[pdonis]

Life didn't start as cells. It started as "naked" self-replicating molecules with no supporting infrastructure. Think a virus without its protective protein coat. Cells only came along much later, because they are much harder to evolve.

We already know that an energy input, such as solar energy, to a large collection of simple molecules like methane and ammonia can produce the building blocks of life: amino acids and nucleotides. Once a short chain of nucleotides is formed, it will (slowly) replicate itself by attracting other nucleotides in the environment. That's all the original "life" on Earth consisted of. The simple chains of nucleotides were both "factory" and "information".

We don't know all the specific steps that life took between those first simple replicators and cells. We may never know for sure because data left over from that time is so sparse. But that's not the same as not having a viable theory. We have that.

[pfdietz]

That's a good story, but is there any evidence for it?

We know simple building blocks can be created, in low concentrations, with large amounts of other components that don't end up in life. The concentration of any given chemical in this mix is exponentially dependent on its complexity. The "once a short chain is formed, it will (slowly) replicate" is entirely unsupported by experiment. Indeed, it's difficult to see how it could work, when it's replicating in a soup loaded with junk monomers.