Geology Reference
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Exergy
Technosphere
Current Earth with
mineral deposits
Earth's evolution
Thanatia
Zero Exergy, R.E.
Fig. 10.5
Graphical representation of Thanatia's exergy with respect to the reference environment
Henceforth, one must distinguish between the concepts of “exergy” and “exergy
resource”. Exergy is conventionally calculated from a thermodynamic R.E. In con-
trast, an exergy resource is calculated from Thanatia as a baseline. Thanatia in-
volves the choosing of a reference barerock from which a material could be extracted
as an alternative from their current mineral source. This conceptual complexity can
be solved through a minor calculation, since exergy is an additive property. Thus
an exergy resource is obtained as the exergy of the material minus that of the
corresponding barerock constituting Thanatia.
Fig. 10.5 shows a graphical representation of the exergy of Thanatia and the
current state of the Earth with respect to the reference environment. When minerals
are extracted and refined, one is in fact increasing the exergy of the produced
raw materials used in the technosphere. This is however done at the expense of
additional resources (such as fossil fuels), thereby depleting the mineral deposits
from which they stem. As a consequence, the Earth gradually loses exergy and
approximates to Thanatia.
10.5 Summary of the chapter
The reader has seen in this chapter that the exergy of any substance is always
associated to a baseline. The conditions of which determine the exergy content of
a given system and thus careful selection of an adequate and appropriate reference
is of paramount importance.
The authors have thus presented an estimation of a suitable baseline, referred
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