Archaeologists Rewrite Timeline Of Bronze And Iron Ages

Writing in two articles in the forthcoming issue of the journal Science (Dec. 21), archaeologists from Cornell University and the University of Reading (England) and a physicist from Ruprecht-Karls-Universität Heidelberg (Germany) have given a new kind of precision to the timeline of the Bronze and Iron Ages in the Aegean and the Near East.

"Establishing this chronology means that the objects -- metalwork, furniture, woven textiles, and an alphabetic inscription found in a tomb in central Turkey -- were older than previously thought by some 22 years," said Peter I. Kuniholm, Cornell professor of art history and archaeology.

Among the artifacts found in the Midas Mound Tumulus at Gordion, the capital of ancient Phrygia, a site west of Ankara, Turkey, is a shallow, bronze bowl with a patch of beeswax on the rim carrying an alphabetical inscription. The inscription is a precursor to -- or contemporary with -- the earliest attested occurrences of the Greek alphabet. In addition to letter forms known from ancient Greek, there is a vertical arrow, known also from Etruscan inscriptions.

With the new chronology, the bowl now is independently dated circa 740 B.C., making its inscription as old as the oldest known artifacts on which the Greek alphabet appears: an oinochoe (a wine pitcher) from the Dipylon cemetery in Athens and a cup from Pithekoussai (now Ischia) in the Bay of Naples. The estimated dates of these pots previously had provided archaeologists with only an approximate date for these early alphabetic inscriptions. "The alphabet, which originated in Phoenicia at a time that is still disputed, was moving west at a rapid pace, traditionally thought to be by sea but now clearly by land as well. That's what this chronology shows: The alphabet was really catching on," says Kuniholm. Scholars believe that the birthplace of all Western alphabets, including the Greek and Roman, was Phoenicia (present-day Lebanon, Israel and Palestine). The oldest known Phoenician inscription was found in the Ahiram epitaph at Byblos, Lebanon, dating from about the 11th century B.C. Scholars think the alphabet was spread throughout the Mediterranean by traders who found the new shorthand an improvement over the syllabic scripts such as Linear B and cuneiform Hittite.

Kuniholm and his colleagues are using the science of both carbon dating and dendrochronology, dating through tree rings, to calibrate history. Their latest research involved carbon-14 analysis on 10-year slices -- that is rings covering 10 years of growth -- on wood from pine trees from the Catacik Forest in Turkey and from oak trees in Germany. By currently accepted models, the carbon-14 concentrations should have been identical in both the pine and the oak. And while the scientists discovered that this was true in general, they were surprised to find that for certain key periods, the Turkish pine appeared to be older than the German oak by as much as 17 years. "Those pieces of wood are the same tree-ring age, and they should have the same radiocarbon age, but they don't," says Kuniholm.

What happened, Kuniholm believes, is that the Turkish pine, growing in a warmer climate and at a lower latitude, absorbed less carbon-14 during documented periods of so-called solar minima -- prolonged cooling periods in the Northern Hemisphere, such as those in the eighth and ninth centuries B.C. and in the 15th and 16th centuries A.D. The German oak, which starts its growing season later in the spring than does the Turkish pine, absorbed measurably more amounts of carbon-14 during such cooling periods. "The trees are like a tape recorder of the radioactivity of the cosmos," Kuniholm said, "but they record only when they are growing."

Carbon-14, an isotope of the element carbon, is produced in the Earth's lower stratosphere by the collision of neutrons, produced by cosmic rays, with nitrogen. (An isotope is made up of atoms of the same element but with different numbers of neutrons.) During periods of high solar activity, the solar wind prevents charged particles from entering the atmosphere -- thus producing little carbon-14. However, carbon-14 production peaks during the solar minima, and it enters the Earth's troposphere as carbon dioxide-14 during the late spring in the Northern Hemisphere. By the following spring, the higher concentration of carbon in the troposphere is diluted. Thus, German oak, which grows late in the spring and summer, absorbs less carbon dioxide-14 than Turkish pine or juniper, which grows from the early spring to summer. "This is the first time scientists have been able to note a regional difference in tree rings of the same dendrochronological age," says Kuniholm. "Sadly, now, with all the carbon in our atmosphere, with the pollution we have from our cars and factories and energy facilities, the trees have all but given up providing many of these valuable signals."

Kuniholm's co-authors on the Science papers were Sturt Manning of the University of Reading, Bernd Kromer of Ruprecht-Karls-Universität Heidelberg, and Maryanne Newton, Cornell doctoral candidate. Research collaborators also include Marco Spurk, Universität Hohenheim, Stuttgart, Germany, and Ingeborg Levin, Universität Heidelberg, Germany. The concurrent Science articles are titled, "Regional Radioactive Carbon Dioxide Offsets in the Troposphere: Magnitude, Mechanisms and Consequences" and "Anatolian Tree Rings and a New Chronology for the East Mediterranean Bronze-Iron Ages."

The research was funded by the Institute for Aegean Prehistory, the National Science Foundation, the Malcolm H. Wiener Foundation, the Heidelberg Academy of Sciences and Germany's Federal Ministry of Educational Research.

Related Web sites:

Aegean Dendrochronology Project: http://www.arts.cornell.edu/dendro

A companion opinion piece in Science by Paula Reimer, Livermore Laboratories: http://www.calib.org/paula