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