The Arcadians were a major posthuman political movement interested in remembering and guarding the human culture of pre-destruction Earth. They were often mistaken to be the dominant faction of the early posthuman era.
The Arcadians with the strongest bio-socio-psycho-emotional link to Earth were the self-termed "guardians". A significant portion of the guardians were members of the final generations of survivors from Earth. In a "ludicrous colonial throwback", (PROSE: The Book of the War) the Guardians set out on a 7 century voyage to the only planet with the same atmosphere and temperature as Earth, Refusis II, (TV: The Ark) to found a "new Earth". (PROSE: The Book of the War)
The Tenth Doctor once summarised the founding of a notable New Earth, "Soon as the Earth burns up, oh yeah, they get all nostalgic, big revival movement, but then find this place. Same size as Earth, same air, same orbit. Call goes out, the humans move in." (TV: New Earth)
Arcadians outside the guardian faction were satisfied to terraform or create worlds to be their new homes, leading to the founding of about 28,000 planets named "New Earth". (PROSE: The Book of the War) Hereafter was one such world terraformed to be Earth-like in the wake of the original Earth's loss. (PROSE: The Silent Stars Go By) Foyle's House of the Rising Sun was located on the most prosperous New Earth. (PROSE: The Book of the War)
Isolationist to the point of considering all the rest of posthumanity their enemies, the Arcadians eventually almost completely vanished from the universe, with The Book of the War suggesting they either ascended to a higher state of existence or died of boredom. (PROSE: The Book of the War)
After the extinction of their human creators over 100 generations after the evacuation of Earth, robots calling themselves "Guardians" protected the final archive of Earth culture, Hope, while they searched for Earth in the hope that the danger from solar flares was over and that they could repopulate the planet with clones made from "pure" human DNA. These Guardians destroyed their archive to prevent it from falling into the hands of human-descended beings they knew only as "the Other". (PROSE: Aliens and Predators)
Near the end of the universe, a group of ancient, inbred humans — who thought themselves "guardians of the universe's greatest culture" — awoke from cryogenic stasis in a secret underwater base near Hope, determined to reshape the planet Endpoint with a cloud seeding pod into a "new Earth". The Eighth Doctor helped steer these humans away from their idolisation of the past towards peacefully living with their contemporaries, the human-descended Endpointers. (PROSE: Hope)