From Mark Perry
"Bottom Line: Over a very long period of time (76 years), there has been a significant downward trend in the real prices of commodities (see red trend line in graph), and the decline in commodity prices has taken place during a period when the world population increased by more than three times, from 2 billion in 1934 to the current population of 7 billion in 2010."
This gets at concept that is very difficult for may to understand: As long as we have markets we will never "run out" of anything. The Stone Age didn't end for a lack of stones and the Bronze Age didn't end for a lack of bronze. The oil age will not end for a lack of oil.
As commodities become more scarce relative to demand, those who produce, extract, and process the commodities have a financial incentive to do their work more efficiently and cost effectively. (Recycling is included as one way to "produce" more.) Mineral or oil deposits that may once have been considered too difficult to obtain become practical because of technological innovation.
As any commodity begins to rise in price, one of two things happen. Either producers find ways to get more of it to market or buyers begin finding substitutes for the expensive commodity. In the short term (a few years) there can be disruptions but the long-term trend is ever downward. The chart above begins in the 1930s. But other charts I've seen going back to the 1860s show the same continuous trends.
The challenge is that too many tend to project present realities unaltered into the futre and see a world running of this or that in X many years. But markets and human adaptation ensure that almost nothing in the present can projected unaltered into the future.