Xoanon is in fact a sentient spaceship's computer which the Doctor tried to repair years earlier by mentally joining with it. The computer's personality conflicted with the Doctor's, and it went insane. It separated the Survey Team from the Technicians, both groups eventually forgetting their true origins and worshipping the computer as a god. The Doctor wipes his personality from Xoanon before it can destroy the planet. A female warrior of the Sevateem tribe, Leela, joins the Doctor on his journeys.
Date is conjecture.
However, once they begin collecting the anti-matter, members of the expedition are killed off one at a time, the moisture completely removed from their bodies. In addition, one of the Morestrans, Professor Sorenson, has become infected by the anti-matter, and is mutating and killing the rest of the crew. The Doctor returns the anti-matter to its rightful place, returning Sorenson to normal and allowing the Morestran ship to leave. After returning to his own planet, Professor Sorenson begins to examine the possibility of using the energy generated by planetary motion as an alternative energy source for his people. In an alternate timeline where the Earth has been consumed by millennia of industrial waste, mankind has evolved into the blood-devouring Haemovores, led by the Ancient One.