Geologic time factors determining

It is estimated that the earth s age is in the neighborhood of 4 to 7 billion years. These estimates are basically derived from carbon-14, potassium-40, uranium-235, and uranium-238 dating of earth rocks and meteorites. The meteorites give important data as to the age of our solar system. Geologic time is felt to be represented by the presence of rock intervals in the geologic column (layers of rock formations in vertical depth) or by the absence of equivalent rocks in correlative columns in adjacent locations [25,26]. The two basic factors that are used to determine geologic time are ... 

Whereas the degree of coaliflcation generally determines the rank of the coal, the process is not a series of regular, or straightforward, chemical changes. Indeed, complexity is the norm insofar as the metamorphosis of the plant debris relies not only on geological time but also on other physical factors, such as temperature and pressure. Thus, the occurrence of a multitude of different and complex chemical reactions (no matter how simple they appear on paper or how simply they occur in laboratory simulations) is inherent in the coaliflcation process. 

Deep geological disposal is the most favored solution for the permanent disposal of nuclear wastes with long half-lives. Although the locations of the burial places are selected with outmost care to avoid migration of the wastes in nature over a very long period of time, no barrier can be safe forever, so, numerous studies are in progress to determine the main factors that could cause leaks of radioactive nuclides. Soluble compounds in ground water are likely to play a major role in the release of actinides. 

Two important factors are suggested by this model. First, the concentration of a trace element in a particular mineral (like talc) formed in this manner depends upon many factors including the size and charge of the ion (which eflFect the partition coefficient), the composition of the aqueous solution, the minerals present in the intrusive (determines D ), and the time or extent of reaction. Since talcose rocks of similar composition can be formed by various different processes, the differences in any of the factors noted above would result in different trace element contents. Second, since the assumption that the partition coefficients for antigorite, talc, and tremolite are similar appears to be true, one would expect their trace element contents to be similar. This means that a series of soapstone samples collected from a particular geologic body might contain different amounts of these minerals but that they all would probably be very similar in trace element content despite differences in the bulk element composition of the samples. 

Another application of a geological type is that of dating lava flows (135). At the time of a volcanic eruption, hot lava removes any past thermoluminescence, and after the lava cools the natural radioactivity present in the environment irradiates the lava over a period of years. The thermoluminescence intensity can then be recorded to determine the age of the lava flow, a calculation based on a number of factors. 

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