Panspermia

Panspermia is a theory that suggests that life on Earth came from space. It suggests that things like bacteria, viruses, and other life forms can survive in space and travel from one planet to another. If an astronaut from Earth traveled to another planet in a spaceship, he would find bacteria and other living things that weren't from that planet but had come from somewhere else in space. The panspermia theory says that's how life on Earth began, when bacteria and other living things arrived from another place in space.