Chemistry of carbon dating
The calibrated date is also presented, either in BC or AD or with the unit cal BP (calibrated before present - before 1950).
The calibrated date is our “best estimate” of the sample’s actual age, but we need to be able to return to old dates and recalibrate them because new research is continually used to update the calibration curve.
This method requires less than 1g of bone, but few countries can afford more than one or two AMSs, which cost more than A0,000.
Australia has two machines dedicated to radiocarbon analysis, and they are out of reach for much of the developing world.
The rate of decrease is predictable and can be described with some accuracy, increasing our ability to perhaps date the biological events of our planet.
Carbon 14 is produced in the upper atmosphere when cosmic radiation from space interacts with nitrogen gas, converting nitrogen 14 to carbon 14.
Radiocarbon dates are presented in two ways because of this complication.
The uncalibrated date is given with the unit BP (radiocarbon years before 1950).
Because of this, radiocarbon chemists are continually developing new methods to more effectively clean materials.
In 2008 we could only calibrate radiocarbon dates until 26,000 years.
Now the curve extends (tentatively) to 50,000 years.
Professor Willard Libby produced the first radiocarbon dates in 1949 and was later awarded the Nobel Prize for his efforts.
Radiocarbon dating works by comparing the three different isotopes of carbon.
Carbon 12 is the stable variety, radioactive Carbon 14 has a half life of just under 5800 years.