Radiocarbon dating, right? How does that work, and how can we ensure its accuracy?
In: Planetary Science
When an organism is alive, it’s constantly got carbon moving in and out of its body. Plants take in CO2 from the environment and photosynthesize it, animals eat plants, and cellular respiration turns that food back into CO2 that releases into the air. So the carbon in the bodies of living things and the carbon that’s outside our bodies are all interchanging.
When an organism dies, it stops exchanging carbon with the environment. There’s a particular form of carbon, C-14, that is radioactive – it decays over time into the more stable form of C-12. And because those C-14 atoms are just randomly dispersed around, everything living has about the same proportion of C-14 – just a tiny percentage of their total carbon. Which means that anything that’s been dead for a significant amount of time is going to have less C-14 than average, and more C-12 than average, because some of that C-14 will have decayed and not been replaced.
We know that the half-life of C-14 (the time it takes for half of the amount in a sample to decay) is around 5,700 years. So if a dead plant has half the amount of C-14 we’d expect, then it’s been dead around 5,700 years. If it has a quarter the amount, it’s been dead around 11,400 years. And so on. Once you get past around 50,000 years, there’s not enough C-14 left to measure it well, so that’s the cap for archaeologists to study. But other radioactive materials can be used in some cases to date older materials, through a similar idea.
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