Where did the first living things on earth come from?
No-one really knows, but there are some theories...
When we think of life today, we mainly think of DNA and associated supporting proteins, but prior to DNA life may have taken the form of self-replicating RNA. This in turn may have come from some kind of life based on PAH's (polycyclic aromatic hydrocarbons). We have detected PAH's naturally occuring in space.
So perhaps the Earth was seeded with PAH's from space, which became part of the primordial soup from which life developed.
An alternative theory - called "panspermia" - is that life exists throughout the universe, having arisen shortly after the Big Bang. Then Earth would have been directly seeded with life from space - perhaps carried on meteorites.