Epilogue - Thanatia: The Destiny of the Earth's Mineral Resources - page 507

required are easily obtainable with adequate computer programmes. That said,
international agreements should be reached in order to update and complete both
data and indicators as well as improve interpretations and act accordingly. Further-
more, as exergy is an additive property, it is capable of integrating and aggregating
additional causes of variation including how substitution, recycling and nanotech-
nologies could positively improve the global management of mineral endowment.
Conversely, as this cost can easily be converted into monetary units, just by multi-
plying it by a previously agreed energy price, every country, company or mine could
use the annual variation of extraction costs to account for the attained depletion
level, as is shown for Australia in Sec. 13.4.
Finally, the proposed indicators complement others, especially cradle-to grave
ones as they close element cycles. Collectively they could provide an overall measure
of “unsustainability” and its yearly variation, which could in turn be used as a policy
lever.
17.3 Main outcomes of the thermodynamic assessment of the
mineral endowment
With the tools developed throughout this topic, the authors have undertaken a
quantitative evaluation of the mineral endowment on Earth. This was made possi-
ble with the information provided in Part 2, where the planet's geochemistry was
described, along with the resources that Man deems useful and the technological
processes necessary to convert such resources into commodities.
Accordingly, the calculations presented have served a threefold objective in the
obtainment of the Earth's mineral endowment: exergy values, exergy costs and
finally an analysis of the planet's exergy evolution: past, present and future.
17.3.1 Mineral endowment exergy
In order to have an insight as to the mineral wealth of mines, the authors have
obtained an approximate value of the chemical exergy of each of the outer layers
that compose the Earth, namely the atmosphere, hydrosphere and continental crust.
The following values were calculated: 4:410 2 , 1:010 6 and 6:010 6 , respectively.
Such figures provide an order of magnitude of the huge chemical wealth of the
planet. If, by way of contrast, one calculates the chemical exergy of non-renewable
resources, it becomes clear that concentrated stocks of minerals (fuels and non-fuels)
contribute only to a very small fraction of the Earth's total chemical exergy (around
0.01%). This indicates that although the whole crust is composed by minerals, they
are not all in practice recoverable, with only a tiny fraction potentially exploitable.
When turning to renewable resources it has been shown in Chap. 11 that there
are a large amount of diverse energy sources that exist but are not useable in their
entirety due to the limits of current technology. Thus with a feasible improvement to