If civilization still exists on planet earth in a billion years, what materials can those up to that time have used?
Lasting civilizations can use only materials
- for which closed cycles or loops exist (such as carbon, water, oxygen, hydrogen, hydrocarbons, nitrogen), or
- that can be regained from the environment economically to form forced cycles before they reach harmful concentrations, or
- that (if available from outside) can accumulate in ever increasing concentrations in the environment/biosphere without negative effect on life and civilization, and
- that exist in the biosphere or can be brought there and can be concentrated by economical means (see Ugo Bardi's discussion of the cost of obtaining useful materials on The Oil Drum, see also entropy)
Those that nature recycles before dangerous concentrations accumulate could be used indefinitely in civilizations. Carbon and hydrocarbon based materials, many of which qualify, have varied properties: e.g., diamond, plastics, and materials such as nanotubes that might be turned into semiconductors as well as living organisms.
For a lot of other materials e.g., metals or doted semiconductors recycling in a current sense is incomplete and no natural cycles are known. Even a modest wear or oxidation of such materials would eventually result in concentrations in the environment to which life would have to adapt, which may or may not be possible in the available time. Lasting civilizations could use such materials only if they posess and employ economical ways to remove these traces from the environment to keep the concentrations from exceeding harmful levels. In this way new, technically closed, but complete cycles would exist. For many materials we widely use today, such as aluminum or nickel, possibly even iron, we do not yet posess economical removal technologies from the environment at low concentrations. Such cycles may or may not be feasible. E.g., nanotechnologies might close the loops, but no civilization could rely on solutions it doesn't know will work. For a lot of materials this issue is not a concern on a horizon of centuries and would need to be solved in the long run, but for many substances it is unknown which levels are harmless and it is safe to switch to materials that can continue sooner rather than later.