The Resource Depletion Theory claims that every non-renewable resource and every renewable resource coming from a finite storage place can be exhausted only by following the depletion curve. In the picture to below you can see how production levels for three real-life examples follow a bell shaped curve.
This theory has been first announced by M.K. Hubbert in 1956 for oil and other commodities, and it is known today as "peak oil theory". However, this theory has been confirmed through the oil production of many oil fields worldwide but is still denied by many scientists and economic leaders today.
The "Resource Depletion Theory" is a broader more simplified approach of that same concept of M.K. Hubbert. Studying the diagrams above should reveal to the reader that the concept of depleting resources is universal and a simple matter of mathematics and common sense.