Biosignatures of Past Life are Also Relevant to the Search for Extant Life

A biosignature (a “definitive biosignature” or DBS) is an object, substance pattern and/or process whose origin requires a biological agent. A potential biosignature (PBS) is a feature that might have a biological origin and thus compels investigators to gather more data before determining the presence or absence of life. The usefulness of a PBS is determined not only by the probability that life created it but also by the improbability that nonbiological processes produced it. Habitable planetary environments create nonbiological features that can mimic biosignatures, so these environments must be characterized to the extent necessary to confirm the presence of DBS. Environments also must have allowed biosignatures to be preserved and to remain amenable to detection.