- Coal and oil are possible examples of constituents which may have undergone changes over geologic time periods.
- Chalk and limestone are examples of secretions (marine animal shells) which are of geologic age.
- grass and wood are biogenic constituents of contemporary origin.
- Pearls, silk and ambergris are examples of secretions of contemporary origin.
Carbon, from using biogenic and non-biogenic fuels, has implications for estimating the efficiency and environmental benefits of waste-to-energy incineration processes.
- Hogg, Dr. Dominic (2006) A Changing Climate for Energy from Waste? Final Report for Friends of the Earth