Petrie's sequences were later adapted, even by himself. Petrie had placed white-crossed line ware in the period from SD 31 - 34, but later study has shown that this type of pottery may be dated to considerably later in the sequence. Petrie came to the conclusion that his SD 76 was not predynastic but was in fact the beginning of the First Dynasty. Further study has revealed, however, that the beginning of the historic period actually correlates with Petrie's SD 63.

At the beginning of the studies of the Predynastic Period, certain names were used to describe certain cultures, based on the site at which they were first discovered. Thus the Amratian culture was named after el-Amra near Abydos, the Gerzean culture after el-Gerza near the Fayyum depression. The earlier division of the Amratian and Gerzean has now been largely superseded by the terms Naqada I and Naqada II, which reflects the fact that these are really two stages of a contiguous culture. This system has more recently been expanded to include a further subgroup called Naqada III according to the research of the German scholar Werner Kaiser.

Excavations and surveys of the Predynastic Period continue to refine our knowledge. The relative dating which Petrie introduced for the Predynastic Era has been supplemented by the use of scientific dating methods including Carbon 14 dating and thermoluminescence.

Above is a graph that illustrates the relationship between how much Carbon 14 is left in a sample and how old it is.

Carbon 14 or radio-carbon dating was discovered during the Second World War and is based on the fact that all living things contain a relatively constant amount of an unstable isotope of Carbon, known as Carbon 4. At death, intake of Carbon 14 into the bodies of living things ceases, and that which remains in the body begins to decay to the stable Carbon 12 at a constant rate. The half life of Carbon 14 is 5730 years, which means that it takes 5730 years for half the Carbon 14 isotope to decay. By studying the relative proportion of the radioactive isotope remains in the body it is possible to establish the length of time since death. The older a sample is, however, the more likely it is to be contaminated and the more likely an incorrect dating will be given.

Another important scientific dating method was discovered at the University of Wisconsin during the 1960's. This was a technique called thermoluminescence dating. Scientists noted that all clays contain radioactive particles in the minerals making up the structure of the clay, which dissipate when the pottery is fired. As time goes by, the minerals such as quartz begin to accumulate radioactivity which is trapped in the crystalline lattice of the minerals. When the baked clay is reheated to about 500C, it is possible to measure the radioactivity which is released as light. Theoretically, it is possible to calibrate the number of years elapsed since the original firing. There are, however, many technical limitations to this method of dating, most importantly whether the sample has been contaminated by other material. Carbon 14 and thermoluminescence dates have given actual dates to the Sequence Dating system, and enabled us to look at the continuity of the Predynastic Period in more concrete terms.

[If you have a JAVAscript enabled browser:]
More about Carbon 14 dating
More about Thermoluminescence.
[If not, go to "Next"]