Gonzalo's quest descended rapidly from the quixotic to the calamitous. Having no idea where to find El Dorado, he blundered randomly for months about the eastern foothills of the Andes, then as now a country of deep forest. Because the mountains catch all the moisture from the Amazon winds, the terrain is as wet as it is steep. It is also pullulatingly alive: howling with insects, hot and humid as demon's breath, perpetually shaded by mats of lianas and branches. Within weeks most of the horses died, their hooves rotting in the mire. So did most of the Indian laborers, felled by being worked to exhaustion in a hot, humid land twelve thousand feet below their cool mountain home. Having lost their beasts of burden, animal and human, the conquistadors painfully cobbled together a crude boat and floated their guns and heavy equipment down the Napo River, an upper tributary of the Amazon. Meanwhile, the soldiers slogged along the banks, a parallel but more laborious course.

The forest grew yet thicker, the countryside less inhabited. Soon they were utterly alone. "Not a bark dimpled the waters," William H. Prescott wrote in his History of the Conquest of Peru. "No living thing was to be seen but the wild tenants of the wilderness, the unwieldy boa, and the loathsome alligator basking on the borders of the stream." With no Indian villages to rob for supplies, the expedition ran short of food. The forest around them had plenty of food, but the Spaniards didn't know which plants were edible. Instead they ate all the surviving pigs, then the dogs, and then turned to spearing lizards. More and more men were sick. Having previously heard vague tales of a wealthy country further down the Napo, Francisco de Orellana, Gonzalo Pizarro's second-in-command and cousin, suggested that he split off part of the expedition to see if he could obtain supplies. Pizarro agreed, and Orellana set off in the expedition's prized boat on December 26, 1541, with a crew of fifty-nine, Carvajal among them.

Nine days and six hundred miles down the Napo, Orellana found villages with food-a society he called Omagua. His men gorged themselves and then considered their options. They did not relish the prospect of ferrying supplies back up the river to Gonzalo Pizarro and the rest of the expedition; rowing against the current would be difficult, and, as they knew all too well, there was nothing to eat along the way. Orellana decided instead to leave the starving Gonzalo to his fate and take the boat to the mouth of the river, which he correctly believed emptied into the Atlantic (incorrectly, he believed that the river was not too long).

Knowing that Gonzalo, in the unlikely event that he survived, would regard Orellana's actions as treasonous, Carvajal took upon himself the task of creating a justificatory paper trail: an account "proving" that the choice to abandon Gonzalo had been forced on them. To satisfy Spanish legal requirements, Orellana made a show of resigning his temporary command rather than leave Gonzalo. The crewmen, Carvajal claimed, then swore "by God...by the sign of the Cross, [and] by the four sacred Gospels" that they wanted Orellana to return as leader. Bowing to pressure, Orellana accepted the post. Then they built a second vessel and set off downstream.

Their worries about Gonzalo's reaction were well-founded. Half a year after Orellana's departure, the surviving members of his expedition staggered in rags into Quito. Gonzalo was among them. He wasted no time in demanding Orellana's arrest and execution. In taking the boat, most of the canoes, and some of the weapons from his famished troops, Orellana had displayed, Gonzalo said, "the greatest cruelty that ever faithless men have shown."

Meanwhile, Orellana and his men had spent five months floating down the Amazon, Carvajal recording every moment. It is inconceivable that their surroundings did not induce awe. Vastly bigger than any river in Europe or Asia, the Amazon contains a fifth of the earth's above-ground fresh water. It has islands the size of countries and masses of floating vegetation the size of islands. Half a dozen of its tributaries would be world-famous rivers anywhere else. A thousand miles up from the Atlantic, the river is still so broad that at high water the other side is only a faint dark line on the horizon. Ferries take half an hour to make the crossing. Seagoing vessels travel all the way up to Iquitos, Peru, 2,300 miles from the river's mouth, the furthest inland deep-ocean port in the world.

The conventional view of Amazonia: endless untouched forest. The forest indeed exists, but humankind has long been one of its essential components.

The prospect of a mutiny trial constantly in mind, Carvajal wrote relatively little about his extraordinary surroundings. Instead he focused on creating a case for the value and necessity of Orellana's journey. To the contemporary eye, he didn't have much to work with. His case had three main elements: (1) the forcing of Orellana's hand (see above); (2) the crew's devotion to the Holy Virgin; and (3) the degree to which they suffered en route. In truth, the last does not seem feigned. In Carvajal's account, pain and sickness alternate with starvation. "We were eating leather from the seats and bows of saddles," runs one all-too-typical reminiscence. "Not to mention the soles and even whole shoes [with] no sauce other than hunger itself."

Encounters with the river's inhabitants were frequent and often hostile. Passing the native domains strung along the river was like passing a line of angry hives. Forewarned of the visitors' arrival by drum and messenger, Indians awaited them behind trees and in concealed canoes, shot fusillades of poisoned arrows, then withdrew. A few miles downriver would be the next group of Indians, and the next attack. Except when demanding food, the expedition navigated as far as possible from every village. Nonetheless three Spaniards died in battle. An arrow hit Carvajal in the face, blinding him in one eye.

Carvajal wrote little about the peoples who spent so much time trying to kill him. But the small amount he did write depicts a crowded and prosperous land. Approaching what is now the Peru-Brazil border, he noted that "the farther we went the more thickly populated and the better did we find the land." One 180-mile stretch was "all inhabited, for there was not from village to village a crossbow shot." The next Indians down the river had "numerous and very large settlements and very pretty country and very fruitful land." And just beyond them were villages crowded cheek by jowl-"there was one day when we passed more than twenty." In another place Carvajal saw a settlement "that stretched for five leagues without there intervening any space from house to house."

Near the mouth of the Tapajos, about four hundred miles from the sea, Orellana's ragtag force came across the biggest Indian settlement yet-its homes and gardens lined the riverbank for more than a hundred miles. "Inland from the river, at a distance of one or two leagues...there could be seen some very large cities." A floating reception force of more than four thousand Indians-two hundred war canoes, each carrying twenty or thirty people-greeted the Spanish. Hundreds or thousands more stood atop the bluffs on the south bank, waving palm leaves in synchrony to create a kind of football wave that Carvajal clearly found peculiar and unnerving. His attention riveted to the scene, he for once noted some details. Approaching in their great canoes, the Indian soldiers wore brilliant feather cloaks. Behind the canoe armada was a floating orchestra of horns, pipes, and rebecs like three-stringed lutes. When the music played, the Indians attacked. Only the tremendous surprise created by the Spaniards' firearms provided the opportunity to escape.

Orellana died in 1546 on a second, failed voyage to the Amazon. Carvajal went on to achieve modest renown as a priest in Lima, dying peacefully at the age of eighty. Neither Orellana's journey nor Carvajal's account of it received the attention they merited; indeed, Carvajal's work was not formally published until 1894. Part of the reason for the lack of attention is that Orellana didn't conquer anything-he simply managed to emerge with his life. But another part is that few people believed Carvajal's description of the Amazon.

The main cause for skepticism was his notorious claim that halfway down the river the Spaniards were attacked by tall, topless women who fought without quarter and lived without men. When these "Amazons" wanted to reproduce, Carvajal explained, they captured males. After the women's "caprice [had] been suited," they returned the spent abductees to their homes. Any bravo who saw the prospect of some caprice-suiting as inviting enough to visit the Amazons himself, Carvajal solemnly warned, "would go a boy and return an old man." This absurd story was viewed as proof of Carvajal's untrustworthiness and Orellana's faithlessness. "Mentirosa [full of lies]," historian Francisco Lopez de Gomara scoffed soon after Carvajal finished his manuscript.

Physical scientists were especially unwilling to accept his depiction of the Amazon. To ecologists, the great tropical forest in South America was and is the planet's greatest wilderness, primeval and ancient, an Edenic zone touched by humankind lightly if at all. Constrained by its punishing climate, poor soil, and lack of protein, these scientists argue, large-scale societies have never existed-can never exist-in the river basin. Amazonia thus could not have been the jostling, crowded place described by Carvajal.

As anthropologists have learned more about the vagaries of fieldwork, they have treated Carvajal more kindly. "He may not have been making up the Amazons out of whole cloth," William Balee, the Tulane anthropologist, told me. "It is possible that he saw female warriors, or warriors whom he believed were female. If he asked Indians about them, he could have misunderstood their answers. Or he could have understood them correctly, but not understood that his informants were pulling his leg. We now understand that ethnography is complex, and it's easy to go wrong." In recent years, these blanket dismissals have been challenged.

More important, anthropologists, archaeologists, geographers, and historians who were reassessing the environmental impact of indigenous cultures in North and Central America inevitably turned to the tropical forest. And in growing numbers researchers came to believe that the Amazon basin, too, bears the fingerprints of its original inhabitants. Far from being the timeless, million-year-old wilderness portrayed on calendars, these scientists say, today's forest is the product of a historical interaction between the environment and human beings-human beings in the form of the populous, long-lasting Indian societies described by Carvajal.

Such claims raise the hackles of many conservationists and ecologists. Amazonia, activists warn, is sliding toward catastrophe so rapidly that saving it must become a global priority. With bulldozers poised to destroy one of the planet's last great wild places, environmentalists say, claiming that the basin comfortably housed large numbers of people for millennia is so irresponsible as to be almost immoral-it is tantamount to giving developers a green light.

The Amazon is not wild, archaeologists and anthropologists retort. And claiming that it is will, in its ignorance, worsen the ecological ailments that activists would like to cure. Like their confreres elsewhere in the Americas, Indian societies had built up a remarkable body of knowledge about how to manage and improve their environment. By denying the very possibility of such practices, these researchers say, environmentalists may hasten, rather than halt, the demise of the forest.

GREEN PRISON.

The nineteenth-century naturalist Thomas Belt may have said it best. In what Darwin called "the best of all natural history journals," Belt set down what has become the classic image of the tropical forest: a gigantic, teeming expanse, wildly diverse biologically but otherwise undifferentiated. "A ceaseless round of ever-active life weaves the forest scenery of the tropics into one monotonous whole," as he put it. And since Belt's day, terms like "Amazonia" and "Amazon basin" are often used as if they referred to a single, homogeneous entity.

AMAZON BASIN.

This practice irritates professional geographers no end. Strictly speaking, "Amazon basin" refers to the drainage of the Amazon and its tributaries. "Amazonia," by contrast, refers to the bigger region bounded by the Andes to the west, the Guiana Shield to the north, and the Brazilian Shield to the south. And neither is coterminous with the "Amazonian rainforest." To begin with, not all of the "Amazonian rainforest" is rainy-parts of it receive little more precipitation per year than New York City. On top of that, about a third of Amazonia is not forest but savanna-the Beni, in Bolivia, is the biggest chunk. The river's floodplain and that of its tributaries take up another 5 to 10 percent of the basin. Only about half of Amazonia is upland forest-vines overhead in a tangle like sailing ships rigged by drunks; tree branches in multiple layers; beetles the size of butterflies and butterflies the size of birds-the ecosystem that people outside the region usually mean when they say "Amazon."

To biologists, the apparent fertility of the upland forest is a sham. This thesis was laid out clearly in Paul Richards's classic 1952 study, The Tropical Rain Forest. To be sure, Richards said, the Amazon forest is uniquely diverse and beautiful. But its exuberant canopy is a mask covering an impoverished base. The base is the region's poor soil. No matter what its original condition, the intense rain and heat of the forest have eroded its surface, washed out all its minerals, and decomposed vital organic compounds. As a result, much of the red Amazonian soil is weathered, harshly acid, and almost bereft of essential nutrients-one reason ecologists refer to the tropical forest as a "wet desert."

Correspondingly, most nutrients in tropical forests are stored not in the soil, as in temperate regions, but in the vegetation that covers it. When leaves or branches fall, the carbon and nitrogen in the debris are rapidly reabsorbed by the hyperefficient root systems of tropical plants. If loggers or farmers clear away the vegetation, they also remove the local supply of nutrients. Normally the forest quickly fills in bare spots, such as those created when big trees fall, and damage is kept to a minimum. But if the opening is too large or the ground is kept clear too long, the sun and rain decompose whatever organic matter remains and bake the surface into something resembling brick in both color and impermeability. In short order, the land becomes almost incapable of sustaining life. Thus the tropical forest, despite its fabulous vitality, exists on a knife edge.

These views were picked up and amplified in Amazonia: Man and Culture in a Counterfeit Paradise, by Betty J. Meggers, the Smithsonian archaeologist. Published in 1971, it may be the most influential book ever written about the Amazon. Agriculture, Meggers pointed out, depends on extracting the wealth of the soil. With little soil wealth to extract, she said, Amazonian farmers face inherent ecological limitations. The only form of agriculture they can practice for a long time is "slash-and-burn," or "swidden," as it is sometimes known. Farmers clear small fields with axes and machetes, burn off the chaff and refuse, and plant their seeds. The ash gives the soil a quick shot of nutrients, giving the crop a chance. As the crops grow, the jungle rapidly returns-weeds first, then fast-growing tropical trees. In the few years before forest recovers the plot, farmers can eke something out of the land.

Slash-and-burn, Meggers told me, is "a superb response to ecological limits." Farmers grab a few harvests, but the soil is not bared to rain and sun long enough to incur permanent damage. Switching from field to field to field, swidden farmers live in the forest without destroying the ecosystems they depend on: a supple, balanced harmony. This ancient lifeway survives today, according to this theory, in the ring-shaped compounds of the Yanomamo. (Most of the Yanomamo actually live around South America's other huge river system, the Orinoco, but they are seen as emblematic of Amazonia as well.) Gliding nearly nude beneath the trees, cultivating their temporary gardens, the Yanomamo are often said to be windows into the past, living much the same lives as their great-great-great-grandparents. Their long-term existence has not damaged the forest, Meggers told me, a testament to slash-and-burn's power to keep human groups sustainably within the rigid ecological limits of the tropics.

A second reason that slash-and-burn is required, Meggers told me, is the region's propensity for suffering "mega-Nino events"-superstrong El Nino climate swings that occur every three hundred to five hundred years. In the archaeological record, she said, "We're able to pick up severe droughts related to these mega-Nino events. What these did was reduce the food supply. The 1998 El Nino was a small example-they saw droughts, forest fires, and reduction of resources from when trees don't flower." Forest fires in the northern state of Roraima that year claimed such a huge area that Brazil requested aid from the United Nations. In the past, Meggers said, "the well-established groups that were sitting in one territory for several hundred years couldn't survive [the droughts], so they broke up. We see this repeated at least four times in the last two millennia." In other words, any Indians who tried to go beyond slash-and-burn to permanent cultivation would be knocked back to slash-and-burn by a mega-Nino. Slash-and-burn, she said, "avoids the risks, including the risk of growth-it's the smart thing to do."

Ethnographic celebrities, the Yanomamo are often portrayed as windows into the past, inhabitants of a forest wilderness they have inhabited, almost unchanged, for millennia. Recent studies have cast doubt on this picture. Indeed, the Yanomamo are relative newcomers to their homeland, many of them moving there only in the seventeenth century as they fled European diseases and cruelty further south. Some scholars believe their societies were originally so much larger and more materially complex that what is often pictured as an almost idyllic, "natural" existence is in fact a life in poor exile.

Swidden, Meggers admitted, has a major drawback: it cannot yield enough to support a complex society. More intensive farming might produce the requisite surplus, but cannot be sustained; the plowed land, exposed to the elements, is destroyed in as little as a decade. Even with slash-and-burn, ecologists say, the forest can take as much as a hundred years to return completely to its previous state. European-style agriculture would not only fall victim to mega-Ninos, it would permanently ruin the forest soils.

Carvajal therefore misunderstood what he saw, Meggers told me. Or else he had simply made up everything, and not just the Amazons. Caught in a lush, green trap, Indian villages could not possibly have grown as large as he reported-indeed, Meggers once proposed an upper limit of a thousand on their population. And the villages could not have been the sophisticated places he described, with their chiefly rulers, social classes, and specialized laborers (those military musicians on the Tapajos, for example). That was why archaeologists and anthropologists had come across the ruins of complex societies throughout Mesoamerica and the Andes, but saw only hunter-gatherers and slash-and-burners in Amazonia.

"The basic thing about the Amazon is that these people had a long-term period to learn about and experience and benefit from their knowledge of the environment," Meggers said. "Any group that over-exploited their environment was going to be dead. The ones that survived, the knowledge got built into their ideology and behavior with taboos and other kinds of things." Having reached the optimal cultural level for their environment, she explained, Amazon Indian lives changed little, if at all, for at least two thousand years.

As proof, Meggers pointed to Marajo, an island more than twice the size of New Jersey that sits like a gigantic stopper in the mouth of the Amazon. The island, low and often swampy, is created by the collision of the Amazon with the sea, which forces the river to disgorge dissolved sediments. Much of the island is submerged during the rainy season, and even in the dry summer pieces of the mazy shoreline are constantly calving off like icebergs and falling into the water. Yet despite the unpromising setting, the Marajoara created a sophisticated society there from about 800 to 1400 A.D.

The island's pottery, some of it very large, has long been celebrated for its painted and incised representations of animals and plants, which are ornately entangled in a profusion that recalls the forest itself. The skillful pottery indicated that Marajo was a large-scale society-the only one then known in all of Amazonia. In the late 1940s Meggers and her husband, archaeologist Clifford J. Evans, decided to learn more.

The decision was ambitious. Archaeologists have traditionally avoided tropical forests, because the climate destroys all wood, cloth, and organic material-except for ceramics and stone, there is little left to dig up. And the Amazon basin, essentially an astoundingly large river valley made of deposited mud, has almost no stone, so archaeologists wouldn't even find that. (Because the nearest deposits of metal ore were in the Andes, thousands of miles upstream, Amazonian peoples had no metal.) At Marajo, Meggers and Evans soon noticed an oddity: the earliest traces of Marajoara culture were the most elaborate. As the centuries advanced, the quality of the ceramics inexorably declined. The designs became cruder, the repertoire of themes reduced, the technical skill diminished. At the beginning, some grave sites were more elaborate than others, a testament to social stratification. Later on, all the dead were treated in the same mundane way. Early in their history, the Marajoara must have sneered at the lowly cultures on their borders. But as the forest, in a process out of Heart of Darkness, stripped away the layers of civilization, they became indistinguishable from their neighbors. A hundred years before Columbus, Meggers told me, they were blasted by a mega-Nino and then overrun by one of their erstwhile inferiors. The history of Marajo was all fall and no rise.

Betty Meggers.

In a boldly written article in American Anthropologist in 1954, Meggers proclaimed the implications: There is a force at work to which man through his culture must bow. This determinant operates uniformly regardless of time, place (within the forest), psychology or race. Its leveling effect appears to be inescapable. Even modern efforts to implant civilization in the South American tropical forest have met with defeat, or survive only with constant assistance from the outside. In short, the environmental potential of the tropical forest is sufficient to allow the evolution of culture to proceed only to the level represented by [slash-and-burn farmers]; further indigenous evolution is impossible, and any more highly evolved culture attempting to settle and maintain itself in the tropical forest environment will inevitably decline to the [slash-and-burn] level.

The impossibility of passing beyond slash-and-burn, Meggers said, was a consequence of a more general "law of environmental limitation of culture." And she stated the law, italicizing its importance: "The level to which a culture can develop is dependent upon the agricultural potentiality of the environment it occupies."

How did Marajo escape, even temporarily, the iron grasp of its environment? And why was there no sign of its initial climb past ecological limits, only of its subsequent collapse before them? Meggers and Evans provided the answers three years later in an influential monograph. Marajo, they said, was not actually an Amazonian society. In fact, it was a failed cutting from a more sophisticated culture in the Andes, a cousin of Wari or Tiwanaku. Stranded in the wet desert of the Amazon, the culture struggled to gain its footing, tottered a few steps, and died.

Counterfeit Paradise was the product of more than twenty years of research. But that was not the sole reason for the book's influence. Meggers's message of limitation, published within a year of the first Earth Day, resonated in the ears of readers newly converted to the ecological movement. Since then countless campaigns to save the rainforest have driven home its lesson: development in tropical forests destroys both forests and their developers. Promulgated in ecology textbooks, Meggers's argument became a wellspring of the campaign to save rainforests, one of the few times in recent history that humankind has actually tried to profit from the lessons of the past.

Yet even as the themes of Counterfeit Paradise spread to the worlds of natural science and political activism, Meggers's ideas exerted ever-diminishing influence in archaeology itself. From her distinguished post at the Smithsonian, she battled on behalf of the law of environmental limitation. But her main accomplishment may have been inadvertently to keep new ideas about Amazonian history from the public eye-ideas about its past that may, according to their advocates, play a role in safeguarding its future.

PAINTED ROCK CAVE.

"Rather than admiration or enthusiasm," the great Brazilian writer Euclides da Cunha wrote at the end of the nineteenth century, "the feeling that overtakes one when first encountering the Amazon is foremost one of disappointment." Like today's ecotourism brochures, the accounts of the great river basin in da Cunha's time celebrated its immensity but rarely dwelled on its extreme flatness-in the Amazon's first 2,900 miles the vertical drop is only 500 feet. "It is as though the place lacks vertical lines," da Cunha complained. "In a few hours the observer gives in to the fatigue of the unnatural monotony." Every year the river floods-not a disaster, but a season. A channel that is one mile wide in the dry season can become thirty miles wide in the wet. After five months the water recedes, leaving behind a layer of rich sediment. From the air, the river seems to ooze like dirty metal through a wash of green utterly devoid of the romantic crags, arroyos, and heights that signify wildness and natural spectacle to most people of European descent.

The area around the lower-Amazon city of Santarem is an exception. West of town, the Tapajos pours into the Amazon from the south, creating an inland bay that at high water is fifteen miles wide and a hundred miles long. The flood rises high enough to cover low river islands in knee-deep water, leaving their trees to stand out like miracles in mid-channel. Fishers from town ride their bicycles into little boats, parking the bikes while working by hanging them in the offshore trees. The bay is lined with bluffs high enough to cast long shadows. Almost five hundred years ago, Indians lined the edge of the rise, taunting Orellana by waving palm fronds.

On the opposite, northern side of the river are a series of sandstone ridges that reach down from the Guiana Shield in the north, halting close to the water's edge. Five hundred feet high and more, they rise above the canopy like old tombstones. Many of the caves in the buttes are splattered with ancient pictographs-rock paintings of hands, stars, frogs, and human figures, all reminiscent of Joan Miro, in overlapping red and yellow and brown. In the 1990s one of these caves, Caverna da Pedra Pintada-Painted Rock Cave-drew considerable attention in archaeological circles.

Wide and shallow and well lighted, Painted Rock Cave is less thronged with bats than some of the other caves. The arched entrance is twenty feet high and electric with gaudy imagery. Out front is a sunny natural patio, suitable for picnicking, that is edged by a few big rocks. During my visit I ate a sandwich atop a particularly inviting stone and looked through a stand of peach palms over the treetops to the water seven miles away. The people who created the petroglyphs, I thought, must have done about the same thing.

Painted Rock Cave has attracted scientists since the mid-nineteenth century, when Alfred Russel Wallace visited it. Wallace, a naturalist, was more interested in the palm trees outside the caves than the people who had lived inside them. The latter were left to an archaeologist, Anna C. Roosevelt, then at the Field Museum. To her exasperation, press accounts of Roosevelt's work often stress her descent from Theodore Roosevelt (she is his great-granddaughter), as if her lineage were more noteworthy than her accomplishments. In truth, though, she has demonstrated something of her ancestor's flare for drama and controversy.

Roosevelt first came to public attention when she reexcavated Marajo in the 1980s. By using a battery of new remote-sensing techniques-including total-station topographic mapping, ground-penetrating radar, and scanning for slight variations in magnetic field strength, electrical conductivity, and electrical resistance-she was able to build up a picture of Marajo far more detailed than Meggers and Evans could have in the 1940s and 1950s, when they worked there. Detailed-and different.

Published in 1991, Roosevelt's initial report on Marajo was like the antimatter version of Counterfeit Paradise. A few scientists had challenged Meggers's ideas; Roosevelt excoriated them from top to bottom. Far from being a failed offshoot of another, higher culture, she concluded, Marajo was "one of the outstanding indigenous cultural achievements of the New World," a powerhouse that lasted for more than a thousand years, had "possibly well over 100,000" inhabitants, and covered thousands of square miles. Rather than damaging the forest, Marajo's "large population, highly intensive subsistence, [and] major systems of public works" had improved it: the places formerly occupied by the Marajoara showed the most luxuriant and diverse growth. "If you listened to Meggers's theory, these places should have been ruined," Roosevelt told me.

Rather than pressing down on Marajo, she said, the river and forest opened up possibilities. In highland Mexico, "it wasn't easy to get away from other people. With all those rocky hillsides and deserts, you couldn't readily start over. But in the Amazon, you could run away-strike off in your canoe and be gone."

As in Huckleberry Finn? I asked.

In this reconstruction based on archaeologist Anna Roosevelt's view of Marajoara society, houses cluster on artificial platforms above the wet ground while farm fields stretch into the island's interior.

"If you like," she said. "You could go [along the river] where you wanted and homestead-the forest gives you all kinds of fruit and animals, the river gives you fish and plants. That was very important to societies like Marajo. They had to be much less coercive, much more hang-loose, much more socially fluid, or people wouldn't stay there." Compared with much of the rest of the world at that time, people in the Amazon "were freer, they were healthier, they were living in a really wonderful civilization."

Marajo never had the grand public monuments of a Tenochtitlan or a Qosqo, Roosevelt noted, because its leaders "couldn't compel the labor." Nonetheless, she said, Marajo society was "just as orderly and beautiful and complex. The eye-opener was that you didn't need a huge apparatus of state control to have all that. And this had been entirely missed by Meggers, who couldn't see past her environmental-determinist theories. And I said so much in my book."

Meggers reacted to Roosevelt's critiques by sneering at her "polemical tone" and "extravagant claims." In concluding that large areas of Marajo had been continuously inhabited, Roosevelt had (according to Meggers) committed the beginner's error of confusing a site that had been occupied many times by small, unstable groups for a single, long-lasting society. Cultural remains, Meggers explained to me, "build up on areas of half a kilometer or so, because [shifting Indian groups] don't land exactly on the same spot. The decorated types of pottery don't change much over time, so you can pick up a bunch of chips and say, 'Oh, look, it was all one big site!' Unless you know what you're doing, of course." From her point of view, claiming that Amazonian societies could escape their environmental constraints was little more than a display of scientific ignorance, the archaeological version of trying to design perpetual-motion machines.

Anna Roosevelt.

To Meggers's critics, the ecological-limits argument was not only wrong, but familiar-and familiar in an uncomfortable way. From the first days of contact, Europeans have perceived the Indians of the tropics as living in timeless stasis. Michel de Montaigne admiringly claimed in 1580 that the inhabitants of the Amazon had "no knowledge of numbers, no terms for governor or political superior, no practice of subordination or of riches or poverty...no clothing, no agriculture, no metals." They abided, he said, "without toil or travail" in a "bounteous" forest that "furnishes them abundantly with all they need.... They are still in that blessed state of desiring nothing beyond what is ordained by their natural necessities: for them anything further is merely superfluous."

Montaigne's successors quickly turned his views upside-down. Like him, they viewed Amazonians as existing outside history, but they now regarded this as a bad thing. The French natural historian Charles Marie de la Condamine retraced Orellana's journey in 1743. He emerged with great regard for the forest-and none for its inhabitants. The peoples of the Peruvian Amazon were nothing more than "forest animals," he said. "Before making them Christians, they must first be made human." In softened form, Condamine's views persisted into the twentieth century. "Where man has remained in the tropics, with few exceptions, he has suffered arrested development," the prominent geographer Ellen Churchill Semple remarked in 1911. "His nursery has kept him a child." To be sure, advocates of environmental limitations today do not endorse the racist views of the past, but they still regard the original inhabitants of the Amazon as trapped in their environment like flies in amber. Meggers's "law of environmental limitation of culture," her critics in essence say, is nothing but a green variant of Holmberg's Mistake.

Over time, the Meggers-Roosevelt dispute grew bitter and personal; inevitable in a contemporary academic context, it featured charges of colonialism, elitism, and membership in the CIA. Particularly vexing to Meggers was that some of the same people who demanded minutely detailed proof for pre-Clovis sites had cheerfully accepted Roosevelt's revisionism about Marajo. A big, prosperous city rising up on its own in the stifling Amazon forest? Meggers could not contain her disbelief. "I wish a psychologist would look into this," she said to me.

Meanwhile, Roosevelt went on to Painted Rock Cave. On the cave floor what looked to me like nothing in particular turned out to be an ancient midden: a refuse heap. Roosevelt's team slowly scraped away sediment, traveling backward in time with every inch. Even when the traces of human occupation ceased, they kept digging down. ("You always go a meter past sterile," she told me.) A few inches below what she had thought would be the last layer of human habitation she hit another-a culture, Roosevelt said later, that wasn't supposed to be there. It was as much as thirteen thousand years old.

Painted Rock Cave was occupied at roughly the same time that the Clovis culture was thriving to the north. But Amazon paleo-Indians didn't live in the same way as their northern counterparts, Roosevelt said. They didn't make or use Clovis points. They didn't hunt big game (almost none exists in the Amazon). Instead they plucked wild fruits from the forest, painted handprints on the walls, and ate the Amazon's 1,500 species of fish, especially the 500-pound pirarucu, the world's biggest freshwater fish. And then, after 1,200 years, these early people left the cave for good.

Painted Rock Cave became inhabited again in about 6000 B.C. Probably it was no more than temporary shelter, a refuge when floodwaters got too high. People could have brought in loads of turtles and shellfish, built a fire in the shelter of the cave, and enjoyed the feel of dry land. In any case these people-Roosevelt called them the Paituna culture, after a nearby village-had ceramic bowls, red- to gray-brown. Found at Painted Rock Cave and other places in the area, it is the oldest known pottery in the Americas.

And so there were two occupations: one very old, with ceramics; the other even older, without them. To Roosevelt, the first settlement of Painted Rock Cave demonstrated that the Amazon forest was not settled by a copy or offshoot of Clovis. This early culture was a separate entity-another nail in the coffin of the Clovis-as-template theory, to her way of thinking. The second occupation, with its early and apparently independent development of ceramics, demonstrated something equally vital: Amazonia was not a dead end where the environment ineluctably strangled cultures in their cradles. It was a source of social and technological innovation of continental importance.

By about four thousand years ago the Indians of the lower Amazon were growing crops-at least 138 of them, according to a recent tally. The staple then as now was manioc (or cassava, as it is sometimes called), a hefty root that Brazilians roast, chop, fry, ferment, and grind into an amazing variety of foods. To this day, no riverside table is complete without a bowl of farofa: crunchy, toasted manioc meal, vaguely resembling grated Parmesan cheese, which Amazonians sprinkle on their food with abandon. To farmers, manioc has a wonderful advantage: it can grow practically anywhere, in any conditions. In Santarem I met a woman who told me that the asphalt street in front of her home had just been ripped up by the municipal authorities. Underneath the pavement, which had been laid down years before, was a crop of manioc.

Manioc has always been the Amazonian staple. To this day, it is ubiquitous in the slash-and-burn plots that surround every riverside hamlet. These little, shifting farms look like unchanged remnants of the past. But that idea apparently is mistaken. Rather than being the timeless indigenous adaptation portrayed in ecology textbooks, many archaeologists now view slash-and-burn agriculture as a relatively modern technique whose spread was driven by European technology. The main reason is the stone ax.

Living in the world's thickest forest, the inhabitants of the Amazon basin had to remove a lot of trees if they wanted to accomplish practically anything. For this task the stone ax was their basic tool. Unfortunately, stone axes are truly wretched tools. With a stone ax, one does not so much cut down a tree as use the ax to beat a section of the trunk to pulp, weakening the base until the tree can no longer support itself. In the outskirts of the central Amazonian city of Manaus, a researcher let me whack at a big Brazil nut tree with a locally made replica of a traditional stone ax. After repeated blows I had created a tiny dent in the cylindrical wall of the bole. It was like attacking a continent. "Those things suck," the researcher said, shaking his head.

In the 1970s Robert Carneiro, of the American Museum of Natural History, measured the labor required to clear a field before the advent of steel. He set people to work with stone axes in thickly forested parts of Peru, Brazil, and Venezuela. Many of the trees were four feet in diameter or more. In Carneiro's experiments, felling a single four-foot tree with an indigenous stone ax took 115 hours-nearly three weeks of eight-hour days. With a steel ax, his workers toppled trees of similar size in less than three hours. Carneiro's team used stone axes to clear about an acre and a half, a typical slash-and-burn plot, in the equivalent of 153 eight-hour days. Steel axes did the job in the equivalent of eight workdays-almost twenty times faster. According to surveys by Stephen Beckerman, an anthropologist at Pennsylvania State University, Amazonian slash-and-burners are able to work their plots for an average of three years before they are overwhelmed. Given that farmers also must hunt, forage, build houses and trails, maintain their existing gardens, and perform a hundred other tasks, Carneiro wondered how they could have been able to spend months on end banging on trees to clear new fields every three years.

Unsurprisingly, people with stone implements wanted metal tools as soon as they encountered them-the prospective reduction in workload was staggering. When Columbus landed, according to William Balee, the Yanomamo lived in settled villages in the Amazon basin. Battered by European diseases and slave raiding, many fled to the Orinoco, becoming wandering foragers. In the seventeenth century they acquired steel tools, and used them to make the return journey from seminomadic hunter-gatherers to agriculturalists who lived in more or less permanent villages. So precious did European axes become during this time, according to Brian Ferguson, an anthropologist at Rutgers University, that when a source appeared the Yanomami would relocate whole villages to be near it. Steel tools, he told me, "had a major, transformative effect on all the trade and marriage relations in a whole area. They led to new trade networks, they led to new political alliances, they even led to war." Researchers have often described the Yanomamo as "fierce," aggressive sorts whose small villages are constantly at violent odds with one another. In Ferguson's estimation, one cause of the endemic conflict observed by Western anthropologists and missionaries was the anthropologists and missionaries themselves, who gave their subjects "literally boatloads" of steel tools-axes, hatchets, machetes-to ingratiate themselves. At a stroke, the village hosting the Westerners would gleam with wealth; its neighbors would seek a share of the undeserved bounty; conflict would explode. "Steel to the Yanomamo was like gold for the Spanish," Ferguson said. "It could push fairly ordinary people to do things that they wouldn't consider doing otherwise." (The anthropologists and missionaries there vehemently deny Ferguson's claims. But so far as I am aware they did not call his scenario impossible. Rather, they said that to avoid unhappy consequences they had carefully controlled the amount of gift giving.) Metal tools largely created slash-and-burn agriculture, William M. Denevan, the Wisconsin geographer, told me. "This picture of swidden as this ancient practice by which Indians kept themselves in a timeless balance with Nature-that is mostly or entirely a myth, I think. At least there's no evidence for it, and a fair amount of evidence against it, including the evidence of simple logic." Slash-and-burn, supposedly a quintessentially Amazonian trait, "is a modern intrusion."

A similar phenomenon seems to have taken place in North America, where Indians were widely said to have practiced slash-and-burn as part of their habit of living lightly on the land. Dismissing the data to back up these claims as "gossamer," the geographer William E. Doolittle of the University of Texas noted in 2000 that most colonial accounts showed Indians clearing their fields permanently, even ripping stumps out to prevent them from sprouting. "Once fields were cleared, the intent was to cultivate them permanently, or at least for very long periods of time." As populations rose, "farmers cleared new fields from the remaining forests." Slash-and-burn was a product of European axes-and European diseases, which so shrank Indian groups that they adopted this less laborious but also less productive method of agriculture.

In the Amazon, the turn to swidden was unfortunate. Slash-and-burn cultivation has become one of the driving forces behind the loss of tropical forest. Although swidden does permit the forest to regrow, it is wildly inefficient and environmentally unsound. The burning sends up in smoke most of the nutrients in the vegetation-almost all of the nitrogen and half the phosphorus and potassium. At the same time, it pours huge amounts of carbon dioxide into the air, a factor in global warming. (Large cattle ranches are the major offenders in the Amazon, but small-scale farmers are responsible for up to a third of the clearing.) Fortunately, it is a relatively new practice, which means it has not yet had much time to cause damage. More important, the very existence of so much healthy forest after twelve thousand years of use by large populations suggests that whatever Indians did before swidden must have been ecologically more sustainable.

RAINDROP PHYSICS.

The papaya orchard was so robust and healthy that it looked like an advertisement-the background image behind a celebrity endorser of a new papaya drink. Sweating in the equatorial sun, some of the researchers admiringly fingered the plump, pendulous green fruit, each the size of a baby's head, wrapped in clusters around the trees' sturdy trunks. Other scientists bent down and with equal approbation scooped up handfuls of dirt. The road to the plantation had been cut into the Amazon's famously poor soil-it was the blaring orangered of cheap makeup, almost surreally bright against the great dark green leaves of the forest. But in the shade of the papaya trees the soil was dark brown, with the moist, friable feel that gardeners seek.

At first glance, the soil seemed similar to what one would find in, say, the grain belts of North America or Europe. After a more careful inspection, though, it looked entirely different, because it was full of broken ceramics. The combination of good soil, successful agriculture, and evidence of past Indian inhabitation was what had brought the scientists to the farm. I had been invited to tag along.

The orchard was about a thousand miles up the Amazon, two hours by ferry and bus from Manaus. Manaus, the biggest city on the river, is situated on the north bank of the Amazon, hard by its junction with the Negro River, a major tributary.*24 Between the two rivers is a tongue of land that, depending on your point of view, is either almost destroyed by development or quite lightly inhabited considering its proximity to a city of a million people. Near the tip of the tongue is the small village of Iranduba: a bush-pilot airport, a half-dozen lackadaisical stores, some bars with jukeboxes loud enough to knock birds from the trees, and docks for loading local farmers' produce. A few miles outside Iranduba, on a bluff above the Amazon, stood the papaya orchard. It was one of the many small riverside farms operated by the descendants of Japanese immigrants.

In 1994 Michael Heckenberger, now at the University of Florida in Gainesville, and James B. Petersen, now at the University of Vermont in Burlington, decided to look for potential archaeological sites in the central Amazon. With a team of Brazilian scientists, Meggers had surveyed much of the river and its tributaries in the 1970s and 1980s and concluded there was little of archaeological relevance-further proof of the inescapability of ecological constraints. Believing that Meggers's survey had been too coarse-grained, Heckenberger and Petersen decided to search a single area intensively. Joined by Eduardo Goes Neves of the University of So Paulo, several dozen of Neves's students, and, later, Robert N. Bartone, of the University of Maine at Farmington, they found more than thirty sites at the Amazon-Negro junction, four of which they excavated fully. The papaya farm was one of the four. Now Neves, Petersen, and Bartone were leading a score of visiting researchers and a journalist on a tour of the site.

From the shade of a doorway, the father of the family watched us mill around with a tolerant smile. A teenage girl stood outside, listlessly sweeping at a cloud of yellow butterflies. Through the loosely placed boards in the wall floated the bark and jabber of a talk-radio show about the latest soccer perfidy from Argentina, Brazil's hated rival. Although it was winter, the midday sun was hot enough to make sweat start out from the skin.

At the edge of the papaya grove were ten low earthen mounds that the team had identified as human-made. Carbon dating indicated that they were constructed in about 1000 A.D. The archaeologists had begun opening up the largest of the mounds. Already they had discovered nine burials, one body placed in a big funerary urn, all apparently interred at the same time. Because the scientists were unlikely to have uncovered the area's only concentration of human remains in their first, exploratory test pit, they believed that the entire mound was likely to be full of burials-hundreds of them. "That suggests thousands of people lived here," Neves said. "In 1000 A.D., that's a big place."

Shoving back his baseball cap, Neves levered himself into the excavation site, a six-foot, rectangular hole with the right-angled corners and precisely vertical walls that are a hallmark of archaeological investigation. One of the visiting researchers passed down a Munsell soil-color chart. Resembling strips of paint-color samples, these are used by pedologists (soil scientists) to classify soils. Neves scraped the wall lightly, exposing fresh earth, and pinned the chart to the wall with a big-headed nail. From the top of the dig he dangled a measuring tape-alternating ten-centimeter strips of red, white, and green-to indicate depth. Digital cameras ratcheted and whined. It was a vest-pocket version of the inspection of Folsom by the graybeards.

Neves had a little trouble hanging the tape because he couldn't find a place where it wouldn't get snagged on the broken ceramics protruding from the walls. They bristled from the side of the dig in a profusion that reminded me of the Beni mounds, hundreds of miles upstream. Some of the pieces seemed to form horizontal layers. As in the Beni, the ceramics had apparently been smashed deliberately, perhaps to build up the surface.

I asked Petersen, a ceramics specialist, how many plates and bowls and cups were in the mounds. He pulled out a scrap of paper and a pen and scribbled some numbers. In a minute or two he looked up. "This is a rough, back-of-the-envelope-type estimate," he warned, showing me the result: the single mound we were standing on might contain more than forty million potsherds. "Think of the industry required to produce that much pottery," Neves said. "Then they just smash it. Look at the way they piled up this good soil [to make the burial mound]-it's all wasteful behavior. I don't think scarcity was a problem here."

The ecological constraints on tropical soils are in large part due to the gravitational energy of raindrops. Rainfall, drumming down day in and day out, pounds the top few inches of earth into slurry from which nutrients are easily leached and which itself easily washes away. In uncut forest, the canopy intercepts precipitation, absorbing the physical impact of its fall from the clouds. The water eventually spills from the leaves, but it hits the ground less violently. When farmers or loggers clear the tree cover, droplets shoot at the ground with more than twice as much force.

Slash-and-burn minimizes the time in which the ground is unprotected. Intensive agriculture is much more productive but maximizes the land's exposure. This painful trade-off is why ecologists argue that any attempt by tropical forest societies to grow beyond small villages has always been doomed to fail.

According to Charles R. Clement, an anthropological botanist at the Brazilian National Institute for Amazon Research (INPA) in Manaus, though, the first Amazonians did avoid the Dilemma of Rainfall Physics. Speaking broadly, their solution was not to clear the forest but to replace it with one adapted to human use. They set up shop on the bluffs that mark the edge of high water-close enough to the river to fish, far enough to avoid the flood. And then, rather than centering their agriculture on annual crops, they focused on the Amazon's wildly diverse assortment of trees.

In his view, the Amazon's first inhabitants laboriously cleared small plots with their stone axes. But rather than simply planting manioc and other annual crops in their gardens until the forest took them over, they planted selected tree crops along with the manioc and managed the transition. Of the 138 known domesticated plant species in the Amazon, more than half are trees. (Depending on the definition of "domesticated," the figure could be as high as 80 percent.) Sapodilla, calabash, and tucuma; babacu, acai, and wild pineapple; coco-palm, American-oil palm, and Panama-hat palm-the Amazon's wealth of fruits, nuts, and palms is justly celebrated. "Visitors are always amazed that you can walk in the forest here and constantly pick fruit from trees," Clement said. "That's because people planted them. They're walking through old orchards."

Peach palms-the trees through which I looked at the Amazon from Painted Rock Cave-are Clement's favorite example. Giddily tall and straight, they have up to a dozen stalks, with a protective mat of spikes wrapped around the bottom of the tree. The protection is little needed; peach palm wood is hard enough that in the Beni it was used for saw blades. Bundles of orange or red fruit hang like clusters of bocce balls from the base of the fronds. The fruit is soaked with oil and rich in beta-carotene, vitamin C, and, surprisingly, protein. When dried, the white or pink pulp makes flour for thin, tortilla-like cakes; when boiled and smoked, it becomes hors d'oeuvres; when cooked and fermented, it makes beer. (The sap also makes a kind of wine.) Two crops a year are not uncommon; in terms of yield per acre, peach palms are typically much more productive than rice, beans, or maize. Trees begin producing fruit after three to five years and can continue for another seventy years. Like strawberries, peach palm throws out adventitious shoots. With a little care, these can be harvested for heart-of-palm-very tasty heart-of-palm, in my experience. Bactris gasipaes, as scientists call it, has more than two hundred common names: pupunha, cahipay, tembe, pejibaye, chontaduro, pijuayo. To Clement, the proliferation of names suggests the plant was used for many purposes by many cultures.

In the 1980s and early 1990s Clement measured peach palms throughout the Amazon basin. He learned that several physical characteristics, including fruit size, lay on a gradient with those apparently closest to the wild state in western Amazonia, near the Beni; the implication was that the tree might first have been cultivated there. Using a different method, Jorge Mora-Urpi, one of Clement's collaborators, concluded that Indians might have bred the modern peach palm by hybridizing palms from several areas, including the Peruvian Amazon. Whatever the origin, people domesticated the species thousands of years ago and then spread it rapidly, first through Amazonia and then up into the Caribbean and Central America. Bactris gasipaes was in Costa Rica 1,700 to 2,300 years ago and probably earlier. By the time of Columbus, one seventeenth-century observer wrote, Native Americans valued it so highly "that only their wives and children were held in higher regard."

Unlike maize or manioc, peach palm can thrive with no human attention. Tragically, this quality has proven to be enormously useful. In the seventeenth and eighteenth centuries many Amazonian Indians, the Yanomamo among them, abandoned their farm villages, which had made them sitting ducks for European diseases and slave trading. They hid out in the forest, preserving their freedom by moving from place to place; in what Balee calls "agricultural regression," these hunted peoples necessarily gave up farming and kept body and soul together by foraging. The "Stone Age tribespeople in the Amazon wilderness" that captured so many European imaginations were in large part a European creation and a historical novelty; they survived because the "wilderness" was largely composed of their ancestors' orchards. "These old forests, called fallows, have traditionally been classified as high forest (pristine forest on well-drained ground) by Western researchers," Balee wrote in 2003. But they "would not exist" without "human agricultural activities." Indeed, Amazonians typically do not make the distinction between "cultivated" and "wild" landscapes common in the West; instead they simply classify landscapes into scores of varieties, depending on the types of species in each.

After we had spoken for a while Clement took me out of his office and into INPA's experimental forest. To my untrained eye, it looked much the same as the forests around the lodges outside Manaus that attract ecotourists, except that INPA staffers kept down the undergrowth. There was the same cool green light from the canopy, the same refulgent smell, the same awe-inspiring sense of variety. The air vibrated with the same inharmonic racket of squealing, burbling, croaking, and cheeping birds. Dribbling down some of the tree trunks were little runnels that looked like dried sap. On a previous visit to the Amazon I had seen runnels just like these on a rubber tree in an abandoned plantation. Thinking it was a drip of latex sap, I plucked at one. It was the cover for a termite superhighway. Termites boiled out of the little tunnel and all over my hand. Termites bite. Flapping my hand wildly, I leapt back from the tree. My sandaled foot landed on a ground-wasp nest. In this way I learned why some Amazonians have a jaundiced view of biodiversity. On Clement's tour I kept my hands to myself.

It was July-winter in the Amazon, the worst time of the year for fruit. Nevertheless, Clement was able to find yellow bacuri and purple acai. He plucked what looked like a four-foot version of a string bean from a branch, split it lengthwise, and showed me flattened, shiny seeds arrayed along its length like teeth in a jaw. Each seed was the size of a thumb bone and nestled in a fluffy white coating. "Try this," he said. "It's the ice-cream bean." I put a seed in my mouth and sucked on it. The coating did taste quite like vanilla ice cream, and was just as refreshing. Three or four more fruits followed, each equally strange to me. (This is what people like about biodiversity.) Peach palm was not in season, but he found another member of the same genus. The fruit, when peeled, was unappetizing-quite like soggy cardboard in color, texture, and flavor. Clement squeezed some pulp. Oil dribbled from his fingers to the ground. "This'll put some calories into you," he said.

Planting their orchards for millennia, the first Amazonians slowly transformed large swaths of the river basin into something more pleasing to human beings. In the country inhabited by the Ka'apor, on the mainland southeast of Marajo, centuries of tinkering have profoundly changed the forest community. In Ka'apor-managed forests, according to Balee's plant inventories, almost half of the ecologically important species are those used by humans for food. In similar forests that have not recently been managed, the figure is only 20 percent. Balee cautiously estimated, in a widely cited article published in 1989, that at least 11.8 percent, about an eighth, of the nonflooded Amazon forest was "anthropogenic"-directly or indirectly created by humans.

Some researchers today regard this figure as conservative. "I basically think it's all human created," Clement told me. So does Erickson, the University of Pennsylvania archaeologist who told me in Bolivia that the lowland tropical forests of South America are among the finest works of art on the planet. "Some of my colleagues would say that's pretty radical," he said. According to Peter Stahl, an anthropologist at the State University of New York in Binghamton, "lots" of researchers believe that "what the eco-imagery would like to picture as a pristine, untouched Urwelt [primeval world] in fact has been managed by people for millennia." The phrase "built environment," Erickson argued, "applies to most, if not all, Neotropical landscapes."

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 indio-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 Santarem 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 Belem, 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 Kayapo, 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 Kayapo 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 Kayapo 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 Tupi-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 Rio 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 Xingu, a long Amazon tributary with its headwaters deep in southern Brazil. People had lived around the Xingu 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 Tupi-Guarani 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."