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Radiocarbon Dating as a Current Scientific Clock
By Jonathan Ring
The use of carbon-14, also known as radiocarbon, to date organic materials has been an important method in both archaeology and geology. The technique was pioneered over fifty years ago by the physical chemist Willard Libby, who won the 1960 Nobel Prize for his work on 14C. Since then, the technique has been widely used and continually improved. This paper will focus on how the radiocarbon dating method works, how it is used by scientists, and how creationists have interpreted the results.
Carbon-14 is a radioactive isotope formed in the upper atmosphere. It is constantly being produced by a system in which cosmic rays from the sun hit atoms, releasing neutrons. The neutrons may then be absorbed by 14N (nitrogen-14) atoms which lose a proton in the process, becoming 14C. Carbon-14 becomes a part of the mostly homogenous mixture of air in the atmosphere. It can combine with other atoms and molecules such as oxygen to create carbon dioxide, or CO2. Through the process of photosynthesis, plants absorb carbon dioxide which contains 14C along with the much more abundant 12C and 13C. Animals then eat the plants and incorporate 14C into their own bodies, and eventually it is passed through the food chain. Through this process, every living thing eventually absorbs 14C into its body in a measurable ratio to 12C and 13C. Carbon-14 makes up an extremely small portion of the carbon on earth. Carbon-12 is the most common isotope and makes up just under 99% of all carbon. Carbon-13 comprises around 1%, and 14C makes up only a small fraction of a percent. In fact, there is about a trillion times more 12C in the atmosphere than 14C.
When the plant or animal dies, carbon ceases to be absorbed into its tissue. Since 14C decays over time, and the absorption of all carbon has stopped, the initial condition for a clock is the living ratio of the carbon isotopes. After a certain amount of time, the ratio of 14C to 12C, compared to a modern sample of the same type, will give a date for the object in question. Carbon-14 decays into 14N through the process called Beta decay with a half-life of approximately 5,730 years. The beta decay process consists of the atom of 14C ejecting an electron, or beta particle, out of the nucleus, converting a neutron to a proton in the process. The resulting atom, or daughter product, is 14N which has the same atomic number, but contains one more proton than the parent product.
A half-life works the same way in any type of decay. In the case of 14C, every 5,730 years half of the original 14C decays into nitrogen. At 11,460 years (2 half-lives) there is 1/4 of the original 14C, at 17,190 years (3 half-lives) there is 1/8 of the original 14C, and so on. Eventually, there is too little 14C left in a sample to accurately measure without contamination. Theoretically, radiocarbon techniques have the ability to date samples to around 75,000 years, but the working threshold of reliable dating is around 50,000 years. Samples significantly older than this have very little or even no measurable 14C left.
In order to function properly, natural clocks need an irreversible process that occurs at a constant and known rate. Nuclear decay has a constant rate of decay, but as it turns out, the formation of 14C in the atmosphere is not always constant. However, cross-checking techniques such as tree ring dating and coral analysis, 14C has been reliably calibrated to tens of thousands of years. The newest limit using cross-checking methods is around 26,000 years (Dotinga 2005). Without this calibration, atmospheric fluctuations in 14C cause some radiocarbon dates to have an error up to 10%.
Carbon isotopes are generally measured through the use of a machine called the accelerated mass spectrometer. A small portion of the sample is put into the machine which then vaporizes it. Taking advantage of the distinct mass of individual isotopes, the machine distinguishes the 14C from all of the other atoms and molecules present and is able to count the individual atoms. Charcoal, cloth, bone, or any other material that contains organic carbon can be dated using an accelerated mass spectrometer.
In conjunction with other creationist organizations, the Institute for Creation Research has assembled a team of researchers to challenge existing notions about the age of the Earth. The RATE team (Radioisotopes and the Age of the Earth) have studied a variety of subjects pertaining to the age of the Earth including radiocarbon dating. In the traditional model of science, radiocarbon has little to do with the age of the Earth, since its lifespan is so short. However, RATE is attempting to fit all radiometric dating into a young earth model. RATE researcher John Baumgardner has dealt specifically with radiocarbon dating.
The RATE research in the area of radiocarbon has focused on the "blank" sample date. According to the science behind radiocarbon dating, very old samples should have no measurable 14C left. However, conventional scientific research projects, as well as RATE research on coal beds and diamonds, have found samples which should no longer have any 14C but actually contain very small amounts of it. Since the accelerated mass spectrometer can detect 14C to a higher precision than what was found in the samples, the 14C is thought to exist because of some sort of unexplained phenomenon or contamination. Therefore, the RATE team has identified a valid anomaly in radiocarbon research which deserves further research.
Before proposing their alternate theory about the residual 14C found in very old samples, the Rate team first discusses the possibility of contamination. Besides the cosmic rays creating 14C in the atmosphere, other ways to create 14C have been identified. Alpha particle emissions from uranium and thorium decay can convert 14N into 14C just as it is formed in the atmosphere. 13C also has the possibility of converting to 14C by interacting with a thermal neutron. However, as Baumgardner discusses the possible contamination through these processes, he concludes that "production of 14C by thermal neutrons at presently observed levels in unable, by several orders of magnitude, to account for the 14C levels we measure" (Baumgardner 2005: 616).
The RATE team has used this anomaly to advance an alternative theory. Noting that 14C exists in samples which should be 14C dead and thus providing an age for the samples around 50,000 years, the RATE team has come up with a theory for how such an inconsistency could occur. After rejecting contamination as a possibility for the presence of background radiocarbon, the team has come up with a model in which the accounts outlined in the Bible, specifically Noah's flood, explains the observed 14C.
All of the individuals who participated in the research began with the same view on the age of the earth: it is very young. This view is spelled out in the summary book of the RATE project by DeYoung: "Each member of the RATE team holds to a high view of scripture. This means that we regard the bible as a uniquely inspired book given to mankind from the Creator" DeYoung 2005: 158). In creating their 14C model, that premise is used as the foundation. The logic for the theory is as follows: 1) The Bible reveals the age of the earth to be somewhere around 6,000 years. 2) Since the earth is only 6,000 years old, the entire group of life forms represented in the fossil record (save the most recent fossils) existed at the same time and were all buried together in the world-wide biblical flood. 3) Because all life existed at the same time, more organic carbon was present before the flood than after. 4) Since there was more carbon overall, but not more 14C (the cosmic rays likely produced carbon at the same rate in the beginning as it does now) the ratio of 14C to carbon-12 was much smaller than it is today. 5) Therefore, the oldest dates possible by radiocarbon dating of approximately 50,000 years are inflated by a scale of 10 because the use of modern ratios of 14C to 12C does not reflect the historical reality of ratios in the pre-flood world. This means that radiocarbon dating actually proves the fossils are 5,000 years old, not 50,000.
The RATE team has applied an inverse system of logic to the standard. They begin with the same assumption that they are trying to prove. Broken down, the logic holds that the Bible says that the earth is very young; therefore the earth is very young. Without such a beginning claim, the logic would be extremely bizarre. Basically, the claim made by the RATE team is that the maximum date of 50,000 years given by radiocarbon dating actually equals 6,000 years. However, the entire idea is based on an arbitrary, unproven assumption.
Without the Bible, there is no reason to believe that all of the life represented in the fossil record was alive at the same time, creating a different ratio of 14C to carbon-12 than we see now. There is also no reason, other than the Bible, to assume that there was a world-wide flood. The only plausible way to create a theory about how the background 14C found in old samples is evidence that the Earth is 6,000 years old is to begin with the Bible. This creates what is called circular, or cyclical, reasoning. Basically, the Bible proves that the Bible is correct, regardless of the science employed. However, the faulty logic of the RATE research project does not discount the fact that residual 14C exists in samples in which it should theoretically be absent.
Finally, Baumgardner's research concerning 14C is only a small part of the entire RATE research. The main focus of the research focuses on a newly formed theory of accelerated decay. However, the evidence of residual 14C does not actually fit within the larger outline of accelerated decay. According to Baumgardner, "A value of (the acceleration factor) ? large enough to produce to produce 500 million years worth of decay in 87Rb with a half-life of 48.4 billion years, for example, would entirely annihilate any 14C that might have been present before the accelerated decay episode occurred. Note that the half-life of 87Rb is 8.5 million times larger than the 14C half-life of 5730 years" (Baumgardner 2005: 620). To account for the discrepancy, Baumgardner offers the explanation that "whatever the physics was describing the decay acceleration, it did not operate in so simple a manner as to reduce temporarily the effective half-lives of all radioisotopes by the same factor" (Baumgardner 2005: 620).
The scientific community has yet to explain this anomaly, requiring the necessity for further study on the matter. However, radiocarbon dating should be looked at in a larger context. It is only used on a very small time-scale compared to the age of the earth. Other radiometric dating techniques are far more useful for discussing the age of the Earth.
- Baumgardner, John R. 2005. 14C evidence for a recent global flood and a young earth. Chapter 8 (pp. 587-630) in L. Vardiman, A.A. Snelling, and E.F. Chaffin (eds.) Radioisotopes and the Age of the Earth, Volume II: Results of a Young-Earth Creationist Research Initiative, Institute for Creation Research, El Cajon, California, 818 p.
- DeYoung, Don. 2005. Thousands. Not Billions: Challenging an Icon of Evolution, Questioning the Age of the Earth. Master Books, Forest Green Arkansas, 190 p.
- Dotinga, Randy. 2005. Carbon-Dating Clock Reset. Wired News. http://www.wired.com/news/print/0,1294,66753,00.html. Accessed on December 15, 2005
- Higham, Thomas. 1999. c14dating.com. Radiocarbon Laboratory, University of Waikato, New Zealand
- USGS. Radiometric Time Scale. http://pubs.usgs.gov/gip/geotime/radiometric.html. Last updated: June 13, 2001. Accessed on December 15, 2005