Carbon-14 Dating

I’ve taken a bit of a break for the last few years. In that time, I’ve finished my PhD in molecular biology and I’ve started a post-doctoral fellowship. I’m very glad to be back with Persephone  and to be answering your science questions!

Today, I’m going to talk about carbon-14 dating. Prior to researching this process, I had not really considered it beyond the general knowledge that archaeologists use it to date items. I hope to shed some light on the process. If you have remaining question, please ask and I will endeavor to answer them!

Radiocarbon dating, also known as carbon-14 dating, was invented by an American physicist named Willard Libby. Libby worked for a period of time developing Geiger counters sensitive to detect weak levels of radioactivity. Radioactivity comes in different flavors: alpha, beta, and gamma particles. These flavors have specific qualities and uses in medicine, research, and weapons. Those differences aren’t particularly important for this discussion, but I highly suggest that you take a look around if you’re interested. Especially regarding gamma particles since they were used to make the Hulk and are emitted by the Tesseract.

Libby spent time during World War II working on the Manhattan Project with scientists such as J. Robert Oppenheimer, Richard P. Feynman and many others.  In 1949, Libby developed (with help from his post-doctoral fellow and graduate student)  carbon-14. Additionally, he developed a method by which water can be dated using tritium, also known as H-3, meaning that wine can be dated (yay old wine).  In 1960, he was awarded the Nobel Prize in Chemistry for this work.

Willard Libby
Willard Libby via Wikipedia

As for radiocarbon dating, the concept is generally simple. Carbon usually exists as carbon-12, meaning that there are 6 protons, 6 neutrons, and 6 electrons, with a small amount (1%) of total carbon being carbon-13 and trace amounts existing of the carbon of our interest, carbon-14. Carbon-14 is generated when cosmic rays strike nitrogen-14 in the atmosphere, creating carbon-14 and a hydrogen (see figure).  These carbon-14 atoms collide with oxygen to produce carbon dioxide. Plants, as you know, take in carbon dioxide and this carbon-14 is incorporated into plants. Animals ingest the plant-based carbon-14 and humans ingest the plant and animal based carbon-14. Upon death of the plant, animal, or human, carbon-14 is no longer incorporated into the body and the carbon-14 begins to decay, returning to nitrogen-14 by a process called beta decay.

Flowchart of radiocarbon deterioration

It takes 5,700 years for half the radioactivity of carbon-14 to decay; this is what is referred to as the “half-life” of the molecule. All radioactive particles have a half-life, examples of which include 32P, used in research has a half-life of 14 days, and uranium 236, which has a half-life of 2.386×107 or 23,680,000 years. Libby and his lab calculated the amount of carbon-14 in the atmosphere over the past approximately 50,000 years which allows scientists, archaeologists, and anthropologists to use specialized radiation detectors to then calculate where on the chart the object of study falls with regard to age.

A few interesting things about carbon-dating:  testing of nuclear bombs from 1955-1970 deposited a massive amount of carbon-14 into the atmosphere. Knowledge of this fact has allowed scientists to calculate the number of cells regenerating in the heart. This is interesting because scientists had previously believed the heart was a terminally differentiated organ; the main cell type in the heart (cardiomyocyte) was thought not to regenerate or divide after a brief pre-natal period.

This knowledge has led to clinical trials in which cells are injected into the heart after a cardiac event such as a myocardial infarction (heart attack). The early data seem to indicate that there is a benefit from being treated with these cells. Of course, this is a topic hotly under debate in the cardiovascular research field, with many more experiments required to elucidate the basic science.

I hope I’ve given you some insight into the process of carbon-14 dating and the importance of the process in life, science, and medicine! Feel free to ask anything you like.



5 replies on “Carbon-14 Dating”

Could you perhaps one day explain how Avogadro got his number? While I quite enjoy my mental image of some Renaissance era dude hunched over a microscope with a veeerrrryyy tiny pair of tweezers, I’m betting it’s more complicated than that!

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