The "RNA world" hypothesis claims that ancient organisms used RNA to carry out basic biological functions and only later evolved to use DNA and proteins (1). This hypothesis was supported by the discovery of ribozymes, RNA molecules that are able to catalyze chemical reactions in an enzymatic manner, much like proteins (2). Ribosomes are, in fact, ribozymes, and the finding that protein synthesis is carried out primarily by RNAs gave credence to the RNA world hypothesis (3). As both a storehouse of genetic information and a catalyst of metabolic reactions, RNA may have been the critical component that enabled the evolution of life as we know it.

Some of these early ribozymes must have acted as RNA replicases, capable of using neighboring RNA molecules as a template to create additional replicases. In a prebiotic pool lacking compartmentalization, however, there would be no selective advantage for an improved replicase; a better replicase will simply copy other replicases more efficiently, whether they are closely related or not. Compartmentalization is thus necessary to allow better replicases to preferentially grow in number and evolve (4). These compartmental boundaries were likely to have been formed by lipid bilayers that assembled spontaneously into vesicles in the prebiotic environment (5). There is evidence that shows that minerals, such as the clay montmorillonite, are capable of catalyzing both the polymerization of RNA as well as the conversion of lipid micelles into vesicles (6). Reactive substrates such as montmorillonite may well have given rise to simple protocells that were the precursors of all life on Earth.