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Comment by hellbreakslose | Hacker News Reader

Hmm can we open the bottle and test if the water is indeed from 1972?

I mean how can we actually test that this guy isn't just making things up, and wasn't opening the bottle to water the ecosystem?

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Water recycles itself naturally. I'd be more curious to know how the oxygen converts back to carbon dioxide.

well I agree but I just can't believe anything like that nowadays... If you want people to believe that the bottle is sealed since 1972 then prove it as well. Not just a photo of a giant bottle with some plants in it.

Respiration. Microorganisms use oxygen, and so does the plant when it's not under sunlight.

Wait another 40 years.

I wonder if carbon dating would work. Seems like it ought to, since C14 is produced in the upper atmosphere, so if's been sealed then it wouldn't get any new C14. The small amount of decay over 42 years might be trouble to measure.

A potentially crazier idea: measure the trace amounts of uranium, plutonium, and other long-lived fallout products. Atmospheric nuclear testing continued on a semi-regular basis until 1980, and so the makeup and concentration of the fallout would be different if it had been unsealed after 1972.

We could also use tritium for dating the water.

Carbon-14 dating should work in principle, but in practice the error on carbon-14 dating is several decades. So that's out.

I'm not sure about tritium dating for the water. Reading the USGS website on it, it seems to indicate that the way tritium dating works is that they seal some water in a copper tube and see how much helium magically appears as the tritium decays. They ask for two 500mL (two 1 pint) samples.

So if tritium has been decaying into a sealed glass container for 40 years, should there be a measurable amount of helium in the container?

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