there are interesting questions concerning the effects of the behavior of organisms on geochemical processes. For example, work on particulate radionuclides indicates that carbonate is sedimented in larger (or at least faster sink-ing) particles than is iron (70) one would like to know whether selective... 

The synthesis of RNA in extant biology, however, still relies upon the participation of proteins. The protein-fiTee de novo synthesis of RNA in a prebiotic reaction has yet to be demonstrated after several decades of effort (5). Many researchers have therefore concluded that RNA was not the first informational polymer of life. Rather, RNA was preceded by an RNA-Me polymer, or several generations of polymers, termed proto-RNAs, that were stracturally and functionally similar to RNA, but easier to assemble. Proto-RNA could have been comprised of different bases, sugars, and hnking molecules that were assembled through more thermodynamically and kinetically accessible pathways. Without the constraints of the current four RNA bases, ribose, and phosphate for the construction of an informational polymer, the possible composition of proto-RNAs seems limitless. However, tte existence of putative monomer units in the prebiotic chemical inventory for the assembly of proto-RNA would have been dictated by astro- and geochemical processes, paring down the set of molecules from which nature could select. 

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