GIFT FROM THE PAST
“Landscape,” in this case, is meant exactly—Amazonian Indians literally created the ground beneath their feet. According to Susanna Hecht, a geographer at the University of California at Los Angeles, researchers into upland Amazonia took most of their soil samples along the region’s highways, which indeed passed through areas with awful soil—some regions were so saturated with toxic aluminum that they are now being mined for bauxite. A few scientists, though, found patches of something better. “In part because of the empty-Amazon model,” Hecht told me, these were “seen as anomalous and insignificant.” But in the 1990s researchers began studying these unusual regions of terra preta do Índio—rich, fertile “Indian dark earth” that anthropologists believe was made by human beings.
Throughout Amazonia, farmers prize terra preta for its great productivity; some have worked it for years with minimal fertilization. Among them are the owners of the papaya orchard I visited, who have happily grown crops on their terra preta for two decades. More surprising still, the ceramics in the farm’s terra preta indicate that the soil has retained its nutrients for as much as a millennium. On a local level, terra preta is valuable enough for locals to dig it up and sell as potting soil, an activity that, alas, has already destroyed countless artifacts. To the consternation of archaeologists, long planters full of ancient terra preta, complete with pre-Columbian potsherds, greet visitors to the Santarém airport. Because terra preta is subject to the same punishing conditions as the surrounding bad soils, “its existence is very surprising,” according to Bruno Glaser, a chemist at the Institute of Soil Science and Soil Geography at the University of Bayreuth, Germany. “If you read the textbooks, it shouldn’t be there.” *25
Because careful surveys of Amazon soils have never been taken, nobody knows the amount and distribution of terra preta. Woods has guessed that terra preta might represent as much as 10 percent of the Amazon basin, an area the size of France. A recent, much more conservative estimate is that it covers .1 to .3 percent of the basin, a few thousand square miles. The big difference between these numbers matters less than one might expect: a few thousand square miles of farmland was enough to feed the millions in the Maya heartland.
Most big terra preta sites are on low bluffs at the edge of the floodplain. Typically, they cover five to fifteen acres, but some encompass seven hundred or more. The layer of black soil is generally one to two feet deep but can reach more than six feet. According to a recent study led by Dirse Kern, of the Museu Goeldi in Belém, terra preta is “not associated with a particular parent soil type or environmental condition,” suggesting that it was not produced by natural processes. Another clue to its human origin is the broken ceramics with which it is usually mixed. “They practiced agriculture here for centuries,” Glaser told me. “But instead of destroying the soil, they improved it, and that is something we don’t know how to do today” in tropical soils.
As a rule, terra preta has more “plant-available” phosphorus, calcium, sulfur, and nitrogen than is common in the rain forest; it also has much more organic matter, better retains moisture and nutrients, and is not rapidly exhausted by agricultural use when managed well. The key to terra preta’s long-term fertility, Glaser says, is charcoal: terra preta contains up to sixty-four times more of it than surrounding red earth. Organic matter “sticks” to charcoal, rather than being washed away or attaching to other, nonavailable compounds. “Over time, it partly oxidizes, which keeps providing sites for nutrients to bind to.” But simply mixing charcoal into the ground is not enough to create terra preta. Because charcoal contains few nutrients, Glaser argued, “high-nutrient inputs—excrement and waste such as turtle, fish, and animal bones—are necessary.” Special soil microorganisms are also likely to play a role in its persistent fertility, in the view of Janice Thies, a soil ecologist who is part of a Cornell University team studying terra preta. “There are indications that microbial biomass is higher in terra preta than in other forest soils,” she told me, which raises the possibility that scientists might be able to create a “package” of charcoal, nutrients, and microfauna that could be used to transform bad tropical soil into terra preta.
Despite the charcoal, terra preta is not a by-product of slash-and-burn agriculture. To begin with, slash-and-burn simply does not produce enough charcoal to make terra preta—the carbon mostly goes into the air in the form of carbon dioxide. Instead, Indians apparently made terra preta by a process that Christoph Steiner, a University of Bayreuth soil scientist, has dubbed “slash-and-char.” Instead of completely burning organic matter to ash, ancient farmers burned it incompletely to make charcoal, then stirred the charcoal into the soil. In addition to its benefits to the soil, slash-and-char releases much less carbon into the air than slash-and-burn, which has large potential implications for climate change. Trees store vast amounts of carbon in their trunks, branches, and leaves. When they die or people cut them down, the carbon is usually released into the atmosphere, driving global warming. Experiments by Makoto Ogawa of the Kansai Environmental Engineering Center, near Kyoto, Japan, demonstrated that charcoal retains its carbon in the soil for up to fifty thousand years. “Slash-and-char is very clever,” Ogawa told me. “Nobody in Europe or Asia that I know of ever understood the properties of charcoal in soil.”
Indians are still making terra preta in this way, according to Hecht, the UCLA geographer. Hecht spent years with the Kayapó, in central Amazonia, watching them create “low-biomass” fires “cool enough to walk through” of pulled-up weeds, cooking waste, crop debris, palm fronds, and termite mounds. Burning, she wrote, is constant: “To live among the Kayapó is to live in a place where parts of the landscape smolder.” Hecht regards Indian fire as an essential part of the Amazonian landscape, as it was in the forests of eastern North America. “We’ve got to get over this whole Bambi syndrome,” she told me, referring to the movie’s forest-fire scene, which has taught generations of children that burning wildlands is evil. “Let the Kayapó burn the rainforest—they know what they’re doing.”
In a preliminary test run at creating terra preta, Steiner, Wenceslau Teixeira of the Brazilian Agricultural Research Enterprise, and Wolfang Zech of the University of Bayreuth applied a variety of treatments involving charcoal and fertilizers for three years to rice and sorghum plots outside Manaus. In the first year, there was little difference among the treatments (except for the control plots, in which almost nothing grew). By the second year, Steiner said, “the charcoal was really making a difference.” Plots with charcoal alone grew little, but those treated with a combination of charcoal and fertilizer yielded as much as 880 percent more than plots with fertilizer alone. His “terra preta” was this productive, Steiner told me, despite making no attempt to re-create the ancient microbial balance.
Beginning a little more than two thousand years ago, the central and lower Amazon were rocked by extreme cultural change. Arawak-speaking groups migrated in from the south and west, sometimes apparently driving Tupí-speaking groups north and east. Sedentary villages appeared. And so did terra preta. No one yet knows if or how these events were related. By about the time of Christ the central Amazon had at least some large, settled villages—Neves, Petersen, and Bartone excavated one on a high bank about thirty miles up the Río Negro. Judging by carbon dating and the sequence of ceramics, they believe the site was inhabited in two waves, from about 360 B.C., when terra preta formation began, to as late as 1440 A.D. “We haven’t finished working, but there seems to be a central plaza and some defensive ditches there,” Petersen told me. The plaza was at least a quarter mile long; the ditch, more than three hundred feet long and up to eighteen feet wide and six feet deep: “a big, permanent settlement.”
Terra preta showed up at the papaya plantation between 620 and 720 A.D. By that time it seems to have been underneath villages throughout the central Amazon. Several hundred years later it reached the upper Xingú, a long Amazon tributary with its headwaters deep in southern Brazil. People had lived around the Xingú for a long time, but around 1100 or 1200 A.D., Arawak-speaking people appear to have moved in, jostling shoulders with people who spoke a Tupí-Guaraní language. In 2003 Heckenberger, who had worked with Petersen and Neves, announced in Science that in this area he and his colleagues had turned up remains of nineteen large villages linked by a network of wide roads “in a remarkably elaborate regional plan.” Around these settlements, which were in place between approximately 1250 and 1400 A.D., the Xinguanos built “bridges, artificial river obstructions and ponds, raised causeways, canals, and other structures…a highly elaborate built environment, rivaling that of many contemporary complex societies of the Americas and elsewhere.” The earlier inhabitants left no trace of terra preta; the new villages quickly set down thick deposits of black earth. “To me,” Woods said, “it looks as if someone invented it, and the technique spread to the neighbors.”
Because Amazonia lacks stone and metal and its hot, wet climate rapidly destroys wood and cloth, material traces of past societies are hard to find. The main exception is pottery, striking examples of which survive, such as the highly decorative vessels from the Santarém area (right, this one probably made in the seventeenth century). Stone, being rare, was reserved for special items such as the pestles (left) used to grind the hallucinogenic snuff yobo.
One of the biggest patches of terra preta is on the high bluffs at the mouth of the Tapajós, near Santarém. First mapped in the 1960s by the late Wim Sombroek, director of the International Soil Reference and Information Center in Wageningen, the Netherlands, the terra preta zone is three miles long and half a mile wide, suggesting widespread human habitation—exactly what Orellana saw. The plateau has never been carefully excavated, but observations by geographers Woods and Joseph McCann of the New School in New York City indicate that it is thick with ceramics. If the agriculture practiced in the lower Tapajós were as intensive as in the most complex cultures in precontact North America, Woods told me, “you’d be talking something capable of supporting about 200,000 to 400,000 people”—making it at the time one of the most densely populated places in the world.
Woods was part of an international consortium of scientists studying terra preta. If its secrets could be unraveled, he said, it might improve the expanses of bad soil that cripple agriculture in Africa—a final gift from the peoples who brought us tomatoes, maize, manioc, and a thousand different ways of being human.
“Betty Meggers would just die if she heard me saying this,” Woods told me. “Deep down her fear is that this data will be misused.” In 2001, Meggers charged in an article in Latin American Antiquity that archaeologists’ claims that the Amazon could support intensive agriculture were effectively telling “developers [that they] are entitled to operate without restraint.” These researchers had thus become unwitting “accomplices in the accelerating pace of environmental degradation.” Centuries after the conquistadors, she lamented, “the myth of El Dorado is being revived by archaeologists.”
Doubtless her political anxieties are not without justification, although—as some of her sparring partners observed—it is difficult to imagine greedy plutocrats “perusing the pages of Latin American Antiquity before deciding to rev up the chainsaws.” But the new picture doesn’t automatically legitimate burning down the forest. Instead it suggests that for a long time clever people who knew tricks that we have yet to learn used big chunks of Amazonia nondestructively. Faced with an ecological problem, the Indians fixed it. Rather than adapt to Nature, they created it. They were in the midst of terra-forming the Amazon when Columbus showed up and ruined everything.