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 the academic appointment above.
Australian National University provides funding as a member of The Conversation AU.
By comparing living trees with old lumber and finding overlapping ring patterns, scientists have established chronological records for some species that go back as far as 9,000 years.
The method was developed by Willard Libby in the late 1940s and soon became a standard tool for archaeologists.
The resulting radiocarbon combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died.
The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.
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.
Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.
Radiocarbon dates which have been corrected--or rather, calibrated--by comparison to dendrochronological records are designated by abbreviations such as cal BP, or calibrated years before the present.
See the cal BP discussion for additional information about radiocarbon calibration.
There are, however, physical reasons for expecting some changes in the 14C content of the atmosphere to have occurred and it is important...