The whole financial system is only available because of the energy humans are able to appropriate. We could not build bank buildings, or make coins, or have enough extra time for people to learn how to set up bookkeeping accounts, if humans didn’t have supplemental energy of some sort–not necessarily fossil fuels, but enough to “win” over the contest with animals.
I would argue that “money” should be included in the list of things that are not sustainable over the long run. It is a function of the extra energy we have gained that have allowed us to grow bigger brains, have language, and set up a civilization that animals were not able to do. - Gail Tverberg