First: since we can't go back in time - and since so little evidence from the early Earth remains - AND since we have never found another planet with life OR even another sample of life - our understanding of the "primordial soup" is very limited. This is an important read in terms of understanding what we can and can't know (and it's also a good overview of current theory). However, from everything we do know, abiogenesis seems to be a process that rapidly (geologically speaking) transforms an entire planetary landscape. So there is probably a unique interaction between geology, chemistry, and atmosphere that must occur for life to emerge. What is probably safe to say (at this point) is that the "primordial soup" of early life was based in large bodies of water around hydrothermal vents.