# Status of Synchronisation of East Mediterranean Civilizations

The main problem of synchronisation is absolute dating, which is necessary to put the many existing links between civilizations of this period into an absolute time frame. In the current project however, these links should be evaluated on a more common basis. However, there are conflicting results concerning absolute dates depending on the methods used by the humanities and natural sciences, respectively.

The focus of interest is the dating of the volcanic eruption of Thera. Archaeologists date this event, which was the main reason for the loss of the hegemony of the Minoan culture, to be within the 16th/15th century BC, although there are different opinions. Warren and Cadogan date the eruption between 1550 and 1480 BC (Myers et al, 1992), Driessen and McDonald between 1550 and 1530 BC (Driessen, McDonald, 1995).

On the other hand, natural science dates this event to the 17th century using an increasing number of new methods. In addition, ice core examinations resulted in a date of 1645 ± 20 BC (Hammer et al, 1987). Dendrochronology, through the investigation of frost rings in trees as records of major volcanic eruptions (LaMarche Jr. et al, 1984), dates the eruption of Thera to 1628 BC. 14C dates also cluster towards such an early date. Table 1 presents all 14C dates available, which are in connection with the Thera event. Figure 6a presents the combined calibration of 61 samples and figure 2b 42 14C dates after the elimination of outliers, from the destruction layer of Akrotiri. Although the c2-Test shows, that not all the dates come from one event only, the time span for 1-ó lies between 1672 and 1631 BC, the 2-ó between 1690 and 1610 BC. Thus 14C dating strongly confirms the dendrochronological, but also the ice core date. Through the tree-ring calibration of 14C dates (figure 1), however, one should realize that dendrochronology and radiocarbon dating are not entirely independent methods. Some archaeologists have accepted this date and integrated into their chronology (Niemeier, 1995, and Betancourt, 1987).

The main criticism against the early dates is the reliability of dendrochronology, which is based on trees grown in North America, Germany and Ireland, for dating in the Eastern Mediterranean (Rohl, 1996). Recently there also seems to be a verification by the dendrochronology developed on Anatolian trees, exactly matching the other dendrochronologies (Kuniholm, 1996). The most important finding are some tree ring samples from Porsuk, only 840 km east of Thera. These samples have been combined with others to form a floating sequence of 1503 years, absolutely dated by parallelisation with other dendrochronologies from 2220-718 BC. Ring number 854 shows a real big anomaly. It is not a frost ring, but a ring with rather enhanced growth, but this can be explained geographically. When in North America the Thera ash cloud produced a significant frost, in Anatolia it resulted in heavy rain falls. This ring 854 must be from the year 1628 BC. Wiggle matching from 18 samples from different parts of this dendrochronology date this ring 854 to 1641+76 -22 BC.

For this project is of importance that Bietak (Bietak, 1995) discovered in Lower Egypt in the Hyksos settlement from Tell el´Daba pumice presumably deriving from the great eruption at Thera. Recently, the advocates of the conventional (lower) chronology are encouraged by the discovery of this pumice in strata which follow those of the late Hyksos palace recently unearthed at this site. Deposits associated with that palace contained fragments of fresco paintings of Minoan character closely resembling some of those found in Thera and dating from the period there immediately before the great eruption. From stratigraphical evidence these layers can be dated earliest to the beginning of the 18th dynasty, which means a date of about 1550 BC according to the Cambridge Ancient History Record (CAHR).

Figure 1 Sections of the tree-ring calibration curve relating a measured radiocarbon age to a calibrated date, relevant for the second millennium BC. (a) shows the range from 2500 to 1500 BC and (b) from 2000 to 1000 BC. The curves were generated from the 14C calibration program available from Oxford (Bronk Ramsey 1995), which is particularly versatile and easy to handle. The band width indicates the 1-s uncertainty in the calibration curve. Although there are only small "wiggles" in the curve, there are obviously sections where even a precise 14C/12C ratio measurement will lead to relatively large uncertainty in the calibrated age.

Fig.2a

Fig.2b

Figure 2 Combined Calibration for dates from the Akrotiri destruction layer, before (a) and after (b) elimination of outliers.

Although the c2 test fails in both cases, thus underlining that not all dates come from one event only, the following results are obtained: In case (a) 61 samples give a mean of 3365 ± 7 BP. By calibration two intervalls are received for the 1-s confidence intervall (that means with 68,2 % confidence), the first from 1730 to 1725 BC (with only 7% probability) and the second from 1690 to 1645 (with 93% probability). In case (b) 42 samples give a mean of 3339 ± 8 BP. That gives calibrated only one intervall for the 1-s confidence from 1672 to 1631 BC and one intervall for the 2-s confidence from 1690 to 1610. The little peak on the right side near 1550 BC lies outsides the 2-s intervall and is thus smaller than 5% of the whole distribution. That is why this peak is neglected by the calibration.

The problems arising with discrepancies in dating of the Thera eruption are closely linked with Egyptian chronology, and with the CAHR. There are three floating relative chronologies with absolute duration, one for the Old Kingdom, the Middle Kingdom and the New Kingdom. For each of them the list of kings with the time span of their rule is known. What is not known from the record is the absolute beginning and the duration of the intermediate times. As shown extensively by Woelfli (Woelfli, 1994, especially with his fig.10) calibrated 14C dates from the Old Kingdom are on the average 375 years older than after CAHR.

Many of the 14C dates from Egypt seem to have problems. Therefore, one of the main goals of this project is to repeat many datings with AMS under special precautions for the sample selection.

Selection of Samples

Among a variety of selection criteria for samples, two are particularly important: First, the samples should have a good archaeological context, which means that their position in the context should be known and the stratigraphy should be clear. Second, these strata or contexts should also contain well-defined and archaeologically datable remains.

Selection by Time

Because of the shape of the calibration curve not all segments are equally well suited for 14C dating. To show the problems in figure 2a and 2b two overlapping sections of the calibration curve are presented. The first ranges from 2500-1500 and the second from 2000-1000 BC.

Samples will only be taken from archaeological contexts belonging to "secure" segments of the calibration curve, where it runs reasonably steep and unambiguous. At that time, the new VERA AMS system should be ready for high precision (<0.5%) measurements. Multiple measurements of samples from "secure" sectors of the calibration curve should be carried out, thus reducing the uncertainty of the dates to a minimum.

The following time segments in the first half of the second millenium BC are for example at our disposal for high precision measurements: from 1960 - 1880, 1680 - 1620 and 1460 - 1400 BC.

In addition, if several radiocarbon ages are measured for a particular time period, "wiggle matching" to the corresponding section of the calibration curve may also lead to an absolute age assignment, if good relative chronologies are supplied. Thus also samples could be dated if they do not fall into the secure parts of the calibration curve.

Selection by Material

With charcoal there is in general the old wood problem. It may originate from wood which was already old when it was burnt, and thus deliver results which are too old. So we want in this project only - as far as available - concentrate on the dating of short-lived samples, such as burnt seeds or similar material. In contexts, which can be very well dated relatively or absolutely as in Egypt it is necessary to do so.

It will also be possible to consider dating of bones within this project, assuming that VERA has gained enough experience with bone dating, when this project comes into effect. Best results will be derived by using bones from short lived animals.

Collection of Samples

The Collection of samples from Egypt and different regions of the Aegean will be done by various collaborators of the project.

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