The differing patterns of molecular abundances in organisms are fundamental to the understanding of the biomolecular palaeontological record. All organisms contain DNA, RNA, protein, polysaccharides and lipid components, together with glycolipids, lipopolysaccharides and other complex molecules. Certain biopolymers, however, are restricted in their distributions; for example, lignin, cutin and sporopollenin are found only in terrestrial plants. The detailed chemical structures, namely the bond types present and their precise intramolecular environments, determine resistance to degradation. Observations of biomolecular preservation are compared with predictions based on chemical structure and on conditions encountered during decay.