Biosignature

A biosignature is observable chemical, morphological or other evidence attributable to biological activity after assessing plausible abiotic explanations. It can concern present or past life on Earth or elsewhere. An exoplanet biosignature is the remote planetary specialization, requiring atmospheric and environmental context.

Retention of potential biological evidence through deposition, burial, alteration and exposure. Organic molecules, microscopic textures and isotope fractionation have different sensitivities to heating, oxidation and ionizing radiation. A former habitable environment can lack a recoverable biosignature if its record was destroyed; a preserved feature still requires tests against nonbiological origins and contamination.