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A 'biogenic substance' is a substance produced by life processes. It may be either constituents, or secretions, of
plants or animals.
'Examples'

★ Coal and oil are examples of constituents which have undergone changes over geologic time periods.

★ Chalk, and limestone are examples of secretions (marine animal shells) which are of geologic age.

★ Cotton and wood are biogenic constituents of contemporary origin.

★ Pearls, silk and ambergris are examples of secretions of contemporary origin.