I voted abiogenesis.

Panspermia can mean 2 things: That life started in space (e.g. inside a nebula or high orbit of exo-planet and floated into space) OR it started by abiogenesis ON ANOTHET PLANET and survived a flight through space to reach Earth and rain down (e.g. Earth life came from Mars by meteorite originating from Mars' surface).

I'm going to apply Occam's Razor now, and pick abiogenesis on Earth as the most likely scenario. The right ingredients were all there. Nothing on Earth seems to have PREVENTED life from starting here, so abiogenesis on Earth seems a more likely option opposed to extra-planetary abiogenesis + surviving space flight.

I'm not sure about the odds of life forming in space itself. Is there any reason to suspect that a nebula passed through our solar system 4 or 5 billion years ago and deposited proto-life on Earth? If not, then the odds of panspermia don't seem so good for that option.

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