Science Questions

Sat, 9th Sep 2006

Part of the show Hot Nectar, Warming Weather and Birds Missing the Spring

Question

Roland in Cambridgeshire asked:

Can you tell me how carbon dating works?

Answer

With carbon dating we're talking about different isotopes of carbon. This basically means different forms of the element. Most of the carbon in the world is a form called carbon 12, which means that there are six neutrons and six protons in the nucleus. There is also a heavier but much rarer form of carbon called carbon 14 and that's also slightly radioactive. The fact that it is radioactive means that it will break down over time. When plants photosynthesise, they take on some of this C14 and have an amount of it in their tissues. Once they die, that carbon 14 starts to break down. If you can measure the amount of carbon 14 in that organism, you can tell how long ago it died. It's effective for about 40 000 years.

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