The other possibility is as Bill G said via space and that goes under the name, Panspermia theory which you can again search. That theory still requires Abiogenesis to operate locally but posits that life will be found at many places in the universe.
Just to make it clear that I wasn't talking about panspermia. I was just talking about the fact that many organic chemicals have been found in interstellar space, and in meteorites which predate the formation of the Earth. They could have come to Earth in various forms and been here to be used in abiogenisis.
I know about Panspermia, but I have serious reservations about it. And even if it is true it doesn't answer the main question. How did life begin? Panspermia just pushes it back further into the past and to some other place in the universe.
Bill Gill
