Amount used per year Years of economic if everyone consumed at U.S. rate Years of economic supply left if everyone consumed at U.S. rate Known economic Amount used Metal per year supply left reserves Titanium 750,000 7550 99.3 32,975 22.7 Copper 690,000 17,900 40,654 Nickel 74,000 2490 4562 Tin 4700 230 939 Tungsten 3500 71 314 Antimony 1800 163 542 Silver 520 26 152 Gold 54 2.8 3.6

Some metals are in such limited supply that, at today’s prices, they could be available to us for only a few more decades. After that, prices will rise as they become scarcer. The number of years of total availability (at all prices) depends on a number of factors: On the one hand, metals will be available longer if new deposits are discovered, new mining technologies are developed, or recycling efforts are improved. On the other hand, if our consumption of metals increases, the number of years we have left to use them will decrease. Currently the United States consumes metals at a much
higher per-person rate than the world does as a whole. If one goal of humanity is to lift the rest of the world up to U.S. living standards, then this will sharply increase pressures on mineral supplies. The chart shows currently known economically recoverable global reserves for several metals, together with the amount used per year (each figure in thousands of metric tons). For each metal, divide the reserves by the annual amount used to calculate the number of remaining years of supply at current prices. Enter the number of years in the fourth column. The fifth column shows the amount that the world would use if everyone in the world consumed the metal at the rate that Americans do. Now calculate the number years of supply left at current prices for each metal if the world were to consume the metals at the U.S. rate, and enter these values in the sixth column. 

Which of these eight metals will last the longest under
current economic conditions and at current rates of global
consumption? For which of these metals will economic
reserves be depleted fastest?