Dendrochronology and carbon 14 dating
Aside from cross dating, the archaeologist faced with material in a site having no literate chronological evidence of its own has two other ways of dating his material. Relative dating merely means the relation of the date of anything found to the date of other things found in its immediate neighbourhood.
As has already been described, this method also plays a part in cross dating. The archaeologist observes the accumulation of deposits in a gravel pit, a peat bog, in the construction of a barrow, or in accumulated settlements in a tell, and, like the geologists who introduced the principles of stratigraphy in the late 18th and early 19th centuries, he can see the succession of layers in the site and can then establish the chronology of different levels of layers relative to each other.
When he is dealing with ancient history and prehistory, he is making a contribution of the greatest importance and often one that is more important than that of purely literary and epigraphical sources.
For the prehistoric period, which now appears to stretch from 2,000,000 years ago to about 3000 , archaeological evidence is the only source of knowledge about human activities.
In the excavation of a great tell like Ur or Troy the relative chronology of the various levels of occupation is the first thing to be established.
Some archaeologists, even until quite recent times, have mistakenly supposed that depth below ground level is itself an indication of antiquity.
Even when the absolute dates are available, we have to supplement the information with relative dating.
Second, there is a need for interpretive analysis of the material from which artifacts were made.
It is also now possible, entirely on a petrological basis, to study the prehistoric distribution of obsidian (a volcanic glass used to make primitive tools).
In the third place, the archaeologist, having dealt with the material of his artifacts by classification and taxonomy, and with its physical nature by petrology and metallurgy, turns to the remaining information he can get from his colleagues in the natural sciences.
Following the revolutionary discovery of radioactive carbon dating, other physical techniques of absolute dating were developed, among them The last and most important task of the archaeologist is to transmute his interpretation of the material remains he studies into historical judgments.
When he is dealing with medieval and modern history he is often doing no more than adding to knowledge already available from documentary sources: but even so his contribution is often of great importance; for example, in relation to the growth and development of towns and the study of deserted medieval villages.