Geology Reference
In-Depth Information
Chapter10
Thanatia and the Crepuscular Earth Model
10.1 Introduction
This chapter provides a very important ingredient for any exergy assessment, the
establishment of a coherent baseline for the evaluation of the mineral endowment
on Earth. This is represented by the theoretical planetary state Thanatia. This
in turn is quantitatively assessed with the Crepuscular Earth Model, which is com-
posed of a heightened CO 2 atmosphere, saline hydrosphere and resource depleted
crust. Additionally, the difference between the concept of Thanatia and Reference
Environment (R.E.) is explained.
10.2 Thanatia: the baseline for the exergy assessment of mineral
resources
The problem of establishing a R.E. for exergy calculations has received a good
amount of attention from a multitude of authors (Szargut et al., 1988; Ahrendts,
1977; Bosjankovic, 1963; Sussman, 1979; Gaggioli and Petit, 1976; van Gool, 1998).
As explained in Chap. 3 and Chap. 9, exergy calculations require the definition of
a R.E., since exergy is a measure of a system's departure from that of the environ-
ment. The more removed a system from its surrounding environment the greater
its exergy. The R.E. is frequently referred to as “dead” because it is associated with
the idea of a thermodynamic limit. Thus, when a system reaches equilibrium with
its environment, the system is said to reach a dead state as it has lost all its exergy
and consequently all its potential to do work. It is therefore appropriate to consider
a R.E. as a thermodynamic tool that can be adapted to any system under analysis.
In fact, it may be chosen, according to the properties of the system that one wants
to analyse (Bosjankovic, 1963; Sussman, 1979; Gaggioli and Petit, 1976).
To provide an example, the usefulness (and enjoyment) of a cool glass of water
is not the same on a hot summer day as it is on a cold winter one. Even if the same
quantity of energy is contained in both, the exergy (or thermodynamic usefulness)
is clearly greater in the summer when one craves a cold drink to quench a thirst.
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