Cosmic rays and aggressive environments don’t kill microorganisms; they even maintain an active metabolism that “heals” mutations. This gives rise to the hypothesis of reverse panspermia: terrestrial microorganisms could “conquer” space and become the origin of life on other planets. On the other hand, early life on Earth functioned in conditions so different from modern ones that they could seem almost alien. Studying these systems helps us understand not only where life might exist, but also what it might be like.