Tom Aust asked:
Hello - I really enjoy your podcast.
I don't know when you might be discussing something related to this but ... I was listening to a Johnny Cash tune the other day and he wanted to get away from this woman and "go where the air ain't been breathed before". Is that possible (that the air hasn't been breathed before)? Especially in light of the thousands of species that have preceded us. Thanks.
Dave - It rather depends what you mean by not being breathed before. If you're only interested in the molecules not having been breathed in before - and specifically if you're interested in the oxygen and nothing else - then any oxygen molecule you're breathing in either hasn’t been breathed before at all - or it can’t have been breathed more that a few times, because otherwise it wouldn’t be oxygen anymore it would be carbon dioxide!
But, if you're thinking about the actual atoms and whether any of the atoms have ever been breathed before, that's a whole different kettle of fish.
But then again, I wouldn’t say for definite that all of the atoms, all the molecules that you breath in have been breathed before, because there are 6 with 23 zeros (6 x 1023), or maybe as low as maybe 3 with 23 zeros (3 x 1023), molecules of gas in every lung full of air, and some of those might well have just been sitting there since the beginning of the Earth.
Also, some atoms have been coming out of volcanoes or degassing out of the centre of the Earth, and some have been raining in from space. So, in a normal breath, a few atoms won't have been breathed before, but I think most of the air will, wherever you are.
I should think just about every atom of our atmosphere has done the rounds many times over. Don_1, Thu, 3rd Nov 2011
Not quite all of them. There are some that certainly have not. Bored chemist, Thu, 3rd Nov 2011
I saw a piece of air today and it looked brand newe ! neilep, Thu, 3rd Nov 2011
Some bits, yes. Most (all?) of the oxygen in the atmosphere was produced because living things exhaled it. Geezer, Fri, 4th Nov 2011
Some of the gases in the air we breathe have come from decay of heavy radioactive elements in rocks ...