The problems of synthesising complex molecules from simple has already been discussed in this module. Laboratory experiments of this type sometimes use the presence of other materials to physically assist a chemical reaction. One such agent is thought to be the surfaces of some minerals, where free electrons may be used to enable a reaction to take place. There is evidence to suggest that sulphide mineral surfaces are particularly useful in this respect. Hydrothermal vents contain an abundance of the sulphides of iron and of copper which would have been available in the early Earth to facilitate biosynthesis reactions.
Another great difficulty in synthesising complex organic molecules, such as RNA and DNA is the initiation of the self-replication process. An ingenious idea suggested by Cairns-Smith, formerly of the University of Glasgow, is that clay minerals play a part in the replication process. Clay minerals are not living, but have a chemical structure which is characterised by endless repetition and Cairns-Smith proposed that organic molecules might have 'learned' the idea of self-replication from clays. Clays are a common alteration product of ocean-floor basalt adjacent to hydrothermal vents and are formed by the degradation of basalt by the hydrothermal solutions.