Question

What do you consider to be the basic requirements to classify something as a lifeform?

The definition of life, as you have probably guessed, is not something easily agreed upon in the scientific community. However, in order to understand the origins of life here on Earth as well as its possibilities elsewhere in the universe, scientists must set limits on the accepted definitions of living systems. In general, astrobiologists agree that life is a property of matter, and it may be investigated like any other property of matter, such as magnetism. We tend to consider the most distinguishing characteristics of living matter to be the abilities to reproduce and evolve. In fact, Bruce Jakosky's book, The Search for Life on Other Planets, defines being “alive” in general terms if the object 1) utilizes energy from some source to drive chemical reactions, 2) is capable of reproduction, and 3) can undergo evolution. This definition is subject to several complications, however. For example, fire can reproduce itself, contains heat energy, and uses biogenic elements (carbon, hydrogen, oxygen, nitrogen, phosphorous, and sulfur). And yet, fire it is classified as a byproduct of non-biological chemical reactions than of life, in part because it cannot evolve. For more information on the complications of defining life, see http://cass.jsc.nasa.gov/publications/MSR/DesMarai/DesABST.html
October 29, 2001