Revised 24 May 2019

All forms of life are open systems that maintain a state of high order and organisation by feeding on a source of negative entropy - solar energy - which radiates from outside the global ecosystem. Sustainable stocks of energy available to humankind include net phytomass and biomass of other forms of life which are self-maintaining stocks so long as they are not over exploited. Humankind throughout history has utilised the flow of sustainable stocks of solar energy to produce exosomatic capital stock extensions of human bodies which support human life. Exosomatic capital stock for hunter-gatherers included clothing, shelter, and tools. Exosomatic capital stock for modern humankind includes buildings, plant, machinery, and energy converters.