A turkey vulture spreads its wings in one of California's deserts. Even though desert is the dominant landscape of our solar system—with Mars shivering and Venus baking in aridity—the Earth has managed to keep the oceans that foster life. But with one third of our landmass arid, scientists warn we could tip our climate toward that of Mars or Venus.

(Text adapted from and photograph shot on assignment for, but not published in, The Desert," November 1979, National Geographic magazine)