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Radiocarbon is an isotope with two extra neutrons, created by cosmic rays interacting with nitrogen in Earth's atmosphere.When a plant or animal is alive, it constantly replenishes trace amounts of radiocarbon in its tissues.But once it dies, no more fresh radiocarbon is absorbed, and what’s left starts to decay.
Samples from the past 70,000 years made of wood, charcoal, peat, bone, antler or one of many other carbonates may be dated using this technique.
“I think there is a strong compelling argument to re-date these key sites using single-grain OSL,” he says.
And sometimes the dating techniques are fine, but the stability of the sedimentary layers throws things into question.
This is now considered the more reliable technique.
The reason behind this is it’s nearly impossible to separate crystalline grains that were once exposed to sunlight, which continually “resets” any trapped charge, from those that had already been locked away in rocks and accumulating electrons for millennia.“Multi-grain analysis of rock shelter sediments has a tendency to give older than expected dates because it can incorporate grains from the bedrock which haven't been fully bleached by the sun,” says Spooner.
“Unlike bone or charcoal, carbon preserved in eggshell is very stably locked in and unlikely to have been contaminated,” says Nigel Spooner, a physicist at the University of Adelaide in Australia who specialises in dating techniques.