Terrestrial situations

Salts seem to be nearly as widespread as ice (though not as abundant) in the Solar System, being present on nearly every object where ice has also been observed and where indications of a watery past are in evidence (Enceladus is the key exception so far). There are very few instances (Venus is the most notable one) where salts occur on worlds where H2O is absent or nearly absent. This is a striking correlation, given the terrestrial situation of most evaporites, which are mostly associated with hot and arid areas of Earth. Even so, notable instances of ice-associated evaporites also occur on Earth. In detail, each world and the paragenesis of its salts tells a different story. The key point here is that in this Solar System, salts commonly are associated directly with ice. Hence, phase equilibria generally are described by FREZCHEM, even if on Earth some of the most important evaporite deposits were not formed in the presence of ice or icy-cold conditions. 

There is a general relationship between metal price and terrestrial concentration. Metals present at relatively high concentrations, in the earth s cmst, such as iron and aluminum, are the least expensive rare metals such as gold and platinum are the most valuable. This situation has existed for gold and silver valuation for centuries. The amount of silver in the earth s cmst is approximately 20 times that of gold, and the historical price ratio for gold and silver varied between 10 and 16 for over 3000 years. Since 1970 that price ratio has been strongly affected by market forces and investor speculation. 

There are some important situations in which a flux between two reservoirs is determined not only by the mass of the emitting reservoir but also by the mass of the receptor. Uptake of CO2, or indeed any other nutrient by a plant community depends also on the magnitude of its biomass because that determines the size of the surfaces where photosynthesis take place. Consider, for example, the uptake of atmospheric CO2 by terrestrial biota. A reasonable parameterization of this flux would be... 

In Europe the situation is radically different. Isotopic variations at the bottom end of the food web, brought about by differences in plant metabolism (C3, versus C4 and CAM), and origin of the fixed COj, (causing a systematic discrepancy between terrestrial and marine ecosystems) are generally absent. This leads to relatively small variations in ratios at the beginning of... 

As mentioned earlier (Figure 5.5), aldrin and heptachlor are rapidly metabolized to their respective epoxides (i.e., dieldrin and heptachlor epoxide) by most vertebrate species. These two stable toxic compounds are the most important residues of the three insecticides found in terrestrial or aquatic food chains. In soils and sediments, aldrin and heptachlor are epoxidized relatively slowly and, in contrast to the situation in biota, may reach significant levels (note, however, the difference between aldrin and dieldrin half-lives in soil shown in Table 5.8). The important point is that, after entering the food chain, they are quickly converted to their epoxides, which become the dominant residues. 

Among the terrestrial planets, the situation of the Earth is special. Its atmosphere (around 21% oxygen and 78% nitrogen by volume) is completely different from... 

Tjell, J.C., T.H. Christensen, and F. Bro-Rasmussen. 1983. Cadmium in soil and terrestrial biota with emphasis on the Danish situation. Ecotoxicol. Environ. Safely 7 122-140. 

Atmospheric transport of atrazine-contaminated aerosol particulates, dusts, and soils may contribute significantly to atrazine burdens of terrestrial and aquatic ecosystems. The annual atmospheric input of atrazine in rainfall to the Rhode River, Maryland, as one example, was estimated at 1016 mg/surface ha in 1977, and 97 mg/ha in 1978 (Wu 1981). A similar situation exists with fog water. When fog forms, exposed plant surfaces become saturated with liquid for the duration of the fog (Glotfelty et al. 1987). 

It may also be possible to hypothesize that aquatics will be of less interest in screening programs as aquatic environments do not expose plants to as great a diversity of pathogens and predators. It may be that terrestrial habitats present a more competitive situation that favors selection of a greater accumulation of diverse secondary metabolites with specific bioactivities, the exact kinds of molecules likely to be of interest in pharmaceutical screens. 

The organic geochemist encounters a quite different situation. Most organic products of organisms are thermodynamically unstable. When incorporated into sediments, they persist for long time spans because of the high degree of metastability inherent in carbon compounds under terrestrial environment conditions. The lack of equilibrium in the sedi-... 

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