Where Are They?; July 2000; Scientific American Magazine; by Crawford, side bar by LePage; 6 Page(s)

How common are other civilizations in the universe? This question has fascinated humanity for centuries, and although we still have no definitive answer, a number of recent developments have brought it once again to the fore. Chief among these is the confirmation, after a long wait and several false starts, that planets exist outside our solar system.

How common are other civilizations in the universe? This question has fascinated humanity for centuries, and although we still have no definitive answer, a number of recent developments have brought it once again to the fore. Chief among these is the confirmation, after a long wait and several false starts, that planets exist outside our solar system. Over the past five years more than three dozen stars like the sun have been found to have Jupiter-mass planets. And even though astronomers have found no Earth-like planets so far, we can now be fairly confident that they also will be plentiful. To the extent that planets are necessary for the origin and evolution of life, these exciting discoveries certainly augur well for the widely held view that life pervades the universe. This view is supported by advances in our understanding of the history of life on Earth, which have highlighted the speed with which life became established on this planet. The oldest direct evidence we have for life on Earth consists of fossilized bacteria in 3. 5-billion-year-old rocks from Western Australia, announced in 1993 by J. William Schopf of the University of California at Los Angeles. These organisms were already quite advanced and must themselves have had a long evolutionary history. Thus, the actual origin of life, assuming it to be indigenous to Earth, must have occurred closer to four billion years ago.