So, the whole astronomy thing made me realize that I should make a master time traveler’s timeline first, which made me realize: the world is only human-habitable for about 1 billion of its 11-billion year existence! Before about 500 million years ago, there’s nothing to eat. About 500 million years from now, the sun will be too hot for human life (not just because of the greenhouse effect, but because it’ll be expanding and burning hotter.)

The image above is a kind of wireframe I’m putting together. Click on it to see a bigger version. I’m sure that I’ve made some errors, but I hope a geologist will straighten me out.