After the earth dies, some 5 billion years from now, after it's burned to a crisp, or even swallowed by the Sun, there will be other worlds and stars and galaxies coming into being - and they will know nothing of a place once called Earth.
Carl SaganWe can make a similar examination, but with greater uncertainty, of the extraterrestrial hypothesis that holds that a wide range of UFOs viewed on the planet Earth are space vehicles from planets of other stars.
Carl SaganIt would be wryly interesting if in human history the cultivation of marijuana led generally to the invention of agriculture, and thereby to civilization.
Carl Sagan