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A comment on A sealed bottle garden thriving after 40 years without fresh air or water. Parent comment

Re:A sealed bottle garden thriving after 40 years without fr... by mikeash on Friday June 06, 2014 @11:33AM (#7858493)
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.

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Re:A sealed bottle garden thriving after 40 years without fr... by Coincoin on Friday June 06, 2014 @04:30PM (#7860129)
We could also use tritium for dating the water.
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Re:A sealed bottle garden thriving after 40 years without fr... by saalweachter on Friday June 06, 2014 @09:25PM (#7860950)
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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