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    Question ID:   18565         Current Version: 1
Question: Why do we have such an air composition on Earth?
Category: Science > Earth Sciences
Keywords: make up, composition, air
Type: why
Rating:(0 ratings)    Views: 83    Discussions: 0   In Watch Lists: 1  

 
    Answer:

Air is a mixture of gases. It is mostly nitrogen gas (N2) and oxygen gas (O2). There are also many other gases in smaller  amounts.

Incidentally, the Earth has a very peculiar atmosphere for a planet of its size. Generic small planet can have a stable atmosphere of only the most common and unreactive medium-size molecules --- e.g. nitrogen, carbon dioxide, ammonia, and methane (which indeed comprise the atmospheres of nearly all the other small bodies in the solar system). Lighter gases (hydrogen, helium) which are more common, and which form the bulk of atmospheres on giant planets like Jupiter, can escape the weak gravity. Highly reactive gases like oxygen or fluorine combine with rocks and are quickly removed from an atmosphere. But on Earth the presence of liquid water (in which carbon dioxide and ammonia dissolve) and living organisms (hungry for nitrogen and carbon containing compounds) has removed nearly all the carbon dioxide, ammonia and methane from our atmosphere, and photosynthetic plants keep a huge surplus of oxygen in the air, replenishing it as quickly as it is removed by chemical combination with surface rocks or respiration by living organisms. The small amount of helium present in the Earth's atmosphere works its way out from underground, where it is produced by the radioactive decay of heavy elements (uranium in particular).

Source: Argonne National Laboratory

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