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Comment by vasco | Hacker News Reader

Is my understanding of carbon dating needing an update or the precision to distinguish 100y difference on a 1.2k to 1.3k years base not enough?

If 100y is the difference it could just be that the tree grew for 100y and the at the end they used it?

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That is not an issue, because the tree will have been absorbing freshly made atmospheric carbon-14 until it died, at which point it starts to decay into carbon-12. So carbon-14 dating pinpoints the time of death, if you get the methodology right. We apparently now use accelerator mass spectrometers to just outright count all the atoms of c-14 and c-12. But in the 70s c-14 dating was notoriously tricky and full of pitfalls to with calibration and contamination and estimation, and it looks like we've only reduced the last of those possible sources of errors, the need for estimation, and the rest of it is still sketchy.

So as long as the tree was felled or died close enough to being used it'd still be accurate. Thanks!

But C-14 decay doesn't start with the tree's death, or does it? I assume that a live tree will also contain a certain amount of C-12. What would the result be if we carbon-dated one of the roots of the giant sequoia's in California, versus one of its branch tips?

It's nearly all carbon-12, yes. So you're asking how long it takes a giant sequoia to pump carbon dioxide from its needles [leaves?] to its nethermost reaches. Something like 80 feet. I don't know, but if it takes a year, I'd be surprised and impressed. Further investigation of plant respiration might show that every cell has to exchange gas with the outside on a daily cycle, but I'm not sure.

Wood stored underwater is a thing. Lots of places use bog wood, drowned trees. Down deep, it just goes on being wood.

Tree ring databases are pretty good. I think they cross calibrate to radio carbon maybe.

In New Zealand 50,000 yr old ancient Kauri trees are literally mined in swampy ground.

Most likely they used trees that had grown for at least 100y, as that's how you get the hardest wood (wood from young trees gets all bent in humid weather)

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