Dating with carbon-14


in Bombs and rockets, Geek stuff, Science, The environment

Emily Horn in tunnel on Ottawa River Pathway

When cosmic rays strike the atmosphere, they produce a radioactive isotope of carbon called carbon-14. This carbon gets absorbed from the atmosphere by living things. Once they die, they stop absorbing it. Since it continues to undergo radioactive decay after death, the ratio of carbon-14 to ordinary carbon declines in a predictable way in dead organic matter. This is the basis for radiocarbon dating.

When the great powers started testing nuclear and thermonuclear bombs during the Cold War, they doubled the ratio of carbon-14 to carbon-12 in the atmosphere. One consequence is the need to avoid contamination when radiocarbon dating. Another odder consequence is that you can determine the age of any person born since the tests began by looking at how much carbon-14 is in various layers of their tooth enamel. You just need to know whether they lived in the northern or southern hemisphere.

Of course, there are usually easier ways to determine the age of a living or dead human. This is just a demonstration of the extent to which the nuclear age is literally imprinted upon all those who live within it.

{ 7 comments… read them below or add one }

Woodsy June 12, 2008 at 5:27 pm

Oh, I thought you were offering dating advice as a follow up to the Elgin Street Irregulars latest postings…

Milan June 12, 2008 at 5:51 pm


I may well do some such thing in the future.

I suppose the above could have some dating implications. If you have doubts about how old someone claims to be – and are able to get your hands on one of their teeth – some lab work will reveal the truth.

Sarah June 12, 2008 at 6:23 pm

Conventionally one judges how old horses and sheep are by inspecting the teeth. The technique is a little different, though.

Woodsy June 12, 2008 at 8:00 pm

Hmmm… I better warn Aggie about the tooth plucking…

Milan June 12, 2008 at 8:30 pm

I am not the sort to wrench out body parts just to suppress curiosity about age. Numerical age isn’t terribly important to me.

. June 30, 2008 at 11:35 am

*how much carbon-14 is in various layers of their tooth enamel.

Milan June 30, 2008 at 6:12 pm


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