After getting the planet above an 80% life likelihood, life should start appearing, according to the light spectrum of a star. An example is that the atmosphere reflects different spectrums of light through, or the stars spectrum is different from G2, our Suns spectrum. For example, Life should be black if the star is high in infra red radiation, like a red dwarf. More info here: :http://www.nasa.gov/centers/goddard/news/topstory/2007/spectrum_plants.html
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