Key Concepts

• If, as many scientists believe, life can readily emerge under the right environmental conditions, it is possible that life arose on Earth more than once. Researchers are now seeking evidence of a second genesis by searching for exotic microbes that are biochemically different from all known organisms.
• Some of the best places to look for alternative life-forms are ecologically isolated niches such as ocean-bottom volcanic vents and the dry valleys of Antarctica.
• Alien microbes may also lurk right under our noses. Scientists can hunt for these organisms by looking for the markers of alternative biochemistry.

The origin of life is one of the great unsolved problems of science. Nobody knows how, where or when life originated. About all that is known for certain is that microbial life had established itself on Earth by about three and a half billion years ago. In the absence of hard evidence of what came before, there is plenty of scope for disagreement.

Thirty years ago the prevailing view among biologists was that life resulted from a chemical fluke so improbable it would be unlikely to have happened twice in the observable universe. That conservative position was exemplified by Nobel Prize–winning French biologist Jacques Monod, who wrote in 1970: “Man at last knows that he is alone in the unfeeling immensity of the universe, out of which he emerged only by chance.” In recent years, however, the mood has shifted dramatically. In 1995 renowned Belgian biochemist Christian de Duve called life “a cosmic imperative” and declared “it is almost bound to arise” on any Earth-like planet. De Duve’s statement reinforced the belief among astrobiologists that the universe is teeming with life. Dubbed biological determinism by Robert Shapiro of New York University, this theory is sometimes expressed by saying that “life is written into the laws of nature.”

   
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