Alternative Atmospheres for Life

[Yae Miteo]

Is it possible for life to exist on a planet with an atmosphere radically different from earth's? Where the organisms breathe gases other than oxygen or carbon dioxide?

 

[Borek]

Short answer: we don't know.

Long answer: we don't know, we can only speculate about. Speculation is not something we do at Physics Forums.

 

[Yae Miteo]

Right. Sorry!

 

[Ygggdrasil]

It's worth noting that the composition of gasses in Earth's atmosphere has not been constant throughout the history of life on Earth. Early Earth's atmosphere did not contain oxygen, and early organisms did not use aerobic respiration. Only after cyanobacteria evolved photosynthesis did the Earth's atmosphere begin to have significant amounts of oxygen and other organisms could evolve to use that oxygen for metabolic processes.

 

[Evo]

It's worth noting that the composition of gasses in Earth's atmosphere has not been constant throughout the history of life on Earth. Early Earth's atmosphere did not contain oxygen, and early organisms did not use aerobic respiration. Only after cyanobacteria evolved photosynthesis did the Earth's atmosphere begin to have significant amounts of oxygen and other organisms could evolve to use that oxygen for metabolic processes.

And stromatolites are the results.

While prokaryotic cyanobacteria reproduce asexually through cell division, they were instrumental in priming the environment for the evolutionary development of more complex eukaryotic organisms. Cyanobacteria (as well as extremophile Gammaproteobacteria) are thought to be largely responsible for increasing the amount of oxygen in the primeval Earth's atmosphere through their continuing photosynthesis. Cyanobacteria use water, carbon dioxide, and sunlight to create their food.

http://en.wikipedia.org/wiki/Stromatolite

 

[Annihilator]

The Earth's atmosphere even now isn't static. There are pockets around this planet where the atmospheric conditions conductive to some forms of life are lethal to others. So we don't have to leave our planet or go back in time. Extremophiles are very interesting. One thing to keep in mind is that experiments have been done to use a replacement chemical in synthetic experiment. Despite the controversy over certain ways some people did some poor science, ''Arsenic biochemistry'' is a good example of the synthetic possibilities.

 

[Cepacia]

It is more than possible, it is a major element of life on earth. As noted above, early life evolved in the absence of atmospheric oxygen at an effective level. Anaerobic organisms, for which oxygen is toxic, exist in innumerable environments.

 

[qraal]

Limits of Organic Life

The National Academy of Science produced this book about 6 years ago, which discusses the issues of alternative atmospheres: The Limits of Organic Life in Planetary Systems

Also there's this paper by Johnson Haas which discusses a biosphere based on halides as the active gases: The potential feasibility of chlorinic photosynthesis on exoplanets.

A much older discussion, though still pertinent, is John Campbell's discussion of life on Jupiter, from the 1930s: Other Eyes Watching. While our model of Jupiter has changed, there has been much discussion of biospheres on hydrogen rich planets in recent years - even Earth is suspected of quite high hydrogen partial pressures in the past.