Rocks for the long run  

The Economist has a look at long term commodity price trends - Rocks for the long run.

Long-run rises have been most pronounced for commodities that are “in the ground”, like minerals and natural gas. Energy commodities especially have boomed, soaring by roughly 300% since 1950. Prices of precious metals have also risen, as have industrial ingredients like iron ore. In contrast, prices for resources that can be grown have trended downwards (see chart). The inflation-adjusted prices of rice, corn and wheat are lower now than they were in 1950. Although the global population is 2.8 times above its 1950 level, world grain production is 3.6 times higher.