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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.

This is the remote planetary specialization of a biosignature.

An exoplanet biosignature is an observable gas, surface feature, temporal variation, or chemical disequilibrium whose biological explanation survives plausible abiotic alternatives and environmental context.