Radiocarbon Dating
Carbon-14 decays so we can date organic remains.
About this topic
Radiocarbon dating estimates the age of organic materials up to about 50,000 years old by measuring carbon-14. Cosmic rays make carbon-14 in the upper atmosphere from nitrogen, and it is taken in by plants as carbon dioxide and passed to animals. While alive, an organism has the same ratio of C-14 to C-12 as the atmosphere; after death, no new C-14 is taken in and the existing C-14 decays by beta emission with a half-life of 5,730 years.
The age is found by comparing the remaining C-14 fraction with the living ratio. After one half-life, 50 percent is left; after two, 25 percent; after three, 12.5 percent. The formula is N = N0 x (1/2)^(t / 5730), so t = 5730 x log(N0/N) / log 2. Counting is done by measuring decay rate, or more precisely with accelerator mass spectrometry. Results are calibrated using tree rings and other records, since atmospheric C-14 levels have varied.
Worked example: a wooden tool has 25 percent of the C-14 of living wood. That is two half-lives, so it is about 11,460 years old. The method has dated the Dead Sea Scrolls, Otzi the Iceman and cave paintings. For rocks millions of years old, other isotopes like uranium-238 (half-life 4.5 billion years) are used.
Misconceptions: that it can date rocks or dinosaur fossils (it cannot; they are too old and not carbon-based in the right way), and that C-14 is rare because it is unstable. It is simply continuously made.
Key ideas
- Half-life 5730 years
- Living things take in C-14 constantly
- Works to about 50,000 years
Quick check
Use cases: where Radiocarbon Dating helps
- Homework: review the key idea behind Radiocarbon Dating before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Radiocarbon Dating without notes.
- Visual learning: play with the interactive lab to see how Radiocarbon Dating changes when you adjust its inputs.
- Teaching a friend: explain Radiocarbon Dating in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Radiocarbon Dating?
Carbon-14 decays so we can date organic remains.
What will I learn in Radiocarbon Dating?
Half-life 5730 years. Living things take in C-14 constantly. Works to about 50,000 years.
Is Radiocarbon Dating part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Radiocarbon Dating lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Radiocarbon Dating?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.