In radiocarbon dating

By using dead trees of different but overlapping ages, you can build up a library of tree rings of different calendar ages.

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between 2940BP and 3060BP for the measurement 3000 -30BP).

A slightly different method is now more often used which is called the `probability method'.

These values should correspond exactly to normal historical years BC and AD.

The term cal BP means the number of years before 1950 and can be directly compared to calendar years.

The wood in these rings once laid down remains unchanged during the life of the tree.

This is very useful as a record of the radiocarbon concentration in the past.

This plot shows how the radiocarbon measurement 3000 -30BP would be calibrated.

The left-hand axis shows radiocarbon concentration expressed in years `before present' and the bottom axis shows calendar years (derived from the tree ring data).

There are two main methods used for calculating age ranges from the calibration curve: The first method to be employed was called the `intercept method' because it can be done by drawing intercepts on a graph.

This method will tell you the years in which the radiocarbon concentration of tree rings is within two standard deviations of your measurement (e.g.

For older periods we are able to use other records of with idependent age control to tell us about how radiocarbon changed in the past.

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