Radioactive decay and carbon dating
In the 19th and early 20th century incredibly patient and careful archaeologists would link pottery and stone tools in different geographical areas by similarities in shape and patterning.
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.
From these records a “calibration curve” can be built (see figure 2, below).
A huge amount of work is currently underway to extend and improve the calibration curve.
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.
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.
This is affected by solar activity and the earth’s magnetic field.
This supported the idea that the classical worlds of Greece and Rome were at the centre of all innovations.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.Radiocarbon dates are presented in two ways because of this complication.The uncalibrated date is given with the unit BP (radiocarbon years before 1950).