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.
"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.
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.