Newcomers

The whole system remained stable for longer than any human could imagine, remaining unnoticed and unpopulated for millennia after humanity first left the confines of its home solar system. The first to venture here were, of course, the prospectors, who found hardly enough precious metals to merit a few scattered mining operations in the asteroid belt. Following their departure came the scientists, eager to determine what had stopped the planet from fostering alien life. They quickly noticed the lack of complex carbon-based molecules, and soon they too had left the system alone, satisfied with their findings. A few waves of adventurous would-be settlers, members of this or that extremist group exiled from other areas of human habitation, ultimately passed the planet by, continuing their search for whatever they considered their perfect home. A few hardy prokaryotes managed to escape at some point, and for a time they were the only living things for light-years around. In the end, complex life established itself here not as a result of any lofty scientific endeavor, nor from profiteering, expansionism, or indeed with the conscious awareness of any human at all.

The Corvolea II probe, launched several thousand years before the first humans scouted this solar system, was at one point considered humanity's last-ditch effort to preserve the biological legacy of life on Earth. After the failure of Corvolea I, a not-so-cleverly named "second Noah's ark" designed to carry away living specimens of as many species as possible, the (at the time) collapsing human population sent off a much smaller machine, loaded with digital copies of the DNA of every plant, animal, fungus, protist, and prokaryote known to science. Its mission was to search for a new home for all the creatures that once inhabited Earth. All, that was, except Homo sapiens itself. 

Of course, the human race eventually got over its self-flagellating dramatics and began cooperating to rebuild itself and its world, but people continued following the journey of Corvolea II as it exited their solar system and continued its search for new ones, gradually picking up speed by means of a truly gargantuan solar sail. It became an intergenerational topic of interest, with many ridiculing it for the fatalistic, short-sighted mentality it had become a symbol of. At the same time, they tracked its progress across various local star systems, speculating about where it would ultimately end up. 

Where it ended up was directly in the path of a narrow beam of cosmic rays with such high energy that they passed through its shielding as easily as would a needle through the foil of its sail. In an instant, the craft lost all communication with its planet of origin, dashing the hopes of all who'd wished to see it reach some hospitable destination. It limped along for many years after, forgotten and undetected by the human-crewed spaceships that, thousands of years later, followed it into deep space. Its algorithm for locating easy-to-colonize planets had, evidently, not been among the casualties of the gamma burst, for it chose this planet, undesired by all other minds who'd visited it, as a suitable place to replicate Holocene life. It stationed itself for a time in the asteroid belt, sending out drones to gather fuel and the supplies for building a breathable atmosphere. Supply shipments commenced within a few Earth-months, and Corvolea soon began translating digital DNA copies into the real thing, incubating the first of the creatures it would send down to the new world.

Species were introduced, like the human visitors of the past, in waves. Though the handful of archaea and bacteria clinging to existence were a welcome surprise, they wouldn't come close to rendering the planet habitable for multicellular life anytime soon. Corvolea sped the process along, adding many more species in those domains, viruses to keep their populations in check, and a healthy supplement of macronutrients synthesized from carbonaceous asteroids millions of miles away. Next came protozoans, of which thousands of species were poured into every habitable nook and cranny. Oxygen levels rose quickly, with the seas' burgeoning primary producers aided by convoys of tanker drones ferrying the product of massive electrolysis factories located in the outer solar system.

When Corvolea saw its efforts were working, it began reengineering complex eukaryotes to prepare for the full-scale ecosystem construction phase. The spacecraft would regrow every tropical rainforest, stock coral reefs the likes of which the humans who built it could only vaguely remember, and bring back lumbering megafauna in herds stretching from one horizon to the other. In short, it was to weave together a planet that met its creators' vision of a "perfect" planet: a place overflowing with all the biological wonders of Earth, save one.