Geologic time scale

The magnesium ion is made available by migrating pore waters. If the process is continuous on a geologic time scale more and more Mg + is introduced to the system and the porosity reduces again. The rock has been over-dolomitised. 

Deuterium is abundant in and easily separated from water. There is enough deuterium on earth to provide power for geological time scales. In contrast, tritium is not available in nature, but can be produced from n+ lithium reactions (see Lithium and lithium compounds). Natural Hthium is exhaustible, but sufficient tritium can be provided from it until fusion energy production is efficient enough to involve only D-D reactions ... 

The sediment reservoir (1) represents all phosphorus in particulate form on the Earth s crust that is (1) not in the upper 60 cm of the soil and (2) not mineable. This includes unconsolidated marine and fresh water sediments and all sedimentary, metamorphic and volcanic rocks. The reason for this choice of compartmentalization has already been discussed. In particulate form, P is not readily available for utilization by plants. The upper 60 cm of the soil system represents the portion of the particulate P that can be transported relatively quickly to other reservoirs or solubilized by biological uptake. The sediment reservoir, on the other hand, represents the particulate P that is transported primarily on geologic time scales. 

While these calculations provide information about the ultimate equilibrium conditions, redox reactions are often slow on human time scales, and sometimes even on geological time scales. Furthermore, the reactions in natural systems are complex and may be catalyzed or inhibited by the solids or trace constituents present. There is a dearth of information on the kinetics of redox reactions in such systems, but it is clear that many chemical species commonly found in environmental samples would not be present if equilibrium were attained. Furthermore, the conditions at equilibrium depend on the concentration of other species in the system, many of which are difficult or impossible to determine analytically. Morgan and Stone (1985) reviewed the kinetics of many environmentally important reactions and pointed out that determination of whether an equilibrium model is appropriate in a given situation depends on the relative time constants of the chemical reactions of interest and the physical processes governing the movement of material through the system. This point is discussed in some detail in Section 15.3.8. In the absence of detailed information with which to evaluate these time constants, chemical analysis for metals in each of their oxidation states, rather than equilibrium calculations, must be conducted to evaluate the current state of a system and the biological or geochemical importance of the metals it contains. 

Source From Palmer, A. R. and J. Geissman (1999). 1999 Geologic Time Scale. The Geological Society of America. 

Since the water movement will be very slow compared with the rate at which the wastes dissolve, we are concerned first and foremost with equilibrium solubility. Also, if only to relate behaviour on the geological time scale to that on the laboratory time scale, we will need to know about the mechanisms and kinetics of dissolution and leaching. The waste forms envisaged at present are glass blocks containing separated fission products and residual actinides fused into the glass and, alternatively, the uranium dioxide matrix of the used fuel containing unseparated fission products and plutonium. In the... 

Ceramicrete cures to create final waste forms that are analogs of naturally occurring phosphate minerals. These minerals have been shown to be relatively insoluble over geologic time scales. The final waste form is stronger than typical room temperature, hydraulic cements and performs in the manner of high-temperature fused ceramics. The technology has been evaluated in bench-and operational-scale tests on contaminated wastewater, sedimenL ash, and mixed wastes. 

It is clear that the disposal of HLNW requires a high level of effective isolation for geological time-scales. In this context deep geological disposal has arisen as the most accepted option and there are already operational repositories of this type (waste isolation pilot plant, WIPP) in the USA, and in Finland and Sweden the plans are well advanced for the siting and construction of such facilities. 

Hence, as a continuation of the radiolytic oxidation scheme previously presented, we propose that the alteration of U02 in geological time-scales proceeds as follows full oxidation of the U02 surface to U(VI) oxyhydroxides that would include Ca and/or K+ as accompanying cations ... 

We now know these predictions were wrong, in part. While we believe there are a group of superheavy nuclei whose half-lives are relatively long compared to lower Z elements, we do not believe they form an island of stability. Rather, we picture them as a continuation of the peninsula of known nuclei (Fig. 15.1 lb). We also believe that their half-lives are short compared to geologic time scales. Therefore, they do not exist in nature. The most stable of the superheavy nuclei, those with Z = 112, N 184, are predicted to decay by a-particle emission with half-lives of 20 days. 

Many diverse processes are involved in the transformation of the elements and their compounds in the Earth. Some of the pathways observed are shown in Figure 1, a version of the so-called geochemical cycle . This cycle is very much simplified and is not a closed one. It may also be short-circuited and indicated processes may be very fast on the geological time scale, or, more often as not, occupy very lengthy periods, amounting in some cases to billions of years. 

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