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Atmospheric carbon-14 spike caused by nuclear testing.
Atmospheric carbon-14 spike caused by nuclear testing.

Natural Selections: Fallout and carbon dating

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Curt Stager and Martha Foley discuss radiocarbon dating. Fallout from atmospheric testing of nuclear weapons has distorted the background levels of the radioactive isotope carbon-14, used by archaeologists to date organic materials. But it has an upside, providing a new scale by which to date more recent events, helping researchers track cell turnover in different parts of the body and in testing the age of everything from vintage wine to elephant ivory.

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Nuclear pollution from bomb testing has thrown off background levels of carbon-14, a radioactive isotope that is used to date organic materials. Carbon-14 is primarily used by archaeologists who are examining very old items. Everything contains carbon-14, and it breaks down naturally from radioactive decay. As a result, examining the levels of carbon-14 in an object can allow archaeologists to determine the object’s age.

The bombs loaded carbon-14 into objects and rendered the old system obsolete. “Ironically, you can use it in other ways to date modern things,” said Dr. Curt Stager of Paul Smith’s College. Nuclear bomb pollution has been diminishing since the 1950s and is more strictly regulated. However, people born then, during the onset of the pollution, have parts that are radioactive.

“There always was some natural carbon-14 in the environment so everybody’s got that, but it pretty much doubled the natural amount in the atmosphere,” said Stager. “There’s a lot more in certain parts of our bodies, which is kind of creepy because there could potentially be health effects of that.”

On the bright side, Stager says that medical researchers have made use of the elevated levels of radioactive isotopes to find answers to outstanding questions about human bodies and cells. Stager said, “One question was, how long do your cells stick around?” Other questions included whether or not brain cells are replaced, and if fat cells disappear after an individual has lost weight.

“Those questions about are there are parts of our bodies that last a long time or all they all new, we find out because of that pollution,” said Stager. By checking the radioactivity of different body parts, researchers have determined that some parts are more radioactive than others. According to Stager, these parts were formed early on in life. These parts include teeth enamel, a part of the eyes inside the lens and memory cells in the brain. On the other hand, fat cells only last for about eight years and therefore have a relatively high turnover rate.

The radioactive isotopes released during the initial bomb tests allow scientists to date anything made during or after that time. Stager said, “People were worried about it during the nuclear tests, not only about nuclear war but about all of the effects. That’s why the ban went into effect. People have been monitoring how much pollution is there, starting in the ‘50s. So it’s a known amount as decreased year to year. So there’s a standard curve of carbon-14 concentrations.”

The amount of radioactive material in a body part or object can be measured and compared to this curve to determine how old it is. It is precise within approximately one year. It can be used to help identify victims in crime scenes and also to date items like vintage bottles of wine. Stager said that it can also be used with elephants, which are going extinct from over-hunting. An ivory ban prohibits currently hunting, and people who purchase items made of ivory can use carbon-14 dating to determine if the ivory was harvested prior to the ban.

Carbon-14 continues to diminish as time passes. “It’s not because the carbon’s breaking down, but it’s being buried in the soils and the bottom of the ocean,” said Stager.

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