Why carbon dating works
The ratio of radiocarbon to stable carbon atoms in the atmosphere has varied in the past.
This is because the amount and strength of cosmic radiation entering the earth's atmosphere has varied over time.
When it comes to dating archaeological samples, several timescale problems arise.
For example, Christian time counts the birth of Christ as the beginning, AD 1 (Anno Domini); everything that occurred before Christ is counted backwards from AD as BC (Before Christ).
There are two techniques for dating in archaeological sites: relative and absolute dating.
Relative dating stems from the idea that something is younger or older relative to something else.
In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
The idea behind radiocarbon dating is straightforward, but years of work were required to develop the technique to the point where accurate dates could be obtained.(This, in turn, is caused by variations in the magnetic fields of the earth and sun, for example.) Although the ratio of radiocarbon to stable carbon in the atmosphere has varied over time, it is quite uniform around the globe at any given time because the atmosphere mixes very quickly and constantly.Plants obtain all their carbon atoms from the atmosphere.Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age.