Isotopes of a particular element have the same number of protons in their nucleus, but different numbers of neutrons.
This means that although they are very similar chemically, they have different masses.
If 1% of the carbon in a 50,000 year old sample is from a modern contaminant, the sample will be dated to around 40,000 years.
Because of this, radiocarbon chemists are continually developing new methods to more effectively clean materials.
Rachel Wood does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Australian National University provides funding as a member of The Conversation AU.
The calibrated date is also presented, either in BC or AD or with the unit cal BP (calibrated before present - before 1950).
Now the curve extends (tentatively) to 50,000 years.In addition, samples need to be thoroughly cleaned to remove carbon contamination from glues and soil before dating.This is particularly important for very old samples.In the 19th and early 20th century incredibly patient and careful archaeologists would link pottery and stone tools in different geographical areas by similarities in shape and patterning.Then, by using the idea that the styles of objects evolve, becoming increasing elaborate over time, they could place them in order relative to each other - a technique called seriation.