Rights: The University of Waikato Published 17 September 2009 Download

Carbon-14 levels in the atmosphere vary over time, and this has implications for dating samples using the techniques employed by Dr Fiona Petchey. In this video, Fiona explains why calibration curves are used to convert the carbon-14 concentration age to a proper calendar age.

Points of interest
What are cosmic rays? What effect do they have on the Earth’s atmosphere?


What you get at the other end of the lab process is a number, so it will be 400 plus or minus 40 years. That is a C-14 concentration value, it is not a calendar age. So although it does approximate to about 400 years ago, it’s not exact.

There are a lot of assumptions in the original C-14 process. Some of those assumptions have been sorted out, and one of them was basically that C-14 was stable through time, and we now know that it isn’t, it fluctuates over time according to solar radiation and other things that have occurred in the atmosphere. What the whole radio carbon community have been developing over the last 20 or so years are calibration curves. And what they do is they get samples of known age, and they date them with radio carbon, and they’ve gone back over time getting progressively older samples of known age, and they can tie these in with the C-14 fluctuations in the atmosphere.

And those calibration curves are used to give a calendar age for a sample. So if we’ve got a moa bone, I’ll take that value and I’ll plug it into the calibration curve and it will spit out a calendar age for me or at least a calendar age range.