Why is there air?

Answer 1

Depends in which sense you mean the question.

"Why should we happen to live on a planet with air?" - because oxygen is a pretty reactive gas, so interesting chemical reactions (e.g. life) can happen. The 78% nitrogen is so that the oxygen doesn't destroy things just a bit too quickly. Gases are handy for this sort of thing because they get everywhere; sulphur, which of course is in the same group as oxygen and therefore has similar chemical properties, would be useless as a main engine of life because the only places anything could live would be at sulphur deposits. Of course if we had a really hot planet where there were large amounts of gaseous sulphur around, the life forms there (if any could exist, which is probably unlikely) might well use sulphur as their main oxidant (and would doubtless think of oxygen as a powerful sulphidant!) An atmosphere with moderate amounts of gaseous chlorine is also plausible for life, for the same reasons that an oxygen one is.

If you want to know the actual physical processes by which Earth acquired its present atmosphere, I can't help you a great deal; but the gist is that the general opinion seems to be that we started off with a odd mix as the Earth condensed, the lighter gases boiled away, some more rather unpleasant bits were added through vulcanism etc., then photosynthetic plants appeared and gave us some oxygen. This allowed some of the nastier stuff to get combined and/or locked away, leaving us with the air we have now. Plus the extra CO2 and CFCs and so forth that we've been dumping into it lately, of course.

Answer 2

If by "air" you mean oxygen:

Oxygen is the third most abundant element in the universe and makes up nearly 21% of the earth's atmosphere. Oxygen accounts for nearly half of the mass of the earth's crust, two thirds of the mass of the human body and nine tenths of the mass of water. Large amounts of oxygen can be extracted from liquefied air through a process known as fractional distillation. Oxygen can also be produced through the electrolysis of water or by heating potassium chlorate (KClO3).

Oxygen is essential for life and it takes part in processes of combustion, its biological functions in respiration make it important.
Oxygen is sparingly soluble in water, but the small quantity of dissolved oxygen in is essential to the life of fish.

However, "air" can be made up of oxygen and just about any other gas. It all depends on where you are in the world. Is the air "fresh" or heavily polluted? So, it really depends.

Answer 3

Any Phys. Ed. major know the answer to that. To fill up basketballs, footballs and volleyballs.

Answer 4

Inside car tires!

Answer 5

So we can Breath