Issues with Radiocarbon Dating

As I was flying home this weekend, I was thinking of what I could write my final blog about and I came up across the concept of radiocarbon dating in the book I was reading, Guns, Germs, and Steel. (I also came across The Shroud of Turin when I was watching the Pink Panther 2, but I didn’t think I could write a meaningful blog about such a ridiculous movie). I know that Imran had talked about radiocarbon dating in a previous blog, but I just wanted to talk about some of the problems of radiocarbon dating that were mentioned in this book.

During photosynthesis, plants intake atmospheric carbon. The ratio of carbon-14 to carbon-12, two isotopes of carbon, in atmospheric carbon is approximately 1:1,000,000. However, once a plant dies, approximately half of the carbon-14 decays into carbon-12 every 5700 years. Therefore, the date of a specific plant is based on the ratio of carbon-14 to carbon-12.

Until the 1980’s, scientists had a problem dating small materials found in archeological sites because a substantial amount of carbon needed to be collected from the source in order to determine its age. However, this problem was solved with a technique called accelerator mass spectrometry. This technique only required a very small sample and thus was vital in many historical discoveries. One example is that concept of food production. It was originally thought to originate in the Americas in 7000 B.C., but in fact, it originated in 3500 B.C.

However, another scientific discovery was that the ratio of carbon-14 to carbon-12 in the atmosphere is not always constant. This ratio changes with time. Therefore, some radiocarbon dates needed to be ‘calibrated’ with a new ratio. This was done with the help of growth rings in long-lived trees. The trees had a known specific date (based on the very accurate growth rings), and then the carbon ratio was analyzed in these trees to determine what the true ratio of carbon-14 to carbon-12 was during that age. This discovery had a strong influence on some archeological sites which were incorrectly dated based on the old ratio. Even now, other sites are still being accessed and calibrated so that the true dates of the sites can be known.

Like others, I just wanted to end this blog with a word of thanks and gratitude toward my peers and professors. I have never had an experience like these past five weeks and I will never forget it. I truly hope to see each and every one of you in the near future. Until then, Arrivederci!