ITHACA, N.Y. -- A team of researchers at Cornell University has identified the exact year that logs were cut at an archaeological site in Turkey, a finding that has major implications for understanding the history of the Greeks, Egyptians and other ancient civilizations.
Reporting in the journal Nature (June 27), Peter I. Kuniholm, Cornell professor of the history of art and archaeology, with other researchers in the university's Aegean Dendrochronology Project and at the universities of Heidelberg and Reading, have constructed a tree-ring sequence spanning 1,503 years from the ring growth patterns preserved in wood and charcoal samples at 22 sites throughout the eastern Mediterranean. They identified this exact "window," from 2200 B.C. to 718 B.C., by analyzing variations in the width of annual tree rings (which are altered by changes in climate and moisture) from the wood and charcoal remains of ancient tombs, gates and buildings unearthed at these sites.
Using dendrochronology techniques they have perfected along with radiocarbon dating, the researchers were able to determine the exact year that some of those logs were chopped down. They report that logs used to build the inner chamber of the Midas Mound Tumulus, a massive tomb named for King Midas of the Phrygians and located at the Gordion archaeological site, were cut in 718 B.C.
"That is not plus-or-minus anything; it is a date 'to the year,'" said Cornell doctoral student Maryanne Newton, one of the Nature article's coauthors. "That level of precision, based on the fact that trees put on a single growth ring per year, is unique."
The researchers supplemented their dendrochronology work with radiocarbon "wiggle-matching," a process in which the radiocarbon profiles of the timbers are superimposed on a calibrated time scale and moved until the lines match up, and their knowledge of an earlier climatic event.
Previous research has shown that the major second millenium B.C. eruption of Thera, a volcanic island in the Aegean Sea, had global effects that likely influenced climate patterns as far away as the western United States. Volcanic ash from Thera blocked the sun and caused cooler, wetter weather conditions worldwide. Rings from American bristlecone pine trees revealed extensive frost damage attributable to the eruption.
But in the desert conditions of the Near East, Thera had the opposite effect: it spurred massive growth. Reduced exposure to sunlight and increased soil moisture led to tree rings in juniper, cedar and pine samples from Porsuk, a site in central Turkey, that were three to eight times wider than normal. Porsuk is about 840 kilometers downwind of Thera.
Archaelogists had long believed the Thera eruption had occurred around 1500 B.C., but more recent studies have strongly suggested the eruption occurred earlier, in 1628 B.C.
The "Porsuk event," as Newton calls the growth spurt in the Porsuk trees, was dated to 1628 B.C. -- lending further evidence that this was the year of the Thera eruption.
The findings reported by the Cornell team move back the Aegean Late Bronze Age by as much as a century. This age has long captured the popular imagination, Newton said, because it encompassed such cultures as the Minoans, Mycenaeans, Egyptians and Assyrians -- sophisticated civilizations that have been depicted in countless works of classical literature and film. The new chronology also has implications for historical accounts concerning such figures as Queen Nefertiti and Akhenaten, the Egyptian pharaoh.
The researchers determined that wood from a shipwreck containing a gold scarab inscribed with the name of Queen Nefertiti was cut down in 1316 B.C. The jewelry would not have been made until Nefertiti was queen, so the timber confirms that she held the throne by then -- which supports earlier historical findings.
Elsewhere, juniper and cedar logs from the walls of the Middle-Bronze-Age palace at Acemhöyük were determined to have been cut in 1752 B.C., and the Warsama Palace at Kültepe contained logs cut in 1810 B.C.
"Because documents preserved on clay in these buildings provide links with rulers from Assyria and Syria," the authors write, "the new fixed dendrochronology provides important evidence towards the resolution of a century of debate over Assyrian and Mesopotamian chronology."
To visualize such chronologies, one need only visit the Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology, located on the ground floor of Cornell's Goldwin Smith Hall. Pinned on the walls of a narrow lab cluttered with microscopes and maps, books and statues, computers and cabinets filled with charcoal samples, are long colored strips of paper depicting various chronologies. One orange strip on the wall runs from circa 500 B.C. to 50 A.D.; a blue strip pasted below begins at 362 A.D. and stretches around the corner to the present. Such simple displays belie the sophisticated technologies that are used at this and other dendrochronogy labs around the world to date ancient artifacts.
Cornell's dendrochronology lab is funded by the National Science Foundation and National Endowment for the Humanities and is the headquarters for the Aegean Dendrochronology Project. The project's ultimate goal is to connect early chronologies like the one described in Nature to the present, to create an "absolute chronology." By way of explanation, Newton offers this scenario:
"You go to a forest today and take a sample from a tree that you know grew to 1996. By counting 200 rings, you know that the tree is 200 years old and started growing in 1776. Then, you compare the pattern of its rings with those from a piece of wood from a building you know was built in 1860. You keep doing the same with earlier and earlier samples of wood."
While the researchers stress that they have not yet achieved an absolute chronology, they believe their latest findings have brought them considerably closer and will enhance their understanding of the relationship between pivotal cultural events of the past and present.
"Often the different dating systems which have been used in interpreting the history and archaeology of the Near East have had profound effects on how we understand cultural interactions," Newton said, "such as the rise and fall of the Minoan, Mycenaean and Greek civilizations; event-based histories, like the Trojan War and the Exodus; and social evolution, like the Neolithic Revolution and the formation of states. We must determine the absolute age of these historic and prehistoric processes, as well as their chronological relationship, in order to appreciate fully the implications of the past for modern society.
"What we announce in Nature is the beginning of the process of bringing some order to our understanding of the cultures and histories of our shared past."