How old trees and ancient wood are helping rewrite history explained by tree-ring lab director

Cornell archaeologists are rewriting history with the help of tree rings from 900-year-old trees, wood found on ancient buildings and through analysis of the isotopes (especially radiocarbon dating) and chemistry they can find in that wood.

By collecting thousands of years worth of overlapping tree rings, with each ring representing a tree's annual growth, the researchers have created long-term records in the eastern Mediterranean that allow them to precisely date such seminal milestones in history as when Hammurabi, "the law-giver," reigned, when the massive Santorini volcanic eruption occurred, and the timelines of the Bronze and Iron ages, as well as many more recent events.

Sturt Manning, director of the Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology at Cornell, summarized his work for Cornell council members and trustees, Oct. 19 in Statler Hall. Dendrochronology is the science of comparing growth patterns in tree trunks to date past events or climate changes. Cornell's dendrochronology laboratory now holds more than 40,000 tree-ring samples, including many from the eastern Mediterranean.

Trees of the same species from the same geographical area have fairly similar ring patterns, Manning said, because they are exposed to similar climatic conditions. By starting with living trees and then finding samples from slightly older trees used in buildings and still older trees from more ancient sites, archaeologists have been able to overlap tree-ring data to create chronologies that date back thousands of years.

Radiocarbon dating, statistical analysis, researchers' trained eyes and prior knowledge of events in the area are then used to match new samples with tree-ring chronologies from the same area. Manning and his staff in the lab have used such techniques to verify, for example, the likely origins of a Circle of Rembrandt painting (referring to an elite group of students that worked directly with the artist). He showed that the oak board of the painting came from the same tree as the board of another painting, whose origins are known and which hangs in a museum in Krakow, Poland.

Similarly, scholars have debated for more than 150 years about the dates of the ancient civilizations of the Babylonians, the Assyrians and the lifetime of Hammurabi, the Babylonian king who helped create the oldest set of written laws. Mainstream scholars have proposed dates for his reign that differ by 300 years.

"You can't do history if you have a difference of 300 years or so," said Manning. "That would place George Washington as a contemporary of some person living right now. ... You'd get entirely the wrong historical reconstruction if you didn't have the dates sorted out."

Using ancient beams from palaces of known contemporaries of Hammurabi, Cornell researchers combined radiocarbon dating techniques with dendrochronological evidence to date Hammurabi to around 1792 B.C., Manning said.

Similar techniques used on wood buried beneath volcanic ash allowed Manning and others to date the Santorini volcanic eruption, one of the largest in the last 10,000 years, as most likely occurring in the late 17th century B.C., 100 years earlier than previously believed. The discovery may rewrite the late Bronze Age history of Mediterranean civilizations, he said.

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