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A more accurate sign of life on a planet is the presence of ozone in the planet’s atmosphere. This is created from oxygen by the radiation from a local star, which means that the exoplanet maintains a certain temperature. Oxygen is a by-product of the processing of CO2 by a whole range of different living things on planet Earth, and we can assume that something similar happens on exoplanets. So, if there is a combination of low carbon dioxide combined with high ozone, there is likely to be a significant biomass living near water. Which is the starting conditions for life.