I had heard one time that with every breath you take, you inhale some molecules that were exhaled by Julius Caesar with his last breath. That sounded remotely plausible, so I decided to check it out with some quick calculations. I figured that the factoid is true, as long as the nitrogen molecules in the air have mostly been stable over the last couple of thousand years, and not cycled through plants more frequently than that.
I was never sure about that last bit - would the nitrogen molecules in the air hang around for thousands of years without being broken up by some process?
ETA:
Another factoid I heard is that the biggest contributor to nitrogen in the soil is a result of lightning breaking the molecules up and the non-N2 nitrogen falling with the rain. Is that right?
True, the post I was responding to was talking about gaseous nitrogen though.
For what it’s worth, nitrogen is relatively unreactive because it has a triple bond (i.e. a bond involving three electron pairs), which means you need to put in more energy to break those bonds before you form new ones. Triple bonds are relatively uncommon, but some other molecules like acetylene, carbon monoxide and cyanides also involve them.
It may be from a movie, but it was a trope here a few years ago. But when I saw it, I had the same response - Hey! I know that! But from where? And I still don’t remember. Vague sense that it was one of the answers in a long thread that evoked lots of speculation but nothing substantive. And then it got silly, hence: “It doesn’t do anything…” Older Dopers - set the wayback machine to the correct thread, please.
In the present atmosphere, the partial pressure of O2 is about 3 psi. If we removed all of the nitrogen, the pressure of the remaining O2 would still be 3 psi. IOW, nitrogen in the atmosphere doesn’t protect us from sea-level oxygen toxicity.
Likewise with nitrogen narcosis: removing O2 from the atmosphere wouldn’t change the partial pressure of nitrogen from its current value, and so we wouldn’t be at any greater risk of sea-level narcosis.
The effects on SCUBA divers would be a little more complicated. At present, a diver breathing air at 100 feet below sea level experiences an absolute pressure of 58.8 psi, at which point the partial pressure of O2 in his lungs is 12 psi (and the PP of N2 is 46.8 psi). If all of the nitrogen were taken out of the atmosphere, the sea-level pressure of the pure-O2 atmosphere would be 3 psi, but our diver will still see the pressure increase by 14.7 psi for every 33 feet of depth - except now that he’s breathing pure O2, the O2 pressure in his lungs will increase much more rapidly with depth than it does with our normal atmosphere: at 100 feet, the O2 pressure in his lungs will be 47.1 psi, compared to the 12 psi he had with a normal atmosphere.
The Wikipedia page for oxygen toxicity mentions a 45-minute safe time limit for exposure to an O2PP of 19 psi; 47.1 psi appears to be way off the deep end, so to speak.
So we land lubbers wouldn’t notice any immediate difference if all of the nitrogen were eliminated from the atmosphere, but SCUBA divers wouldn’t be able to go nearly as deep without using special blends of breathing gas.
