We briefly review the `RNA world' model for the origin of life,
and construct a model for its formation from prebiotic circumstances.
We describe, and then generalise, an existing model for polymerisation;
applying it to the formation of cell-like structures (micelles),
and then to describe the catatlytic properties of RNA polymerisation.
The model is then analysed showing how it predicts the growth of
long chains of RNA, and the formation of distinct `species'.