Epictetus, et al,
No one knows hw life (on Earth) started.
(COMMENT)
Life, as we define it, has an unknown origin. We understand that at a certain point, simple forms of life emerged. But no one knows if humanity traces back its origins to those few simple life forms, or if something else, off-world, was a trigger for the strand called humanity.
There are several theories. Some with evidence, and some with out. But the "idea" that the trigger came from off-world is neither more likely or less likely. Remember, everything on the planet is made of star dust. All the atom in our bodies came from the stars. So, whether it is home made soup (of life), or delivery, it all started out the exact same. There is simply insufficient evidence on either side, supporting any theory, to argue one way or the other with any confidence. It could even be the case that life on the planet is a composite of both types.
Most Respectfully,
R