The concept, called lithopanspermia, is probably best known from its appearances in science fiction: A space rock that delivers alien life to Earth is one of the genre’s most beloved tropes.
Did alien rocks bring life to Earth, or was it the other way around? Rather, is it Earth rocks bringing life to alien planets? We can’t rule out the possibility of life from Earth seeding an outer solar system moon.
“If the numbers were much lower than one, we’d assume this event is unlikely to have occurred since the origin of life on Earth. But one to ten impacts over the last several billion years tells us we can’t rule out the possibility of life from Earth seeding an outer solar system moon.”
Worth estimates an asteroid trip from Earth to an outer solar system moon would take at least three million years, and maybe closer to ten.
Apparently, asteroid debris released from planet Earth falls back to the surface all the time, raising the possibility of “Self-panspermia.” Were Earth to suffer an Armageddon-style asteroid impact or nuclear winter, orbiting space bacteria might just be able to re-seed the surface.
Perhaps we’ll never know for sure if alien rocks brought life to Earth, or if Earth has spawned life on other planets.