Comment on Half-million-year-old wooden structure unearthed in Zambia

• northendtrooper@lemmy.ca ⁨1⁩ ⁨year⁩ ago

  Interesting, I didn’t think of the tree rings for fine tuning.

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  • fossilesque@mander.xyz ⁨1⁩ ⁨year⁩ ago

    www.youtube.com/watch?v=xcib9Fnv7-Y

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• TauZero@mander.xyz ⁨1⁩ ⁨year⁩ ago

  How could carbon-14 possibly work for anything half a million years old? That’s 87 half-lives!

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  • fossilesque@mander.xyz ⁨1⁩ ⁨year⁩ ago

    Ha, you’re right. Totally forgot there’s that upper limit (To be fair I don’t really do anything with stuff that old and I’m having waiting for dinner scatterbrains. :) ) . Going to have to dive into the paper I guess!

    www.nature.com/articles/s41586-023-06557-9

    Looks like they did luminescence. More about that here: projects.arch.ox.ac.uk/luminescence.html

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    • TauZero@mander.xyz ⁨1⁩ ⁨year⁩ ago

      Aha! The supplemental materials contain all the interesting stuff, like some cool photos of the excavation site:

      Image

      And section 2 goes into details about how the soil samples were collected and prepared for luminescence measurement, including keeping them in the dark/under red light lab room conditions while they were washed in acid for 3 days, before shining a laser on them. They even stuck gamma radiation probes into the holes they dug the samples from to measure the current background radiation levels there.

      Interestingly in their calculation, only 5% of radiation comes from cosmic rays, and 95% from decay of nearby radioisotopes of uranium, thorium, and potassium. They were worried whether cyclical sedimentation/erosion activity of the adjacent river would change the thickness of the soil overlying the archeological site, thus affecting amount of cosmic radiation reaching it. Turns out for the final age calculation it didn’t make much of a difference whether the soil was usually 5 meters thick or 10.

      I would still need to read the reference papers to figure out how accumulated radiation is related to luminescence under a laser in the first place.

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• Shdwdrgn@mander.xyz ⁨1⁩ ⁨year⁩ ago

  Ohhh is this the technique where they line up the tree rings with known climate events? It’s certainly cool how many different methods they come up with to date things, although judging by the small size of those logs it doesn’t seem like they would have very many years to work with.

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  • fossilesque@mander.xyz ⁨1⁩ ⁨year⁩ ago

    Rangefinding helps narrow the window.

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