All organic material contains the isotope of carbon 14. After an organism dies, carbon 14 begins to decay at a predictable rate. Carbon 14 has an average half-life of 5,730 years. In other words, this is the amount of time that the remains of the organism will lose half its carbon 14 as they decay into nitrogen. Scientists can determine the age of a sample by measuring the ratio of carbon 14 to the more abundant and stable carbon 12 atoms.

Michener describes the process of radiocarbon dating on page 69 of The Source. Simply put, lab technicians count how quickly carbon 14 disintegrates in a sample. The older the sample, the slower the carbon 14 decays. This is compared to the levels of carbon 12 atoms that remain, giving a decent estimate of the sample's age.

This makes carbon 14 dating a very valuable tool that archaeologists use to determine the age of an artifact. Indeed, the archaeologists in The Source make use of it several times. When they find a good sample of preserved organic material, they send it to labs in Chicago and Stockholm for analysis. They use two labs so that the results can be cross-checked for greater accuracy. One artifact they do this with is a piece of charred ram's horn (p. 67). They find that this dates back to around 1400 BCE and helps determine a time when Makor was destroyed by fire.

They also use carbon dating to determine the period of Makor's earliest habitation. What exactly the sample they use is is not mentioned. However, they receive a telegram from the lab in Chicago that the sample from Level 19 is about 65,000 years old (p. 1067).