You comment on the absence of "pre-biology" on Earth, but I think you're seeing it the wrong way.

Consider a haystack, gently rotting in the summer sun. Biological activity and breakdown of the tissues of the straw leads to warming of the haystack. Volatile gases are driven off. At some point, combustion begins. (It is quite common for compost heaps and haystacks to self-ignite). Imagine this as an analogue to the initiation of life (fire) from a pre-biological state (the volatile imbalance of the steaming haystack).

The result - fire (or life) consumes and destroys, or at least transforms beyond recognition, the unburned pre-fire (pre-life) state. We are left with a burning haystack, and no sign of the processes that led from a simple stack of cellulose to a flaming pyre.

In a similar way, the active chemistry of pre-life is forever destroyed on Earth by the transition to life. The spark of life has consumed the elements that permitted it, and it has moved on to bigger and better things. As scientists we can speculate about pre-life and model parts of the active chemistry of putative pre-life, but we have no hard evidence on Earth.

Perhaps if Mars did reach a pre-life or early life stage then became deep-frozen, there might be better evidence there of the early steps of life, but this is pure speculation.

I would refer the interested reader to Clifford Matthews' very interesting ideas about the origin of complex biology directly from HCN polymers ("Tholins"), in "Environmental Evolution" edited by Lynn Margulis et al. In contrast to the conventional "building block" model of increasing complexity of biology, he suggests that much of the complexity of protein/RNA interactions could have arisen directly from complex organic/polymer precursors in a tarry goo of HCN complexes.

Worth a read, and a think...