In the presentation speech for the 1960 Nobel Prize in Chemistry, one scientist described the work by honoree Willard Libby with these words: “Seldom has a single discovery in chemistry had such an impact on the thinking of so many fields of human endeavour. Seldom has a single discovery generated such wide public interest.”1 Libby’s research demonstrated the usefulness of carbon-14 in dating samples thousands of years old. Though radiocarbon dating clearly enjoys “wide public interest,” it also generates much confusion and discord among Christians, which leads to an obvious question: is Libby’s celebrated work a reliable technique for dating ancient objects?
The short answer is a resounding YES and here’s why.
The concept behind radiocarbon dating is rather simple. While organisms live, they incorporate radioactive carbon-14 from the atmosphere. The same applies to marine organisms, although with some well-understood subtleties. After the organism dies, the carbon-14 decays in a predictable way. By measuring the ratio of carbon-14 to stable carbon-12, scientists can then determine when the organism in question died.
When Libby developed the radiocarbon dating technique, he validated the method by comparing measured carbon ratios (carbon-14/carbon-12) from artifacts of known age with predictions of the ratio expected by assuming the decay rate. Libby found good agreement for artifacts with ages ranging from 1,000 to 5,000 years old.2 As scientists continued to develop the technique, they found ages as old as 20,000 and 30,000 years. Because these “much older” dates conflict with a reading of the Bible that contends the Earth is only 6,000–10,000 years old, some Christian organizations argue that radiocarbon dating does not give reliable dates past 5,000 years ago (the date these same organizations give for the timing of Noah’s flood). These Christians’ reasons for viewing the dates as unreliable include an assumption of unchanging amounts of carbon-14 in the atmosphere, an assumption about unchanging decay rates for carbon-14, and questionable calibration techniques.
Ongoing work in the field of radiocarbon dating actually addresses all these objections via the process used to calibrate a radiocarbon age. The calibration relies on finding independent ways to date other objects that contain carbon-14. Two excellent examples include tree rings and lake varves. Because of variations in the rate of growth (usually caused by seasons), tree rings provide an excellent way to generate a “fully-anchored” chronology of growth that extends as far back as 12,000 years.3 Measuring the carbon ratio from these tree-ring chronologies allows scientists to directly account for any changes in atmospheric carbon-14 and even any supposed changes in decay rates (a large body of evidence indicates these are constant but some measurements claim the possibility of small changes). Coupling the tree-ring data with analysis of organic material buried in yearly sedimentary layers laid down in Lake Suigetsu in Japan extend this chronology and calibration back to 50,000 years.4 Even without calibration, the carbon-14 dates and the tree-ring and varve dates show a strong correlation, which means that any variations in atmospheric carbon-14 (or possible changes in the decay rate) must be truly small. Years of calibrations have yielded straightforward tools for measuring that would be noncontroversial in other fields.
One final point worthy of note is that many scientists work to ensure the integrity of this calibration process and that group includes Christians and non-Christians. A person might feel comfortable claiming that non-Christians would actively seek to produce results that conflict with the Bible, but making the same claim for the believers involved stretches credibility.
Thus, if you are a scientist, based on the extensive work calibrating radiocarbon dating, the process largely amounts to determining what kind of sample you have and measuring the carbon-14 to carbon-12 ratio. Then you look through the calibration table for that measurement and read off the proper age. Obviously the details are slightly more complicated but the concept is simple. If you trust your ability to read a tax table to compute your taxes, utilize an ear thermometer to take a temperature, or even use a ruler to measure a length, you should also trust dates found using radiocarbon dating.
- Westgren, “Award Ceremony Speech,” in Nobel Lectures: Chemistry 1942–1962 (Amsterdam: Elsevier, 1964). Available online at http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html.
- R. Arnold and W. F. Libby, “Age Determinations by Radiocarbon Content: Checks with Samples of Known Age,” Science 110 (December 1949): 678–80.
- Paula J. Reimer et al., “IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50,000 Years Cal BP,” Radiocarbon 55, no. 4 (2013): 1869–87.
- Christopher Bronk Ramsey et al., “A Complete Terrestrial Radiocarbon Record for 11.2 to 52.8 kyr B.P.,” Science 338 (October 2012): 370–74.