How do you map the expansion of Earth's earliest civilizations? For years, researchers have tackled this daunting task on a settlement-by-settlement basis, searching for clues in mounds of earth throughout the Middle East.
But now, researchers have turned to satellite imagery to uncover a vast network of over 14,000 long-overlooked Mesopotamian settlements, spanning 8,000 years of ancient civilization. Their findings represent a monumental step forward for the fields of archaeology and anthropology, and suggest that an aerial perspective may hold the key to unlocking the mysteries of humanity's first major settlements.
A significant body of archaeological evidence suggests that the earliest civilizations arose in Mesopotamia, the geographic region that today comprises Iraq, northeast Syria, southeast Turkey and southwest Iran. The size and distribution of these settlements throughout the Mesopotamian landscape, however, has long remained something of a mystery.
Traditional archaeological techniques require researchers to search for evidence of these ancient civilizations up close, at the ground level. This is an excellent method for learning about individual settlements, but is a painstaking way to make sense of how these communities may have interacted with one another, or spread across the landscape over time.
That's where Harvard archaeologist Jason Ur and MIT computer scientist Bjoern Menze come in. By combining spy-satellite photos acquired during the 1960s with modern images of the Earth's surface, Menze and Ur have devised a new method of mapping patterns of human settlements at an unprecedented scale.
Ur and Menze recently used their new technique to map upwards of 14,000 previously overlooked settlements, distributed over 23,000 square kilometers of Mesopotamian landscape.
"Archaeologists knew of about 1,000 sites in this region previously, mostly the largest and highest ones," explained Ur in an interview with io9, "so it's quite a leap in terms of what we know."
The new method of aerial analysis relies on the detection of anthrosol, a distinctive type of soil that forms in the presence of long-term human activity. Anthrosols have a subtle but distinctive color, and are richer in organic matter than surrounding soils — a fact that archaeologists have been using for years to search for settlements at the ground level. But Ur and Menze took the search for anthrosols to the sky, with the help of multi-spectral satellite images.
Multi-spectral imagery, explains Ur, is useful for distinguishing different wavelengths of electromagnetic radiation, including those wavelengths that our eyes can't see:
A black and white photograph takes all of the wavelengths visible to us and blends them together. A color image shows them as combinations of red, green, and blue. Multispectral imagery... can see larger wavelengths like the near-infrared and beyond. The soils atop archaeological sites can be sensitive in both the visible and infrared ranges.
The beauty of Menze and Ur's new satellite technique is that it takes something archaeologists have been doing for years (seeking out settlements by searching for anthrosols), scales it up, and automates it; the fact that the satellite imagery is analyzed by an algorithm means that it takes the detection out of the hands of human operators, who, according to Ur, are slow and subjective.
Ur says he and Menze see their research as more than an academic exercise: "[This is] a way to make sure that government planners know to take [these settlements] into consideration when making decisions about future development and modernization, which can be quite destructive to the traces of the past," says Ur. Many regions of the Middle East, he explains, have been understudied by archaeologists, which puts them at risk of being wiped from existence altogether.
"We're hoping to put a lot of sites on the map in a hurry."
Ur and Menze's findings are published in the March 19th issue of Proceedings of the National Academy of Sciences.
Images via PNAS