In this book ice cores have been given pride of place in defining the timing of past climatic fluctuations. In extending the analysis to the rest of the world, and to broaden the investigation to other aspects of human prehistory, we have drawn on a wide variety of techniques for dating archaeological and geological objects and materials. These techniques have strengths and weaknesses that need to be spelt out when trying to build up a coherent picture of the past.

Experts working in a particular field will be well aware of the limitations of any particular technique they are using. But, to the outsider, the bewildering array of methods used and the apparently contradictory results they produce can lead to considerable confusion. The reasons for this complexity are not hard to find. Different methods produce different dates for events, partly because of differences in what is being measured and partly because of the inherent limitations of any given methodology.

RINGS AND LAYERS

The most reliable method of dating ancient objects, materials and events is to use either annual tree rings or undisturbed seasonal sediment layers that have been deposited at the bottom of lakes or, in special circumstances, the oceans (e.g. Cariaco Basin, Venezuela; Haug et al., 2001). In the case of tree rings it has been possible to construct a series of ring widths for western Europe that extends back over 11 000 years (11 kyr; Kromer & Spurk, 1998).