Satellite Views Reveal Early Human Settlements

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Scientists have unveiled a new technique for mapping early human settlements in Mesopotamia, the so-called “cradle of civilization” comprised of modern-day Iraq, northeast Syria, southeast Turkey and southwest Iran.

A pair of Harvard University anthropologists developed a way to measure mounds of athrosol, a type of soil formed by long-term human activity, in multi-wavelength satellite images.

Anthrosols are finer, lighter-colored, and richer in organic material than surrounding soil.

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“Soil discoloration is one of the characteristics of archaeological sites in this part of the world (alongside surface artifact density and mounding),” Harvard University anthropologist Jason Ur wrote in an email to Discovery News.

Scientists have been using anthrosols to locate settlement sites for 10 years, but were limited to ground observations and declassified black-and-white spy satellite imagery.

“Multi-spectral imagery opens up new possibilities for identifying ancient places because now we can look for these distinctive soil discolorations not only in the visible part of the spectrum (what the human eye seems as red, green, and blue) but also beyond the abilities of our eyes (the near-infrared and even larger wavelengths),” Ur said.

“The mounds that we find are entirely artificial creations on an otherwise relatively flat plain,” he added.

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Until the development of cement, building material was limited to mud bricks, which don’t last forever.

Eventually, the structures become unstable and must be leveled and rebuilt.

“If this process continues for centuries or millennia, settlements grow vertically,” Ur said, leading to massive buildups of decayed mud brick.

For example, the largest site, Tell Brak in northern Syria, contains about 8 million cubic meters of decayed mud brick and rises about 40 meters (131 feet) above ground.

“The sites are essentially large piles of anthrosols,” Ur said.

He and colleague Bjoern Menze, a computer scientist by training, used imagery from a sensor on NASA’s Terra satellite to detect the telltale sediments and a global digital terrain map made from radar imagery taken during a 2000 space shuttle mission to model the height and volume of mounded sites.

In all, the scientists mapped more than 14,000 sites, spanning 8,000 years of human settlement in northeast Syria. Some 9,500 of those sites showed significant elevations, a mass accumulation of 700 million cubic meters of collapsed architecture and settlement debris.

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“We’ve documented small areas of northern Mesopotamia at great cost in time and effort in the past,” Ur said. “This method finds a similar density of archaeological sites, just at a much faster rate and over the entire region.”

Ur and Menze say the technique can be used to build a comprehensive map of human settlements in northern Mesopotamia and beyond.

The research appears in this week’s Proceedings of the National Academy of Sciences.

Image (top): Comparison of multi-spectral satellite imagery and the distribution of surface artifacts at Tell Brak. The two analyses show are remarkably close correspondence. Credit: Menze and Ur/PNAS

Image (middle): Tell Brak, a mound in northeastern Syria, is an 8-million cubic  meter accumulation encompassing six millennia of human occupation. Credit: Menze and Ur/PNAS

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