1. Decreasing degree of geologic assurance
Cumulative
Production
IDENTIFIED
UNDISCOVERED
Demonstrated
Inferred
Probability Range
Measured Indicated
Hypothetical Speculative
ECONOMIC
Reserves
MARGINALLY
Marginal Reserves
Marginal
SUB-
subeconomic resources
subeconomic
resources
Decreasing degree of feasibility
Decreasing degree of geologic assurance
Figure 3.1. Classification of mineral resources (U.S. Bureau of Mines and U.S. Geological Survey, Circular 831, 1980). Based on McKelvey’s classification system (McKelvey, V.E., “Mineral Resource Estimates and Public Policy”. American Scientist, 60, 1 (1972):

2. Figure 3.2. Biomass production as a function of time.
Time
Figure Biomass production as a function of time.

3. Figure 3.3. Recruitment as a function of biomass.
Recruitment (R)
Biomass (S)
Figure Recruitment as a function of biomass.

4. Source: United States Geological Survey (USGS)
Figure 3.4. Select raw materials consumption in the U.S.

5. Figure 3.5. U.S. energy consumption by fuel source.
Source: U.S. Energy Information Administration

6. Source. U.S. National Park Public Use Statistics Office
Figure 3.6. Recreation visits to U.S. national parks.

7. Table 3.1. Mineral reserves to extraction ratios MINERAL YEAR
1995
2000
2007
Copper 2 3
Gypsum 42 36 39
Phosphate Rock 28 26 40
Platinum-Group Metals 78
127 54
Crude Oil 10 12 13
Source: United States Geological Survey (USGS)

8. Source: U.S. Energy Information Administration
Figure 3.7. U.S. crude oil reserves.

9. Source: U.S. Energy Information Administration
Figure 3.8. Nominal and real retail gasoline price trends in the U.S.