Everyone knows that stuff like Co2 warms the atmosphere (shocking I know). But I recently heard that if there was none of the natural Co2 we already have, the average temperatures on earth would be around -15 degrees Celsius (could be wrong about that number). I would assume that this is not ideal for life, and if this is the case, is Earth really in the habitable zone, or is it just habitable because of the greenhouse gases in the atmosphere that make it warmer? Is the variablity of the amount of greenhouse gases accounted for when calculating how big the band of the zone of habitability?
Edit: Got my answer, thanks everybody!
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That zone of habitability (sometimes called the “Goldilocks Zone”) is actually tied to whether there can be liquid water on the surface of a planet that has enough atmospheric pressure.
That condition is tied to the distance from the sun and how much energy it emits, and only accounts for the possibility that if there’s enough of an atmosphere, there would be the possibility of liquid water on the surface.
As to the temperature ranges that support life, plenty of life exists at temperatures of -15 degrees. The question of whether life as we understand it could evolve in such conditions is different, but many of the oldest forms of life are “extremeophiles”, existing in conditions we would normally not associate with being able to support life.
And lastly, carbon is extremely common- it would be unlikely to find any planet with an atmosphere that doesn’t have at least some CO2, or systems that emit CO2, like volcanoes.
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