How Garbage Fueled Ancient Agriculture

When a couple of archaeologists whose friendship dated back to college days decided to use their vacation to explore the Amazon River basin a few years ago, they had no reason to think they would find much of interest.

Scholars had ruled out the likelihood that prehistoric Indians had made much use of that region because of soil that is so deprived of nutrients that one expert had labeled the Amazon and its many tributaries a "counterfeit paradise."

But what James Petersen and Michael Heckenberger found was so startling that it has helped galvanize researchers around the world and it has refocused attention on that region.

They found traces of a great city that had thrived on the banks of the Amazon more than 1,000 years ago. It may well have been one of the largest cities in the world at that time, with a population of at least 200,000 persons, but it disappeared in the wake of the Spanish conquest. Its many inhabitants became what Science magazine recently called "the forgotten people of Amazonia."

Turning Sand Into Paradise

But what is even more startling is the fact that somehow those early settlers had managed to enrich the soil with nutrients that persisted even to this day, turning what some have called a wet desert into a garden paradise. How they did it, and why the soil remained fertile for centuries despite the punishing heat and torrential rains that normally wash nutrients away, has stumped modern scientists.

They did something that nobody has been able to do since, and if experts can figure out exactly how they did it, vast regions of the planet that are not now suitable for agriculture might spring to life.

Like so many archeological discoveries, parts of this story have been known for years. The rich pockets of soil, known as terra preta do Indio (Indian dark earth) have been used by local farmers for many years because they can grow crops with virtually no fertilizer. And the fact that the hillsides were littered with ancient pottery shards was documented more than a century ago.

But nobody had put it all together before, and bit by bit a fuzzy story of a lost civilization is coming into focus. Petersen, now chair of anthropology at the University of Vermont, and Heckenberger, now at the University of Florida, began kicking around the idea of exploring the Amazon back in the 1980s. Archaeology was not exactly booming in the Amazon, partly because working conditions can be miserable and language barriers abound.

But Heckenberger persevered, becoming fluent in Portuguese and establishing contact with the few archaeologists in Brazil, especially at the University of São Paulo. After completing his doctoral research in the southern part of the Amazon, Heckenberger turned once again to his old friend.

"He said let's get a project going in the heart of the Amazon," Petersen says. "We went there on holiday in 1994 and found an archaeological site just by talking with local people."

Packed City

The people told them of pottery shards on a riverbank near the village of Acutuba, near the confluence of the Amazon and the Rio Negro, but when the two Americans began poking in the soil they were astonished. They found bits of pottery everywhere.

"It's just unbelievable," Petersen says. "Unbelievable."

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