Zombie City: an apocalypse story

It is the year 4,000. Humans have long ago left Earth for other, better planets. Still- several thousand humans still live there. Or rather, lived. In an attempt to salvage Earth (decades of pollution have steadily worn down it's atmosphere) scientists created a mutant human classified as a Z0M-B or Zombie. Now not only is the earth destabilizing, but more than half of the population has been killed or infected and become Zombies. You are part of a rescue group sent to save as many people and as much technology as possible- before Earth's atmosphere destabilizes, or the Zombies take over- whichever comes first (: