I was curious how life on Earth, or an Earth-like planet, would be effected by changes in the gases which make up our atmosphere.

Assuming there is a similar level of oxygen in an atmosphere, could other gases be reduced or even replaced and still be able to maintain life as we know it?

Not really biology, but if the following could be kept in mind too that would be amazing:

[To give some context, I would like to ask how a sky could be light blue with a purplish hue, which supports some life larger than what we see on Earth, but still capable of supporting life which we find on Earth.

I am assuming a slightly higher percentage of oxygen is needed, but what other gases which are none lethal, but give a purplish hue?]

Thank you to all who take the time to give an answer, very much appreciated!

  • $\begingroup$ This question would be much more on-topic on Worldbuilding. $\endgroup$
    – MattDMo
    Feb 25, 2016 at 0:00

1 Answer 1


The Earth is blue (at least the non-land mass) because of the light our atmosphere refracts from the sun. A planets color is primarily determined by distance from sun, not from gas components.

Most gas does not refract light. Therefore a planet's gaseous composition can not be identified based on color.

To elaborate on your primary question, gas composition balance is essential to most life on Earth. Carbon dioxide, for instance, is responsible for photosynthesis occurring in plants. Different concentrations will affects photosynthetic rates. Another example is that CO2 levels, CO levels, and hexa-fluoro-carbons affect the amount of heat trapped in this planet.

Gas composition is highly delicate and must stay in balance to preserve life on Earth.
Light refraction off planet


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