The hypothesis that life on Earth did not originate here, arriving as microbes on meteorites, spores on comet dust, or, in the boldest version, a payload deliberately seeded.
Documented
Arrhenius, Hoyle, and the survival data
Documented: Arrhenius (1903) proposed radiation pressure pushing spores between worlds; Hoyle and Wickramasinghe (1981) argued comets deliver microbes continuously; Crick and Orgel (1973) published directed panspermia, seeding by a prior civilization, as a serious option. The supporting data are real: some bacteria survive years in space exposure, meteorites travel between Mars and Earth, and organic molecules rain down constantly. Nothing documented says any of it delivered life.
Assessment: Documented as a legitimate research program with a cargo cult problem: transport is proven, the passenger is not. Every component exists; the journey has never been shown to happen.
Stories
We are the aliens
The folk version is irresistible symmetry: the ancient astronaut theory turned inward, humanity itself as the colony, our legends of sky-gods as garbled memory of the seeding. It retrofits every creation myth with a cargo hatch and flatters the species with extraterrestrial ancestry.
Assessment: Documented as mythology recycling the hypothesis. The myths predate the microbiology by millennia; the retrofit is ours. Filed beside Ancient Astronauts, same emotional engine, better vocabulary.
Interesting claims
The speed problem it was built for
The interesting claim is the honest motive: life appears on Earth suspiciously fast after the planet cooled, and the jump from chemistry to self-replication is the widest unexplained gap in science. Panspermia widens the runway by the whole galaxy's age. Directed panspermia sharpens it: Crick argued life's optimization smells designed, and his Nobel did not make that checkable.
Assessment: Documented as a solution to a genuine anomaly, and documented as unfalsifiable in its strong form. It exports the miracle rather than explaining it, which its own authors admitted. The gap it fills is real; the filling remains a hypothesis riding on cargo cult logic, respectable edition.
Sources and further reading
Arrhenius, Worlds in the Making (English edition, 1908), the original proposal
Hoyle and Wickramasinghe, Evolution from Space (1981)
Crick and Orgel, Directed Panspermia, Icarus (1973)
EXPOSE and tanpopo mission results, bacteria surviving space exposure
Mars meteorite transfer literature, the documented shipping route
Worth asking
If we are the descendants of travelers, does the question of where life began get easier, or does it just leave town?