I found it weirdly hard to Google an answer on this. Firstly, rates are given in terms of decays per second instead of in half-life which would be more relevant for our purposes. Secondly, it seems to be well studied in the interstellar medium than in atmospheric conditions.
Anyway, the most relevant measurements I could find [0] say photodisassociation of N2 in the interstellar medium happens at a rate of approximately 10^-10 s^-1 - i.e. every 10 billion seconds on average.
Caesar died about 60 billion seconds ago [1] so at that rate, many of the molecules would still be alive.
However, we don't live in the interstellar medium. By interstellar standards, we pretty much live on the surface of the sun. The average point in the ISM is maybe 2 light years from the nearest star [2] but we are only 10^-5 ly away. They're all the same photons, but radiation intensity diminishes with the square of the distance, so our nitrogen molecules should disassociate every 1 second instead. If that's true, Caesar's last breath had its last surviving molecules persist for only a minute or two after Caesar himself.
Maybe the ozone layer protects them? Your conclusion that nitrogen molecules in the atmosphere only survive a minute or so during the daytime isclearly wrong; if it were true, the atmosphere would be about 2% brown nitrogen dioxide like the output of a Birkeland–Eyde reactor a couple of minutes after the sun came up (or more, since the temperature and pressure are lower) and everyone would have died at sunrise today. Or, rather, biochemistry would look almost unimaginably different, having evolved to resist being oxidized by nitric acid.
UV breakdown doesn't appear as a significant source in http://nmsp.cals.cornell.edu/publications/factsheets/factshe... although lightning does. So, if this mechanism is operating at a significant scale in Earth's atmosphere, it's escaped the attention of the scientists who specialize in the terrestrial nitrogen cycle, which seems implausible.
Yeah, one minute didn't seem right, but I couldn't easily refute it. I figured maybe the free nitrogen atoms recombined with other ones milliseconds later, but as you point out the existence of Birkeland-Eyde process disproves that, a significant amount would react with the oxygen instead of each other.
The ozone layer blocks around 99% of UV light [0], the earth about 50%. That's two orders of magnitude accounted for, but even a dissociation rate of every few hours seems too fast.
True, but I think that only occurs in the upper atmosphere and at a very low rate. Atmospheric N2 is also converted by bacteria into ammonia, which is absorbed by plants. And lightning oxidizes N2, as do combustion engines. I'm not sure if all those different reactions add up to a significant fraction, though. It might be true that most of the N2 molecules from Caesar's time still exist.
> So I'm going to tell you about a trick you can pull right here at the point where the train tracks end. You can reinvent yourself. I wish I’d known I could do that. I was lazy in college and got bad grades
I googled study fees for that university. $69000 per year plus expenses for accommodation, food and books.
After you finish such school, you should be top level motivated professional with highly lucrative job lined up. If you drop quarter of million dollars for paper, just to discover at end you need to "reinvent yourself", you are probably highly highly privileged person, or just not so smart.
18 years old kids need to hear this speech. Not students before graduation!
The main "trick" here was moving to where the next center of power was going to be and meeting the right people through hard work (but really the main differentiator) sheer luck.
> If we assume that ... these molecules are preserved over time (a reasonable assumption—nitrogen is relatively inert),
But they are not inert. Single UV photon can break single N2 molecule bond.
Elemental N is highly reactive and will form new N2 molecule pretty fast, but that is NEW and different molecule!
N2 is not stable over period of 2000 years under constant exposure to solar UV radiation!