I still lean towards something along the lines of The Miller-Urey experiment[0]. There are many very interesting theories[1].

But who is to say it isn't a combination of both? The question would be, from whence did the life on comets/extra-terrestrial bodies originate?

[0]https://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment

[1]https://en.wikipedia.org/wiki/Abiogenesis