What is sure is that life had a progress simple forms to complex forms,
that early life was simple but powerful enough to change the earth's
atmosphere's composition, so making different life possible;
we also know that the evolution pattern was not in (so to say) a straight line;
we also know that a 'perfect form of life' in an evolving environment would lead to death in the long run, as differentiation and therefore imperfection is the strategy of evolution; the mechanism of life transmission (i.e. characters replication) is very well known.
What is not clear, as it has never been observed in nature, neither done in an experiment is the critical passage from non-life to life; I truly believe that this happened, maybe in several millions occasions and only once in a while the life
was also capable of replicating, therefore joining the destiny of its host planet.
I also think that it is not 'what I think' that matters, but what 'science knows'.
In other words, would you ever ask:
"what do you think: does oxygen combine with hydrogen ?"
you will ask:
"what do you know: does oxygen combine with hydrogen ?"
The problem is that (at least to my knowledge), nobody really knows!
So, let's wait and do your best to find a piece of the answer, and hope to reach a complete answer before that dear yellow star in the day sky runs out of fuel.