Wednesday, July 29, 2015

The Fall of a Civilization

Fig.1. Bronze head of a king, most likely Sargon of Akkad. 

Around 4,300 years ago, Sargon of Akkad ruled what was considered to be the world’s first empire. The prosperity of the Akkadian Empire, which relied on the fertile soils between the Tigris and Euphrates rivers, collapsed abruptly almost 200 years later. Scientists now hypothesize that Sargon’s empire fell to a dramatic shift in the climate, which dried up Akkadian's rain-dependent agricultural systems. A recent study published in the journal Quaternary Science argues that this Mesopotamian empire was only one of several ancient civilizations affected by sudden climate variability.

The Cradle of Civilization

A team of international scientists led by researchers at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science studied Mesopotamian climate records from the last 13,000 years. This time span encompasses the Holocene, which began after the last ice age approximately 11,7000 years ago, and marks the development of human civilization as we know it. Although previous palaeoclimatology work with sediment cores and stalagmites showed significant climatic variation during the Holocene, this study used both archaeological and geological records to understand ancient weather.

Lead author Arash Sharifi, a Ph.D. candidate at the University of Miami, and his colleagues examined a peat bog core from northern Iran to create a record of wet and dry conditions in Mesopotamia. These cores are often used to show local plant biodiversity, but they also show fluxes in dust found high in the atmosphere. Episodes of heavy atmospheric dust can be associated with much drier conditions and therefore act as a good proxy for sudden climate shift in ancient times.

Sharifi et al. used shits in atmospheric dust flux to determine that the early Holocene was largely wet, as opposed to the drier conditions seen today. They also found that at least six episodes of high atmospheric dust levels coincided with rapid periods of temperature and precipitation change, as seen in previously studied ice core and stalagmite records. These episodes of drier conditions corresponded to archaeological accounts of multiple socio-economic and cultural transitions due to drought. Such transitions included the fall of the Akkadian Empire in 2154 BCE, the end of the Third Dynasty of Ur in 2004 BCE, the conquering of the Parthians in 224 CE, the demise of the Sasanians in 651 CE, and the fall of several other empires in ancient Mesopotamia and western Asia.


Fig.2. Map of Mesopotamia with ancient cities in modern-day states 
(Credit: Coran tek-en)

Many Records, One History

Although Sharifi et al. do not believe drought or dust to be the only factor in the collapse of a civilization, they argue that climate variability significantly affected these societies and should be considered. As the ancient world transitioned from hunting and gathering to more agriculturally-based societies, precipitation and temperature would have played a large role.

Similar and more recent patterns can be seen around the world. The Mayan civilization collapsed around 900 CE and analyses of sediment cores and stalagmites documented a much drier period between 800 and 1000 CE. Even more recent and localized was the abandonment of a valley in Syria by the Ottoman Empire. Although bureaucratic mismanagement has been cited, some believe that drought may have been the main cause.

These environmental records are powerful on their own, but together with historical and archaeological data, they paint a nuanced picture of human history. If the rise and fall of human civilization is dependent upon weather, such studies provide lessons into how we can prepare for a world with more climate variability than ever.




References:
Cullen, H. M., et al. (2000, April). Climate change and the collapse of the Akkadian empire: Evidence from the deep sea. Geology, 28 (4): 379-382. Retrieved from: http://geology.gsapubs.org/content/28/4/379.full.pdf+html

Sharifi, A., et al. (2015, August). Abrupt climate variability since the last delaciation based on a high-resolution, multi-proxy peat record from NW Iran: the hand that rocked the Cradle of Civilization? Quaternary Science Reviews. doi: 10.1016/j.quascirev.2015.07.006



Glossary

climate variability
Patterns in the climate (warmer or colder temperatures, more or less precipitation, etc.) that can occur over decades.
Holocene
A geological epoch that began around 11,700 years ago, after the Pleistocene. The Holocene marks an interglacial period, which is an interval of warmer global average temperatures that separate glacial periods.
palaeoclimatology
The study of climate variation in Earth’s history. Palaeoclimatologists use proxy records, such as sediment cores, ice cores, tree rings, fossils, and more to understand ancient climate patterns.
peat bog
A wetland terrain dominated by deposits of dead plant material. The layered accumulation of decayed plant material is an excellent record of precipitation over time.

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