An astrobiologist is describing the search for 'biosignatures' in exoplanet atmospheres. [1] Using spectroscopy, scientists analyze the light passing through a distant planet's atmosphere to identify specific gases. [2] The presence of oxygen and methane in high concentrations would be highly suggestive of life, as these gases tend to react and disappear unless they are constantly replenished. [3] However, scientists must be cautious, as geological processes like volcanism can also produce these gases in some environments.