There's a theory that says that life didn't even start on earth.

We found a bacteria that can survive being completely frozen, and can survive extremely high temperatures and high levels of radiation. We've also found Mars rock that may have contained microscopic bacteria fossils on Earth. Basically there's a good chance that the universe is filled with meteorites full of single-celled organisms are just waiting to crash some sort of planetary body where they can start dividing again.

3 billion years ago one of those meteorites hit Earth and that's why we're all here right now.