I've already read on a lot of theories concerning the origin of life. To an extent, some of these theories may be deemed to be reasonable and with scientific basis. One of the most common theories is that thh first life came from some proverbial soup of organic molecules, which eventually ended up in life originating in the seas. Another theory holds that there was no primordial soup. Rather, first life came from the energy sources hidden deep underground billions of years ago.
Now there is one theory that I can't help but find funny at times, because it seems to be the kind of material you see on your local sci-fi channel. This theory, called panspermia, holds that life on earth originate from seeds that were already pre-existing somewhere else in the universe. According to this theory, life on Earth may have originated from outer space and transported here billions of years ago. This theory also holds that the seeds of life may have also been transferred to other habitable places.
But how were the supposed seeds of life transferred? Different theories also come about, including radiation pressure, lithopanspermia, and deliberate targetting of the Earth. It's still actually very open to the imaginations of people, bounding already to science fiction.
Note that there hasn't been any scientific evidence to give credit to this hypothesis. It is the general belief that panspermia, especially in its interstellar form, is impossible because of the difficulty or rarity of chances of surviving in outer space. Now if the transfer was deliberate, then that is another issue altogether.
Of course more radical thinkers believe that our origins was actually made intentionally by aliens, whose goal was to propagate their species. Eventually, according to this another theory, human beings became far apart (judging from the physical appearance) from their alien ancestors due to evolution. Aliens, as we all know, is another complicated topic that we have no scientific evidence to prove.
As to what really originated life, we really cannot tell. My guess is that we really cannot tell even in the future.
