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AGU Chapman Conference: “They walked away”

Leilan Lower Town 1991 Kite.jpgAt the AGU Chapman conference today, Yale archaeologist Harvey Weiss took the prize for an abrupt climate change picture worth a thousand words. Excavating an Akkadian palace in Tell Leilan, Syria, in 2006 and 2008, Weiss’s team found one room with a grain storage vessel smashed on the floor. Lying next to it were a standard litre measure used for rationing grain, and the tablet on which a bureaucrat had been recording the rationing. The artifacts date from about 2190 B.C., when cities and towns of the Akkadian empire in Mesapotamia were being abandoned en masse as the region suffered crushing drought.

“This site is the Pompeii of ancient Mesapotamia,” says Weiss. “They walked away.”

Weiss reviewed evidence that a rapid change in storm tracks in the North Atlantic – yet to be satisfactorily explained – dried out the Tigris and Euphrates valley 4,200 years ago. And that valley wasn’t alone. Around the same time, deflection of the Indian Monsoon hit the Nile with a drought, and Egypt’s Old Kingdom went down. The extreme events are also mirrored in North America from New Jersey to the Yukon. In a separate talk today, glaciologist Lonnie Thompson showed a new ice core data* from Huascar√°n in Peru, the highest tropical mountain, with a huge spike in dust deposition around this time. The dust probably blew off an aridifying West Africa, Thompson says.

As it turns out, the Egyptian and Mesapotamian civilizations devastated by the abrupt changes had arisen in the wake of a similar pattern 1,000 years before. Thompson reeled off theories about this ‘5.2 kiloyear’ event involving everything from the onset of the El Nino-Southern Oscillation cycle to a meteoric impact.

By radiocarbon-dating more than 50 items from the palace, Weiss has pinned down the exodus there with unusual accuracy. His dates have as little as 6 years’ error rather than the customary 130 years or more. He challenged the palaeoclimatologists gathered in Columbus to start coming up with more worldwide records of recent change that share this high level of certainty. By piecing together climatic events from high-resolution records, scientists might come up with the source of the ancient catastrophes.

Anna Barnett

Image: Tell Leilan, northeast Syria: residential area of 90-hectare city abandoned around 2200 BC during a period of abrupt climate change. Courtesy of Harvey Weiss.

*This post has been corrected with the word “data” inserted.


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