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.
So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.
On the window sill of Prior's office sits the Californian personalised number plate CARBN14, which she used before moving to New Zealand in 1997.
It's that radioactive form of carbon – known as C14 – that is the key to discovering whether a carved ivory sculpture is an antiquity or a modern sham feeding poachers' coffers; whether a water bore is sucking dry an age-old aquifer or tapping a renewable store; whether a picture frame predates the painting in it.
It is produced in the upper atmosphere by radiation from the sun.
(Specifically, neutrons hit nitrogen-14 atoms and transmute them to carbon.) Land plants, such as trees, get their carbon from carbon dioxide in the air. The same is true of any creature that gets its carbon by eating such plants. Suppose such a creature dies, and the body is preserved.
It is also standard to coat fossils during their extraction and transport.
Acetone is sometimes used while extracting fossils, because it dissolves dirt.
Lab manager Dr Christine Prior already has bad news for another client – an art authenticator in Hong Kong.