The Exergy Evolution of Mineral Wealth - Thanatia: The Destiny of the Earth's Mineral Resources - page 395

following an exponential-like behaviour. Exergy degradation velocity subsequently
increased from around 10 Mtoe/yr at the beginning of the timeframe, until almost
reaching 60 Mtoe/yr in 1968.
The appearance of significant reserves of oil and natural gas (cleaner and easier to
handle fuels than coal), led to an important drop in coal production in the beginning
of the second period (see Fig. 13.27). Nevertheless, the abundance of national coal
stocks, together with the foreseeable depletion of oil, has since provoked further coal
extraction. Meanwhile, iron has gained prominence especially since the beginning
of the 20th century, exceeding the production of oil and natural gas in exergy terms
and reaching extraction figures comparable to those of coal (see Fig. 13.28).

600,000

B*, ktoe

500,000

400,000

Coal

300,000

200,000

N.G.

Oil

100,000

Iron

0

Other metals Iron Oil N.G. Coal

Fig. 13.27 Natural bonus depletion of the main fuel and non-fuel minerals in Australia from 1969
to 2008

B*, %

100

90

Coal

80

70

60

50

40

30

Oil

20

Iron

10

N.G .

Other metals

0

1914 1924 1934 1944 1954 1964 1974 1984 1994 2004

Year

Other metals Iron Oil N.G. Coal

Fig. 13.28 Relative contribution of the extraction of fuel and non-fuel minerals to the global
natural bonus degradation of Australia from 1914 to 2008