Carbon Dating - The Chemistry of Carbon-14

I was running around doing errands a couple of weeks ago and I decided to drop into the local Chick-fil-A for lunch. I waited my turn in line and then the young cashier called me up to her window. She said, “Welcome to Chick-fil-A.” Now I think I look young for my age but; and then she said, “Hi, what would you like in your order today?” But I definitely am in THAT age group. So then she took my order and when she handed me my receipt I saw it. She had given me the “Senior Discount!” I did not even need to ask! Now I was glad to get my 10% off but it made me think… Was it my graying at the temples, or my dewlap, or my crow’s feet that gave away my age?

The cashier used her deductive reasoning skills to assess my age and determined that I must be over 60, hence the Senior Discount. Scientists do the same thing when determining the age of plants or animals found in the fossil record. Particularly, they use carbon dating to determine the approximate age of organic materials that are considered to be less than 50,000 years old, the practical limit of this type of test.

All elements have what are called isotopes. An element is an atom with a set number of protons defining that specific element. For carbon that number is six protons. An isotope is each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Some isotopes are stable, such as carbon-12, and others, carbon-14 in particular, are radioactive forms of an element. Radioactive isotopes can release electromagnetic radiation or particle radiation to become stable. Particle radiation includes alpha and beta particles as well as proton and neutron radiation. Carbon-14 emits an electron and an electron antineutrino, converting one of the neutrons in the carbon-14 atom into a proton and thereby changing the carbon-14 into the stable isotope nitrogen-14.

Carbon-14′s half-life is about 5700 years, making it a good marker for items up to that 50,000 year limit we mentioned earlier. After about 50,000 years, almost all carbon-14 will be gone from a given fossil specimen once no more can be adsorbed. Once all the carbon-14 is gone, at about 50,000 years, the specimen can no longer be dated by this method.

Carbon is often considered as the foundation of life. Many molecules containing carbon, when bonded with hydrogen, oxygen and nitrogen, are considered organic and are part of the makeup of planets and animals. After water, carbon would be considered as an essential element in molecules discovered in the search for extraterrestrial life. I wrote about carbon in a previous blog post, “Gods Favorite Elements“.

So how does carbon dating work? The interaction of cosmic rays with atmospheric nitrogen is constantly creating carbon-14. This carbon then combines with atmospheric oxygen to form radioactive carbon dioxide (CO₂). The resulting carbon-14 carrying CO₂ is incorporated into plant molecules by photosynthesis and animals then acquire it by eating the plants. The amount of carbon-14 in the animal or plant continues to remain steady with the environment, until that plant or animal dies. Accumulation of the carbon-14 into the organism then stops and the amount of carbon-14 it contains begins to decrease as the carbon-14 undergoes radioactive decay. Measuring the amount of carbon-14 in a sample from a plant or animal fossil provides information that can be used to calculate when the organism died. The older a sample is, the less carbon-14 there is to be detected.

But it is not as simple as comparing the amount of carbon-14 in the fossil to a chart and getting its age. Presuming the rate of production of carbon-14 to be constant, the activity of a sample can be directly compared to the equilibrium activity of current living matter and the age calculated. But is the production of carbon-14 constant? Years of work were required to develop the technique to the point where accurate dates could be obtained. Research has been ongoing since the 1960s to determine what the proportion of carbon-14 in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of carbon-14 in a sample into an estimate of the sample’s calendar age.

But this calibration curve is also impacted by other factors – different types of organisms can have varying levels of carbon-14, burning of fossil fuels in the past 100 years has decreased the amount of carbon-14 in the atmosphere and nuclear tests in the past 50 years have added to it. So carbon dating may not work so well in the future. Carbon dating can be validated by other methods so the curve is constantly being refined. The use of various radioisotopes (along with carbon-14) allows the dating of biological and geological samples with a high degree of accuracy. But anything that died after the 1900s, when fossil fuels and open-air nuclear tests started changing carbon-14 concentrations, will be harder to precisely date.

Another possible problem with this dating method is the existence of carbon-14 in geological samples that are said to be millions of years old. In 1997 one group of scientists started a study of coal and diamond samples, previously tested by other means to be in the millions of years old, and therefore should contain no carbon-14. All of their samples, according to their tests, contained detectable levels of carbon-14 and thus would rate much younger by this method. They claim this shows proof of a young earth. Could this prove that earth is only about 10,000 years old?

The study of the age of fossils and geological materials does require some assumptions that makes their accuracy questionable but in the past 50+ years of development, scientists now have a remarkable understanding of most if not all of carbon dating’s subtleties and complexities. Carbon dating is a powerful tool in helping us understand the history of our world and all of God’s creation on it. Carbon dating provides another source of evidence that the Bible accurately describes the record of mankind.

Job 36:26 (NIV) – How great is God—beyond our understanding! The number of his years is past finding out.