The Exergy of the Earth and its Mineral Resources - Thanatia: The Destiny of the Earth's Mineral Resources - page 332

11.2.4 The chemical exergy of the Earth

In Chap. 5 some of the physical properties of the Earth in its entirety that are
now required for chemical exergy calculations were described. To recap, the Earth
has a mass of around 5:98 10 24 kg (Beichner et al., 2000). Its relative mass
proportions of each of the spheres are: hydrosphere (0.023%), atmosphere (0.842
ppm), core (35.5%), mantle (67%), oceanic crust (0.072%) and continental crust
(0.36%) (Javoy, 1999). The upper layer of the latter constitutes approximately
50% of its whole mass (Yoder, 1995). Table 11.8 shows the standard chemical
exergy of the aforementioned layers and their collective sum 4 .

Table 11.8 The standard chemical exergy of the Earth's outer layers

MW, g/mol b 0 ch , kJ/mol B 0 ch , Gtoe

Layer Mass, kg

Atmosphere 5.04E+18 28.96 0.11 4.41E+02

Hydrosphere 1.38E+21 18.29 0.58 1.03E+06

Upper continental crust 1.08E+22 155.2 3.63 6.02E+06

SUM 7.05E+06

The results of Table 11.8 indicate that the standard chemical exergy of the
Earth's outer spheres is 7:05 10 6 Gtoe. This can be considered as a reasonable
estimate which is subject to updates, especially once the mineralogical composition
of the crust becomes better known, the Gibbs free energy of all substances is em-
pirically obtained and a more appropriate R.E. is found. That said, even in the
absence of precise data the order of magnitude is good enough to understand the
huge chemical exergy content of the Earth. Of all the layers, the upper continental
crust is that which is responsible for most of the exergy (85.4%), due to its greater
mass portion and specific exergy. Furthermore, although the relative proportion
of the atmosphere and hydrosphere is small compared to the whole, their chemical
exergies are also large: 4:4110 2 and 1:0310 6 Gtoe, respectively. And since the
Earth can be assumed to be a closed system in materials, this exergy can be seen
as a non-renewable reservoir of chemical substances.

11.3 The exergy of mineral resources

In the previous sections, the chemical exergy of the main substances that compose
the Earth was obtained. The topic from now on focuses on a very small part of
the Earth's constituents: the mineral resources, whereby, the average exergy of
the proven reserves of coal, oil and natural gas, as well as that of the main non-
fuel mineral reserves, reserve base and world resources (described in Chap. 6) is
obtained.

4 It is assumed that there is no mixing among the considered layers and hence the Gibbs free
energy and exergy of the mixture term is zero.