Libby carbon dating
The method was developed by Willard Libby and his colleagues at the University of Chicago in 1949.
In 1960, he was awarded the Nobel Prize in Chemistry for this work.
The ultimate cause of carbon-14 variations with time is generally attributed to temporal fluctuations in the cosmic rays that bombard the upper atmosphere and create terrestrial carbon-14.
Whenever the number of cosmic rays in the atmosphere is low, the rate of carbon-14 production is correspondingly low, resulting in a decrease of the radioisotope in the carbon-exchange reservoir described above.
The relatively short-lived C taken into organic matter is also slightly variable. However, under about 20,000 years the results can be compared with dendrochronology, based on tree rings.
For the most accurate work, variations are compensated by means of calibration curves.
Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. In 1958 Hessel de Vries showed that the concentration of carbon-14 in the atmosphere varies with time and locality.
Expressed as a fraction of the contemporary level, they have been mathematically converted to ages through Improvements in measurement accuracy and the ever-mounting experience in applying carbon-14 dating have provided superior and more voluminous data with which to better answer Libby’s original questions.
It is now clear that carbon-14 is not homogeneously distributed among today’s plants and animals.
The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. C is the radioactive one, its half-life (time it takes to reduce its radioactivity by half) is about 5,730 years.
Atmospheric nuclear weapon tests almost doubled the concentration of Radiocarbon dating, also known as the C14 dating method, is a way of telling how old an object is. This makes it possible to tell the age of substances that contain carbon. Dates obtained are usually written as before present ('present' is 1950).