The history of radiocarbon dating
The main limitation of these techniques is sample size, as hundreds of grams of carbon are needed to count enough decaying beta particles.
Because this decay is constant it can be used as a “clock” to measure elapsed time assuming the starting amount is known.14C enters the dissolved inorganic carbon pool in the oceans, lakes and rivers.From there it is incorporated into shell, corals and other marine organisms.The absolute radiocarbon standard is 1890 wood, the OX-I standard has an activity of 0.95 of this wood.The definition of year “0”, “modern” or “present” is 1950, there is no real reason for this other than to commemorate the publication of the first radiocarbon dates.These newly formed 14C atoms rapidly oxidize to form 14CO..
Photosynthesis incorporates 14C into plants and therefore animals that eat the plants.
All radiocarbon ages are normalized to a 13C of -25‰ relative to PDB.
Calibration In the 1950s it was observed that the radiocarbon timescale was not perfect.
His first publication showed the comparisons between known age samples and radiocarbon age (Libby et al, 1949; Libby, 1952). For the first time it was possible to obtain ages for many events which occurred over the past ~50,000 years.
In 1960 Libby was awarded the Nobel Prize for chemistry for this contribution.
This means that it can be difficult to effectively clean the samples and remove enough contaminating carbon to obtain an accurate date.