It may be used to date a wide range of natural and man-made materials.

Fossils may be dated by taking samples of rocks from above and below the fossil's original position.

From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events.

by Tas Walker A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.

The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.

A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will spontaneously change into a different nuclide by radioactive decay.

The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.

Measurements should be taken on samples from different parts of the rock body.

This helps to counter the effects of heating and squeezing, which a rock may experience in its long history.

It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place.

By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.

For example, a geologist may examine a cutting where the rocks appear as shown in Figure 1.