Bacterium Discovery Raises Questions About Definition of Life

December 2, 2010 -- NASA announced that researchers have discovered a bacterium in sediment at Lake Mono, Calif., that can use arsenic instead of phosphorus to grow, a significant discovery given that all other known forms of life rely on phosphorus, one of six essential elements required for existence. A 2007 National Research Council report found that the fundamental requirements for life as we generally know it are not the only ways to support phenomena recognized as life, and recommended that researchers keep that in mind when searching for evidence of life on other planets. The report also encouraged studies of extreme environments on Earth to look for organisms with novel biochemistries -- in other words, just the type of research that led to the discovery at Mono Lake.