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Environment

Eyes in the Sky Look Back in Time

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Charles Q. Choi is a science journalist who has also written for Scientific American, The New York Times, Wired, Science, and Nature. In his spare time, he has ventured to all seven continents. The Fertile Crescent in the Near East was long known as "the cradle of civilization," and at its heart lies Mesopotamia, home to the earliest known cities, such as Ur. Now satellite images are helping uncover the history of human settlements in this storied area between the Tigris and Euphrates rivers, the latest example of how two very modern technologies---sophisticated computing and images of Earth taken from space---are helping shed light on long-extinct species and the earliest complex human societies. In a study published this week in PNAS, the fortuitously named Harvard archaeologist Jason Ur worked with Bjoern Menze at MIT to develop a computer algorithm that could detect types of soil known as anthrosols from satellite images. Anthrosols are created by long-term human activity, and are finer, lighter-colored and richer in organic material than surrounding soil. The algorithm was trained on what anthrosols from known sites look like based on the patterns of light they reflect, giving the software the chance to spot anthrosols in as-yet unknown sites.

ur-anthrosol-map1.jpg

This map shows Ur and Menze's analysis of anthrosol probability for part of Mesopotamia.

Armed with this method to detect ancient human habitation from space, researchers analyzed a 23,000-square-kilometer area of northeastern Syria and mapped more than 14,000 sites spanning 8,000 years. To find out more about how the sites were used, Ur and Menze compared the satellite images with data on the elevation and volume of these sites previously gathered by the Space Shuttle

. The ancient settlements the scientists analyzed were built atop the remains of their mostly mud-brick predecessors, so measuring the height and volume of sites could give an idea of the long-term attractiveness of each locale. Ur and Menze identified more than 9,500 elevated sites that cover 157 square kilometers and contain 700 million cubic meters of collapsed architecture and other settlement debris, more than 250 times the volume of concrete making up Hoover Dam. "I could do this on the ground, but it would probably take me the rest of my life to survey an area this size," Ur said

. Indeed, field scientists that normally prospect for sites in an educated-guess, trial-by-error manner are increasingly leveraging satellite imagery to their advantage. For instance, paleoanthropologist Lee Berger at the University of Witwatersrand in South Africa and his colleagues discovered Australopithecus sediba

, a 1.98-million-year-old relative of humans, with the aid of Google Earth

. The 3-D capabilities of the program—originally developed by a CIA-funded company that Google acquired—helped the scientists identify nearly 500 new caves for study from satellite images, which further research revealed had more than 25 fossil sites previously unknown to science. (Berger's 9-year-old son was the one who actually uncovered the first fossils when they reached the site, by literally stumbling over the bones

.) Paleontologists are also developing an artificial intelligence network to scan satellite images for new fossil sites

in the Wyoming desert. The computer program is a neural network

that imitates the working of the human brain, and is scanning maps and satellite imagery that include known fossil sites to learn what they look like, relying on factors like color. It then uses this experience to point out areas that might hold hitherto unknown fossil sites in the Great Divide Basin, a large stretch of rocky desert in Wyoming. Archaeology and paleontology have long been shovel- and pickaxe-dependent sciences, and will almost certainly stay so for the foreseeable future: Despite the occasional use of a backhoe or ground-penetrating radar, most digs simply lack the funding to bring anything they cannot carry in a bucket or the back of a pickup truck. But given the chance to use what once was classified military satellite imagery for free, it makes sense that researchers are leaping at the chance to prospect for sites using Google instead of boots on the ground. So what might such a trend suggest for the future? Archaeologists and paleontologists are already working to bring the extraordinary power of publicly available satellite and other mapping technologies to bear on the unexplored wilds of the world. But there may be a more interesting development in aerial archaeology: Dilettantes and hobbyists could use the technology to make their own discoveries from afar. After all, amateur astronomers make monumental finds all the time in space, such as alien solar systems

, and on Earth, mysterious mammoth structures spotted in China

have drawn both amateur and professionally trained analysts to publicly speculate over their nature. But as more amateurs swarm onto archaeological and paleontological sites, they may also be a risk that looters

will come in with them. Hopefully the curious and careful will be more numerous than the greedy and grasping. As Indiana Jones said about such historical treasures, "That belongs in a museum!"

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