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Published online by Cambridge University Press: 07 May 2025
Humankind is truly at a crossroads. It may either degenerate into oblivion destroying its abode, the Earth, or it may change course and sustain its civilization for the foreseeable future. The material that is available to humankind and all our co-inhabitants of the Earth is physically limited, and the energy that is usable for long is only that from the Sun. All other energy sources are exhaustible, and will not last long at the current rate of exploitation. Materials naturally available (or at least readily usable) are usually present in a relatively low-entropy state. Once such materials are processed, utilized and discarded/dispersed into the environment, their entropy is enormously increased. Then it is hardly possible to recover it in a low-entropy state. Hence, though they never disappear, such materials are non-renewable in practice. This writer has attempted to estimate the resource availability of major elements on the Earth and the anthropogenic exploitation rate (Ochiai, 2004).