Calibrated vs uncalibrated carbon dating
Radiocarbon dates are presented in two ways because of this complication.The uncalibrated date is given with the unit BP (radiocarbon years before 1950).
Then, by using the idea that the styles of objects evolve, becoming increasing elaborate over time, they could place them in order relative to each other - a technique called seriation.Other high profile projects include the dating of the Turin Shroud to the medieval period, the dating of the Dead Sea Scrolls to around the time of Christ, and the somewhat controversial dating of the spectacular rock art at Chauvet Cave to c.38,000 cal BP (c.32,000 BP) – thousands of years earlier than expected.Radiocarbon dating has also been used to date the extinction of the woolly mammoth and contributed to the debate over whether modern humans and Neanderthals met.These new techniques can have a dramatic effect on chronologies.With the development of a new method of cleaning charcoal called ABOx-SC, Michael Bird helped to push back the date of arrival of the first humans in Australia by more than 10,000 years.In this way large domed tombs (known as tholos or beehive tombs) in Greece were thought to predate similar structures in the Scottish Island of Maeshowe.
This supported the idea that the classical worlds of Greece and Rome were at the centre of all innovations.
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.
The second difficulty arises from the extremely low abundance of C, making it incredibly difficult to measure and extremely sensitive to contamination.
In the early years of radiocarbon dating a product’s decay was measured, but this required huge samples (e.g. Many labs now use an Accelerator Mass Spectrometer (AMS), a machine that can detect and measure the presence of different isotopes, to count the individual C atoms in a sample.
Radioactive decay can be used as a “clock” because it is unaffected by physical (e.g. For instance, the amount varies according to how many cosmic rays reach Earth.