 Quote by kirkmcloren
Not only must oxygen be in a range high enough to support life -- and that means pressure as well as percentage.
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Life on Earth started before the high-oxygen atmosphere we have today. The oxygen content in our atmosphere is a result (byproduct) of life.
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There must be adequate water and it must be liquid.
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It's true that a lot of the current exploration is focused on places with liquid water.
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We also see that chemical reactions are very thermally dependent thus fevers over 107 are lethal.
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107 is lethal for humans (and presumably closely related animals). Other species we know of find that downright chilly (thermophiles).
http://www.nps.gov/yell/nature/thermophiles/biopro.html
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and the necessary wavelengths and intensity must be there for photo based life (plants).
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Presumably, if the other conditions are right, then photosynthetic species may be able to adapt to a variety of solar outputs.
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I think the odds must be 1 in billions or trillions for a suitable environment.
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Life on Earth has managed to survive in a wide variety of conditions...high/low pressure, high/low temperature, aerobic/anaerobic, acidic/alkaline, high in the atmosphere/deep in the earth, lots/little water, lots/no sunlight, etc.
I think there are many chances for suitable environments, particularly for microbial-type life. The trick would be in whether life could get started. That process is not well understood.