Chemical expansion in search for ET

Geobiologists at the University of Southern California reckon that thenarrow search for water could miss important clues to extraterrestriallife. They suggest the search should be widened to look for signs oforganic nitrogen as a direct indicator of life, because nitrogen isessential to the chemistry of living organisms. "It's hard to imaginelife without water," says Kenneth Nealson, "but it's easy to imaginewater without life." On the other hand, the discovery of nitrogen onMars, for instance, would be a different story. "If you found nitrogenin abundance on Mars, you would get extremely excited because itshouldn't be there," Nealson adds. Unlike carbon, nitrogen is not amajor component of minerals, so the presence of any substantial organicnitrogen deposits in the Martian soil would have almost certainly haveresulted from biological activity.