Thomas Sowell, Basic Economics, towards the end of Chapter 12 Investment and Speculation, starting with paragraph Natural Resources.
here are some excerpts:
Present value profoundly affects the discovery and use of natural resources. There may be enough oil underground to last for centuries, but its present value determines how much it pays anyone to discover-and that may be no more than enough to last for a dozen or so years. A failure to understand this basic economic reality has led to numerous false predictions that we were "running out" of petroleum, coal, or some other natural resource. ...... How much of any natural resource is known to exist depends on how much it costs to know. Oil exploration, for example, is very costly. This includes not only the costs of geological exploration but also the costs of repeatedly drilling expensive dry holes before striking oil. As these costs mount up while more and more oil is being discovered, the growing abundance of known supplies of it reduces its price through supply and demand. Eventually the point is reached where the cost per barrel of finding more oil exceeds the present value per barrel of the oil you are likely to find. At that point, it no longer pays to keep exploring. Depending on a number of circumstances, the total amount of oil discovered at that point may be no more than the 13 years' supply which led to dire predictions that we were running out. ...
... Sometimes the known reserves of a natural resource seem especially small because the amount available at currently feasible costs is in fact nearing exhaustion. There may be vast amounts available at a slightly higher cost of extraction, but these additional amounts will of course not be touched until the amount available at a lower cost is exhausted. For example, so long as there were coal deposits available on top of the ground, no one was going to the expense of digging even a few feet into the earth to get more, because the higher-cost coal underground could not compete in the marketplace with the cheaper coal on the surface. During the interim, someone could should an alarm that were are "running out" of coal that is "economically feasible" to use, coal that can be gotten without "prohibitive costs." But again, the whole purpose of prices is to be prohibitive. In this case, that prohibition prevented more costly resources from being used needlessly, so long as there were less costly sources of the same resource available. This is just one of the ways in which prices contribute to economic efficiency.