All the energy in the world would be of no avail if the nutrients required by life and the materials required by commerce are not continuously fed into the ecosystem or recycled within the ecosystem, or both. The interdependence of energy follow and material cycling is shown in post and the basic principles of nutrient cycling in the biosphere were discussed in post. The point was also made that as man depletes the reservoir storage bins, recycling not only becomes necessary, but some of the energy flow has to be diverted from productive processes (that is, new growth) to power the recycle process. Post provides an overview of three alternate depletion patterns for minerals such as iron, copper, aluminum, and so on, required in huge quantities by industrialized civilization. A one – way pastern of unrestricted mining, use, and throwaway is projected to lead to a boom and bust, as shown by curve a. some key metals, such as copper, could be ‘’mined out’’ by the year 2000. Depletion time could be extended by partial recline and less wasteful use, as shown by curve b. efficient recycle, including the necessary energy allocation, combined with stringent conservation and substitutions (switching to a more abundant material whenever possible) can extend the mineral depletion curve substantially (curve c). it remains to be seen whether mankind will, or can, make a choice between these options, or whether mankind will, or can, make a choice between these options, or whether events will force some other choice. As with fossil – fuel energy the total amount of minerals in the earth’s crust (and in sea water) is very large, but as the concentrated, easily mined supplies are dispersed, procurement becomes increasingly costly both in a monetary sense and in terms of ill effects on the environment. For a comprehensive review see the national academy’s report, resources and man, edited by cloud (1969).