Then, we have wood for which we know the right answer.
So, carbon dating has been calibrated against the rings of California bristlecone pines, and Irish bog oaks, and the like.
How it works Certain chemical elements have more than one type of atom. Carbon-12 makes up 99% of an atom, carbon-13 makes up 1% and carbon-14 – makes up 1 part per million.
Different atoms of the same element are called isotopes. Carbon-14 is radioactive and it is this radioactivity which is used to measure age.
Ive had a number of questions recently about ‘Radio carbon dating at Stonehenge’ Here is a comprehensive anwser: Radio carbon dating determines the age of ancient objects by means of measuring the amount of carbon-14 there is left in an object.
A man called Willard F Libby pioneered it at the University of Chicago in the 50’s. This is now the most widely used method of age estimation in the field of archaeology.
As the name suggests, fossil fuel is old, and no longer contains C14.
Half of the available atoms will change in a given period of time, known as the half-life.
The C14 will undergo radioactive decay, and after 5730 years, half of it will be gone. So, if we find such a body, the amount of C14 in it will tell us how long ago it was alive. The method doesn't work on things which didn't get their carbon from the air.
This leaves out aquatic creatures, since their carbon might (for example) come from dissolved carbonate rock.
If you hear of a carbon dating up in the millions of years, you're hearing a confused report. Second, they rarely contain any of the original carbon.
We can't date oil paints, because their oil is "old" carbon from petroleum. And third, it is common to soak new-found fossils in a preservative, such as shellac.