Debating Dendrochronology THE DENDROCHRONOLOGY DEBATE Peter James discusses the quest for an absolute chronology for the ancient Aegean.

very archaeologist’s dream is a century date for the tomb. the Bronze Age explosion of Thera, dating technique which can The problem, however, has always ostensibly supported by an anomalous date finds to a precise year, been to peg this ‘Gordion Master amount of sulphuric acid in the Green- E and of all available methods Sequence’ precisely in time. Ideally, land ice layer dated to c. 1625 BC. Since dendrochronology comes nearest. In an dendrochronology works by counting then particles of volcanic glass have ideal case bark will still be preserved and back the rings on living trees, then been found in this layer, but analysis dendrochronology can tell us the exact matching their growth patterns with showed they are not from Thera. Now, year when the wood was felled. But recent dead trees and so on. Unfortu- we are told with the new dating that while this might work well for prehis- nately, Kuniholm and his team are far the growth anomaly in Anatolia conve- toric posts or firewood, matters are not from completing an ‘absolute’ den- niently matches c. 1645 BC, the other so easy for artefacts where carpenters drochronology back to the Iron Age. peak of Greenland sulphuric acid and sculptors have shaved off an The continuous sequence only goes favoured by high chronologists. A scep- unknown number of tree-rings. For this back to AD 362, while between that tic might wonder how much the quest reason dendrochronology usually only date and Midas’ time there are only for a precise date for Thera (the ‘holy offers a terminus post quem, a date after patchy sequences. As there is no way of grail’ of the lab boys) is driving research, which the artefact was made. providing an exact date for the Midas as much as the simple desire to sharpen All the same, the fact that den- tomb from history, radiocarbon has up Aegean dendrochronology. drochronology deals in real, exact cal- been turned to for an alternative Dating a tree-ring sequence is one endar years makes it more ‘tangible’ answer. Over the years numerous sam- thing; using it to provide actual dates than radiocarbon, which can only ples from the Gordion master sequence for archaeology is another. Unfortu- express dates as a broad range in terms have been radiocarbon dated at Heidel- nately, Kuniholm’s team have made of statistical probability. To know that berg University. Kuniholm’s first stab at some premature announcements which the last tree-ring in an artefact dates to interpreting these was to lower the date subsequent work has shown to be 899 BC is far more rewarding than of the tomb (and all the attendant cul- invalid. A date of 1305 BC for the Late learning that it grew sometime between ture) to c. 547 BC. Later tests raised this Bronze Age shipwreck of Uluburun (off 1020 BC and 830 BC (at 95.4% proba- date massively to c. 757, and in 1996 south-western Turkey) was trumpetted bility). One reason for the vagueness in the improved calibration curves again as confirmation of the generally radiocarbon dating is that the amount changed the date - to c. 718 BC. accepted chronology of the Late Bronze of carbon 14 produced in the atmos- Most recently - in two papers in last Age. In the recent Science paper it was phere (and hence absorbed by living December’s Science journal - the date virtually retracted. (The sample used organisms) has not remained constant. has been slightly raised again, to c. 740 was badly gnarled and twisted.) It is dendrochronology that has pro- BC. This time a large number of new Another date of 1621 BC for a wooden vided the key to this puzzle: by measur- radiocarbon tests were made on trees bowl from the Shaft Graves at Mycenae ing amounts of C14 in well-dated belonging to the upper and lower ends has been categorically withdrawn. (The tree-rings we can calibrate radiocarbon of the Gordion sequence. When ‘wig- rings were never properly measured.) results. Hence the double importance of gle-matched’ against the central Euro- While the fact has not been advertised a sound dendrochronology. pean dendrochronology, the dates from by Kuniholm and his colleagues, these The hopes of East Mediterranean the two ends were found to be offset by are the only two results so far declared archaeologists presently rest on the over two decades (compared to the for the Aegean Late Bronze Age, and work of Professor Peter Kuniholm and number of rings). The conclusion both have proved to be faulty. For the his Cornell University team, who, for reached in the Science articles is that the same period, dates for a number of Ana- many years, have been working on a upper dates should be preferred, raising tolian sites have been announced in dendrochronology for the ancient the whole sequence by 22 years. As for newsletters, but the results from only Aegean and Anatolia. The Aegean Den- the offset, it is explained by regional one have been fully published and drochronology Project has had some variations in the amounts of C14 - a these are clearly anomalous for the major successes. In the late 1950s Amer- possibility that has long been suspected. standard chronology. The salutary expe- ican archaeologists working at Gordion To use C14 dates calibrated by one tree- rience of Uluburun and Mycenae means excavated a spectacular royal burial, ring sequence (central Europe) in order that large question marks will remain believed to be the tomb of the famous to fix in time another (Anatolia), and over the other Anatolian sites until they Phrygian king Midas. (Though we know then to use that sequence to modify our are formally published for scrutiny. him best from Greek legend, Midas was Peter James wider understanding of C14 behaviour, About chronology-building Sir Mor- is a specialist on a real king, mentioned in Assyrian is clearly a perilous exercise. Yet the timer Wheeler once remarked ‘we ancient Near East- records of the late 8th century BC, and team may well be right in their have...been preparing time-tables; let us ern chronology the tomb could well be his.) It proved Solomonic judgement in favour of the now have some trains’. With respect to and principal to be a gift to dendrochronology. older Gordion results. The lower ones the time-tables, the work of the Aegean author of Underneath a huge earth mound, the fall largely in the 8th century, which Dendrochronology Project has been Centuries of small building forming the tomb con- has long been known as the beginning steady and apparently meticulous. As Darkness (1991; sists of large juniper logs with the bark of the ‘radiocarbon disaster area’ - a flat for the trains, some have already been see www. still present. One log contained as many stretch of the calibration curve stretch- derailed. Precision in archaeological dat- centuries.co.uk). as 918 rings and the group, taken ing from about 800 to 400 BC. ing is a desideratum, but it is not together, allowed Kuniholm to establish Other aspects remain worrying, achieved by having a highly accurate a sequence going back 1026 years. Next, however. The confident pronounce- time-table alone. It needs equal preci- the pattern of the earliest rings was ment that a firm chronology has now sion in the selection of high-quality found to overlap with the last rings of been achieved sounds disconcertingly samples from contexts with impeccable, another long sequence from Porsuk in like the claims made in 1996 (in and fully published, credentials. We still southern-central Turkey. Together they Nature). Then, the dating allowed the have a long way to go before the ‘dream span 1503 years - from the Middle team to match a tree-ring period of ticket’ of Aegean/Anatolian den- Bronze Age down to the assumed 8th- abnormal growth with a ‘high’ date for drochronology is fully realised.

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