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- 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.
An abiogenic substance or process does not result from the present or past activity of living organisms. Abiogenic products may, e.g., be minerals, other inorganic compounds, as well as simple organic compounds (e.g. extraterrestrial methane, see also abiogenesis).
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