Nature

"People have a funny habit of taking as 'natural' whatever they are used to—but there hasn't been any 'natural' environment, the way they mean it, since men climbed down out of trees."

"Wherever Man has mass and energy to work with and enough savy to know how to manipulate them, he can create any environment he needs."

Robert A. Heinlein, Farmer in the Sky, 1951. Sample chapters now available here.