Radiocarbon dating for dummies

13-Jul-2019 11:09

The pair of blue curves show the radiocarbon measurements on the tree rings (plus and minus one standard deviation) and the red curve on the left indicates the radiocarbon concentration in the sample.

The grey histogram shows possible ages for the sample (the higher the histogram the more likely that age is).

It is calculated on the assumption that the atmospheric radiocarbon concentration has always been the same as it was in 1950 and that the half-life of radiocarbon is 5568 years.

For this purpose `present' refers to 1950 so you do not have to know the year in which the measurement was made.

If we have a tree that is 500 years old we can measure the radiocarbon in the 500 rings and see what radiocarbon concentration corresponds to each calendar year.

Using very old trees (such as the Bristlecone Pines in the western U. A.), it is possible to make measurements back to a few thousand years ago.

For older periods we are able to use other records of with idependent age control to tell us about how radiocarbon changed in the past.

The information from measurements on tree rings and other samples of known age (including speleothems, marine corals and samples from sedimentary records with independent dating) are all compiled into calibration curves by the Int Cal group.

In this case, we might say that we could be 95% sure that the sample comes from between 1375 cal BC and 1129 cal BC.However, radioisotope dating may not work so well in the future.Anything that dies after the 1940s, when Nuclear bombs, nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely.To extend this method further we must use the fact that tree ring widths vary from year to year with changing weather patterns.By using these widths, it is possible to compare the tree rings in a dead tree to those in a tree that is still growing in the same region.

In this case, we might say that we could be 95% sure that the sample comes from between 1375 cal BC and 1129 cal BC.

However, radioisotope dating may not work so well in the future.

Anything that dies after the 1940s, when Nuclear bombs, nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely.

To extend this method further we must use the fact that tree ring widths vary from year to year with changing weather patterns.

By using these widths, it is possible to compare the tree rings in a dead tree to those in a tree that is still growing in the same region.

See also ORAU's Explanation of Radiocarbon Results.