In this Let's-Read-and-Find-Out Science entry, readers learn that, as is true of the space shuttle, Earth is a space craft, speeding through the ether with its own life support systems, elegantly rigged out for recycling. Lauber (How Dinosaurs Came to Be, p. 533, etc.) gives each system a simple, thoughtful mulling over—how water gets from human stomachs back into the clouds, why all the available oxygen doesn't get used up, the role that the littlest creatures (beetles, mites, bacteria) play in the cosmic scheme. Crisp explanations—accompanied by Keller's sharp illustrations—make clear significant natural processes. The book closes with suggestions for poking about in old leaf piles to see Mother Nature at work and a reminder to take care of spaceship Earth. (Picture book/nonfiction. 5-9)