Radiocarbon dating is a method used by scientists to estimate the age of ancient objects that were once living matter, such as bone, leather, wood, or paper.
All of these contain carbon, a proportion of which is carbon- 14, a radioactive isotope that is continuously being formed in the upper atmosphere. Since living organisms take up radioactive carbon along with other carbon atoms, the ratio between the two forms remains constant. However, when an organism dies, the carbon - 1 4 in its cells decays and is not replaced. Carbon- 14 has a known half-life of 5730 years, so by measuring the concentration of carbon- 14 in an object, scientists can determine its approximate age.
One of the most successful applications of radiocarbon dating has been to determine the age of the Stonehenge monument in England (Figure 6.23). Samples taken from the remains of wooden posts were found to have a concentration of carbon- 1 4 that was 45% of that found in living material. What is the estimated age of these posts?
Figure 6.23

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raphy/Shutt