The human world is - or rather was - Earth in 2025. A supposedly 'accidental' nuclear launch triggered a full out nuclear war, which shattered the planet within 24 hours. The tectonic plates were so rattled by the force and placement of the explosions that they lost cohesion entirely and drifted away into space. Anyone and everyone on the planet who was not killed by nuclear explosions, was killed by the sudden dispursal of the atmosphere.