I first investigated the properties of an ORN by computer simulation. Recent advancements in geophysics have revealed a promising possibility that the first living organism emerged near the bottom of a small, long pore in a mineral (FeS) precipitate in the vicinity of a hydrothermal vent in a primitive deep sea. We can see from these studies how an ORN is formed. Various chemical substances discharged from hydrothermal vents are speculated to have diffused into such pores and reacted with each other, thus forming an ORN. Reaction products with relatively large sizes and, hence, small diffusion constants likely accumulated within such small, long pores. Therefore, an ORN could have been formed in such pores as a result of differences in the diffusion constants between the entering chemical (source) substances and the reaction products.