1. Life on Earth appeared within a very short time from when the Earth cooled to the point where it was possible. This is suggestive of a high probability of abiogenesis compared to the life span of the Earth. It has been argued that anthropic reasoning may make this meaningless, but that is unknown.
2. We know that the organic molecules that make up life are produced in copious amounts in a variety of different circumstances, many of which would have been around in the early Earth.
3. Small strands of RNA can form quite naturally, and it's very, very easy for RNA to replicate in the right thermodynamic environment (consisting of repeated heating and cooling). Once you have replication, evolution takes over.
4. Lipid layers also form very readily within the right thermodynamic environment, and tend to form enclosed membranes. They also replicate naturally in the right conditions (but don't evolve without containing genetic material). These membranes are a boon for life because they concentrate the chemicals required for replication.
5. Various catalytic surfaces have been discovered that can accelerate the required chemical reactions dramatically.
No, not yet. But since our observations have been very strongly limited by selection effects due to our observing instruments, and since we've found so many so close, planets are apparently the norm rather than the exception.
