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Carbon dating
Intermediate
Age estimated from C-14 decay.
decayLiving things take in carbon-14 (T½ 5730 years) at a steady ratio; after death it decays. Measuring the remaining fraction gives age: t = (T½/ln 2)ln(N₀/N).
25% remaining: 11,460 years.
Valid up to about 50,000 years.
In more detail
Radiocarbon dating uses the decay of carbon-14 in once-living material to estimate its age. Living organisms maintain a constant ratio of carbon-14 to carbon-12, which stops after death.
Real-world uses
- Archaeologists date wood, bone and textiles using radiocarbon.
- Geologists use other isotopes for older rocks.
- Archaeologists date wood, bone and cloth up to about 50,000 years old using the remaining carbon-14.
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Frequently asked questions
How old can samples be?
Typically up to about 50,000 years, after which too little carbon-14 remains.
Why does the ratio change after death?
Because the organism no longer takes up new carbon, so carbon-14 decays away.
Why does carbon dating stop working after tens of thousands of years?
Too little carbon-14 remains to measure accurately, after about ten half-lives.
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