One of the problems of abiotic and pre-biotic synthesis is that the Earth's early atmosphere was carbon dioxide-rich, that is, it was oxidising. Experimental studies, such as the lightning discharge experiment of Miller and Urey, require a mix of gases or fluids which is much less oxygen-rich than that expected in the Earth's primitive atmosphere in order to synthesis amino acids and the like. One possible resolution of this paradox is that the process of organic synthesis did not take place at the Earth's surface in a primitive oxidising atmosphere, but rather took place in an environment which was reducing (more hydrogen-rich). The evidence from modern hydrothermal vents is that the solutions which are vented onto the ocean floor are alkaline and reducing — see http://www.gla.ac.uk/projects/originoflife/html/2001/index.htm (select 'critical aspects' and then Fig. 1).
It is possible therefore that early hydrothermal vents supplied the appropriate fluids for the synthesis of the amino acids necessary for the formation of RNA and DNA.