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Time Keepers

A Research Team From Cornell University Has Developed the First Tree-Ring Chronology Covering the Middle East, Which Is Allowing the Precise Dating of Many Events From the Cradle of Civilization.


The Middle East is the cradle of civilization, but historians and archeologists have surprisingly few firm dates to tie to specific events. Written chronicles may tell how long a given king reigned, who preceded him and who followed, but they rarely contain information that allows a researcher to say, for example, "This happened in 532 B.C."

As a consequence, researchers have used radiocarbon dating and documents dated from their archeological context to develop three distinct chronologies of early civilization. But individual dates within those chronologies can vary by as much as 100 years. Wrong dates can have profound consequences in interpreting history.

Doing a historical study with a 100-year mistake would be like trying to understand America under Ulysses S. Grant "with the assumption that Russia was [simultaneously] ruled by Boris Yeltsin," said archeologist Aslihan Yener of the University of Chicago.

But help is on the way. A team from Cornell University has developed the first tree-ring chronology encompassing the Middle East, a development that could allow the dating of many events with a precision hitherto impossible. The new chronology produces dates "to the year," said Cornell archeologist Maryane Newton.

Their chronology, which now stretches from 2220 B.C. to 718 B.C. provides an unusual window into the dawn of the city-state. It indicates, for example, that:

* Logs used to build the inner chamber of the tomb of King Midas of the Phrygians were cut in 718 B.C.

* Timbers from a shipwreck that yielded a gold scarab with the name of Egypt's Queen Nefertiti were cut down in 1316 B.C.

* Juniper and cedar logs from the walls of a Middle Bronze Age palace at Acemhoyuk in Asia Minor--modern Turkey--were cut in 1752 B.C.

* Similar logs from the Warsama Palace at neighboring Kultepe were cut in 1810 B.C.

Because documents preserved on clay in those buildings provide links with the rulers of Assyria and Syria, Newton said, the new chronology provides important evidence toward the resolution of a century of debate over Assyrian and Mesopotamian chronologies.

The results also move back the date of the Late Bronze Age, a crucial period that encompassed the societies of the Minoans, Myceneans, Egyptians and Assyrians, by as much as 100 years.

The Cornell work demonstrates that one of the conventional timelines, the so-called High Chronology, "is clearly not sustainable," Newton said.

Dating with tree rings, formally known as dendrochronology, is an old and widely accepted technique. A chronology based on bristle-cone pines from the American Southwest now stretches from the present day to more than 2000 B.C., enabling archeologists to accurately date a wide variety of sites and artifacts from that region. Similar chronologies have been developed in other areas of the world.

The idea behind dendrochronology is simple. Every year under its bark, each tree lays down two new layers--one broad and light colored during the growing season, the other narrow and dark in winter when little growth occurs. The amount of new tissue varies each year, depending on average temperatures, rainfall and other factors, but all trees in a given region show the same relative amount of growth.

Cutting across the trunk of a tree reveals a distinctive pattern of dark and light bands, one pair for each year the tree lived. By lining up identical patterns from two trees whose life spans overlapped, researchers can extend the chronology as far forward and back in time.

The trick is finding a firm date for one or more rings so that a particular year can be assigned to each band. To do that, they look for rings with unusual growth--reflecting perhaps a known climatological event.

Newton, her mentor, archeologist Peter I. Kuniholm, and their colleagues collected wood and charcoal samples from 22 sites throughout the eastern Mediterranean to establish their chronology. They then used radiocarbon dating to provide approximate dates for important rings in the chronology.

But to tie it down firmly, they relied on evidence from perhaps the greatest catastrophe of the era--the eruption of the volcanic island Thera in the Aegean Sea. Ash from Thera dispersed in the upper atmosphere , causing summer to be cooler and wetter virtually worldwide.

Archeologists had long believed that the Thera eruption occurred around 1500 B.C., but University of Arizona scientists and others have dated it to 1628 B.C.

At about the same time in their tree-ring chronology, Kuniholm's group found an unusually narrow growth ring in wood from Porsuk, a site in central Turkey about 500 miles downwind from Thera where growth would have been curtailed by ash. Defining the ring for that year as 1628 B.C. nailed down their chronology. A second unusual growth ring in their chronology 470 years later then coincides with a volcanic eruption in Iceland, previously dated to 1159 B.C. based on European tree rings.

Other researchers are already taking advantage of the new timeline. Archeologists Hendrik J. Bruins, of the Ben-Gurion University of the Negev in Israel, and Johanes van der Plicht, of the University of Groningen in the Netherlands, recently reported new results dating the fall of Jericho, the city that, according to the Bible, Joshua and the Israelites sacked after wandering for 40 years in the desert.

Bruins and van der Plicht performed high-precision radiocarbon dating on charred cereal grains from the modern site of Jericho, Tell es-Sultan, and concluded that Jericho fell about 45 years after the eruption of Thera. They note that the cloud of dust and smoke emitted by Thera could have caused the biblical "darkness that can be felt" in Egypt that helped convince the pharaoh to let the Israelites leave their bondage.

Forty years of wandering in the desert, the researchers conclude, would have then put the Israelites in the vicinity of Jericho just about the time its walls fell.

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