 What happened to Earth?
The ancient rule was sink or swim—swim in the miasma of a planet without spaceflight, or sink to utter destruction! [Transcriber's Note: This etext was produced from Worlds of If Science Fiction, July 1963. The planet chosen for our Trial was called Tintera. The last contact the Ship had had with it—and we were the ones who dropped them—was almost 150 years ago. Planets make me feel wretched. A planet is all right for a Mud-eater, but not for me. We have a place in the Ship like that—the Third Level—but it's only a thousand square miles and any time it gets on your nerves you can go up a level or down a level and be back in civilization. The ship lifted impersonally away from Ninc and me like a rising bird, and in just a moment it was gone. It was narrow and made of sand spread over a hard base. One of the smartest moves in history was to include horses when they dropped the colonies. I say "they" because, while we did the actual dropping, the idea originated with the whole evac plan back on Earth. One of the eight, as well as the two that were being built then, went up with everything else in the Solar System in 2041. I don't know how many of those planets had animals that could have been substituted but, even if they had, they would have had to be domesticated from scratch.
 Overpopulation caused a war
 People divided into small, vicious colonies  Overpopulation caused a war  People discovered more planets and chose to move  Everyone chose to live in space