The Material-Independent Signatures of Life.Forensic Tools of Astrobiology

Abstract

Biological life is intimately related to the geochemical conditions on Earth and is fit for this planet’s energy flux. It has often been suggested that life was also built in accordance with the particular local conditions offered by the early Earth. Common sense dictates that the constructive details of life on another planet should also be a reflection of the particular local conditions. Moreover, the collective activity of all life forms on a planet should have some measurable consequences on the global geochemistry. Comparison with the Earth-bound type of life is certainly inspirational but only up to a point. One central rule in astrobiology is: life can be made of many things and can have many forms. The search for extraterrestrial life cannot be limited to the search for Earth-like examples. Despite the common sense of this guideline, a manifest tendency exists today to judge the geochemical conditions from other planets through Earth-colored glasses. Much too often we hear expressions such as conditions too hostile to harbor life’, or the search for Earth-like planets as potential hosts of life’, or chemistry appropriate for life’, or water as the fluid of life’, or terra-formation of another planet to make it appropriate for life’. Irrespectively of how hostile another planet might appear to our Earth-based metabolism, we cannot state with certainty that life cannot be present before a comprehensive investigation is performed which includes the search for life’s material-independent signatures.