An Example of Hard-Water Error in Radiocarbon Dating of Vegetable Matter

THE hard-water effect is a recognized source of error in radiocarbon dating. It causes ages to be over-assessed and arises when the material to be dated, such as mollusc shell or plant, synthesizes its skeleton under water and so uses bicarbonate derived in part from old, inert sources. It is usually stated that the maximum possible error is equivalent to the half-life of 14 C, 5,570 yr (Libby scale), but it rarely amounts to as much as this. Moreover, in an isolated dating it is not only impossible to evaluate, but even to know whether there is any over-estimation, but if the sample consists of tree wood, or the leaves, twigs or seeds of wholly terrestrial plants, then it can be assumed that no hard-water error is present.