SAN JOSE, CALIFORNIA—What do the Sahara desert and the Amazon rainforest have in common? Until recently, archaeologists would have told you they were both inhospitable environments devoid of large-scale human settlements. But they were wrong. Here today at the annual meeting of the AAAS (which publishes Science), two researchers explained how remote sensing technology, including satellite imaging and drone flights, is revealing the traces of past civilizations that have been hiding in plain sight.

“Although [the Amazon and Sahara] seem so different, a lot of the questions are actually very similar,” says David Mattingly, an archaeologist at the University of Leicester in the United Kingdom. He studies a culture known as the Garamantes, which began building a network of cities, forts, and farmland around oases in the Sahara of southern Libya around 1000 B.C.E. The civilization reached its peak in the early centuries of the Common Era, only to decline after 700 C.E., possibly because they had tapped out the region’s ground water, Mattingly explains.

Many Garamantian structures are still standing in some form or another today, but very few have been visited by archaeologists. It’s hard to do fieldwork in the hot, dry, remote Sahara, Mattingly explains. “And that relative absence of feet on the ground leads to an absence of evidence” about the Garamantes and other cultures that may have thrived before the Islamic conquest of the region. But because many Garamantin sites haven’t been buried or otherwise destroyed, they show up in stunning detail in satellite photos. By analyzing such images, “in an area of about 2500 square kilometers, we’ve located 158 major settlements, 184 cemeteries, 30 square kilometers of fields, plus a variety of irrigation systems,” Mattingly says. Not only have he and his team been able to select the most promising sites for on-the-ground fieldwork, but they can also use the images to reconstruct the Garamantes’ regional footrpint—something that would have been very hard to do by excavating one site at a time.

Satellite images are less helpful when it comes to the Amazon rainforest, where a thick canopy of vegetation blocks the view of most signs of ancient settlement. So José Iriarte, an archaeologist at the University of Exeter in the United Kingdom, has opted for drones to search for the region’s lost civilizations.

When ecologists look at the Amazon, they see “virgin wilderness” untouched by humans, Iriarte says. But thanks to the discovery of large-scale earthworks called geogylphs and terra preta—“black earth” that was purposely enriched by humans in the past—archaeologists have concluded that at least parts of the rainforest must have been home to large, agricultural settlements. “Now it’s time to start quantifying past human impact in different parts of the Amazon,” Iriarte says.

Iriarte’s drone will be outfitted with LiDAR equipment to map the ground through the trees, which is very helpful for revealing large geoglyphs that may be hidden beneath the canopy. But the unmanned aerial vehicle will also be equipped with tools that can analyze the distribution of the plants themselves. If past cultures “farmed” the rainforest by cultivating helpful crops in specific places, their practices may have shaped which species grow where, even today—which could change the way we think about conservation in the Amazon. “The very biodiversity that we seek to safeguard may itself be a legacy of centuries or millennia of human intervention,” Iriarte says.

“These new technologies have just opened up these regions to us,” Mattingly says. But time is of the essence. Sites in both the Amazon and the Sahara are being built over by modern development, sometimes by people who don’t understand the archaeological importance of what they are destroying. Remote sensing data may be the only way to capture information about these sites before they are gone for good.

Check out our full coverage of the AAAS annual meeting.

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