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Published online by Cambridge University Press: 25 May 2016
A cyclic evolutionary picture is presented which follows the sources and nature of organics from interstellar space to comets. The three major organic components discussed are the grain mantles, the carbonaceous particles responsible for the 216 nm hump in the extinction, and the large molecules/small particles polycyclic aromatic hydrocarbons (PAHs). The variability in the oxygen and hydrogen abundances relative to carbon is followed.