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A Journey to a New Land

Caribou Hunt
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Dr. Michael Wilson

Geology Department, Douglas College

Radiocarbon Dating

In the upper atmosphere, we have the conversion of 14nitrogen, stable nitrogen, into 14carbon which is an unstable isotope of carbon. That carbon circulates through the atmosphere, in carbon dioxide for the most part, and is taken in by organisms. Organisms at the earth’s surface, when they take in carbon, they are taking in the normal form of carbon, the stable form, which is 12carbon. They are also taking in 14carbon, and they are also taking in another isotope, 13carbon, which is relatively stable, too. So when we get a radiocarbon date, what we are trying to do is to convert the amount of 14carbon that we can measure in a sample into a date.

So what’s going on here? The 14carbon is unstable, it’s a radioactive isotope, and over time it decays back through beta emission, it changes back to 14nitrogen and it’s lost. To compute a radiocarbon date then, we have to compute the amount of 14carbon that is present and compare it to the amount of 12carbon and 13carbon that are present in the sample and the ratio that we determine gives us an idea of how long it has taken for this ancient sample to change from the state that it had when it was alive. We take in 14carbon of course during life; we are always taking in 14carbon, so we maintain a fairly constant level of it in our body. As soon as we die, the 14carbon starts to die, so the ratio between the 12carbon, 13carbon and 14carbon is going to change. That’s the basis for our date. So that’s an absolute dating technique.