Carbon dating test isotope of carbon dating
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.
The half-life is the time taken for an amount of a radioactive isotope to decay to half its original value.
Because this decay is constant it can be used as a “clock” to measure elapsed time assuming the starting amount is known.
This brings us to two reasons why a radiocarbon date is not a true calendar age.
The true half-life of 14C is 5730 years and not the originally measured 5568 years used in the radiocarbon age calculation, and the proportion of 14C in the atmosphere is not consistent through time.
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.
Photosynthesis incorporates 14C into plants and therefore animals that eat the plants.Three isotopes of carbon are found in nature; carbon-12, carbon-13 and carbon-14.Carbon-12 accounts for ~99.8 % of all carbon atoms, carbon-13 accounts for ~1% of carbon atoms while ~1 in every 1 billion carbon atoms is carbon-14.The main limitation of these techniques is sample size, as hundreds of grams of carbon are needed to count enough decaying beta particles.This is especially true for old samples with low beta activity.This method needs less than 1 mg of carbon and directly measures the abundance of the individual ions of carbon (14C, 12C and 13C).