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24 September 2014
Science & Nature: TV & Radio Follow-upScience & Nature
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The Kuikuru Amerindians are part of an Amazonian anthropological puzzle
BBC Two, Thursday 19 December, 9pm
The Secret of El Dorado
Coming up on Horizon
Isolated in mid-Pacific, get inside The Mystery of Easter Island.

The Secret of El Dorado - questions and answers

Is there only one account (Francisco de Orellana's) that refers to an Amazonian El Dorado?

Orellana actually never mentions El Dorado by name. He was part of an expedition to find a wealthy kingdom in the jungles of present day Ecuador. The Conquistadors had heard the Indians tell of such a kingdom, but it's not clear that they associated it with the legend of El Dorado ('the gilded one'). He and his men became separated from the main group and swept into the Amazonian river system. They floated all the way to the Atlantic, describing many large kingdoms, towns and even cities along the way. Orellana (or rather his chronicler, the expedition's priest, Gaspar de Carvajal) claimed that the Indians talked of kingdoms further inland where there was much gold, but he never claimed to have seen any himself. It was twenty years before any other Europeans attempted to explore the central Amazon, and their accounts of the region are very different.

Is it archaeologists' belief that the Amerindians did not build huge structures or is the erosion in the Amazon greater than that further north where - for example - Mayan temples still stand?

There is practically no stone in the Amazon Basin, and so the Amazonians built in wood. Of course, this quickly decays in the tropics - in just a few years it's all eaten by insects. The Amazonians did move earth on a large scale, however, and some very impressive monuments are now coming to light as areas of forest are cleared. The mounds and causeways are difficult to discern under forest canopy, of course.

Over what historical time period does the generation of terra preta (the fertile, artificial, dark earth) extend?

Eduardo Neves has been using radiocarbon dating to date terra preta sites. So far a clear pattern emerges - the terra preta seems to start around the time of Christ, perhaps a few hundred years earlier. This is the same time that archaeologists first see complex polychrome pottery and evidence of mound building, both in the Llanos de Mojos and on Marajó island at the mouth of the Amazon.

How valid is it to extrapolate from aerial mapping of terra preta plots to areas of civilisation?

Most archaeologists now agree that terra preta is an anthrosol, ie an artificial soil. So there is little doubt that where there is terra preta there was once human activity.

Can we be sure people weren't nomadically wandering from one terra preta mound to another, ie that fewer people were being supported by the soil?

Again, Eduardo Neves has used carbon dating to estimate the rate of terra preta formation. He finds that a metre of soil was produced in just a few decades. This is a very fast rate of soil formation, and Neves believes that this is evidence that the occupation that produced it was intense and continuous. It's fair to say that some scientists take a different view. Betty Meggers in particular holds to the view that the occupation was sporadic and shifting, and that very high population estimates are therefore unjustifiable. This is probably the minority view today.

How long does terra preta take to develop from normal jungle/savannah earth?

We have yet to succeed in making terra preta ourselves, but perhaps we could do it faster than the Indians if we can get to understand what the key ingredients are.

Is there anything at all special about the charcoal that seems to create terra preta?


What has been the attitude of governments etc in the Amazon region to these studies?

The Brazilian government has been making increasing efforts in recent years to preserve and protect its native patrimony. IMBRAPA, the government-funded agricultural research institute is now heavily involved in terra preta research.

Who will benefit most if the bio/chemical secret of terra preta is ultimately unlocked?

It could have profound effects on tropical agriculture, especially in light of a worldwide crisis in soil fertility. Terra preta seems especially suitable for the cultivation of fruit and vegetables, what we would call market gardening. These crops have high economic and nutritional value for poor farmers in the developing world, and they would be the main beneficiaries if it could be recreated on a wide scale. There would be environmental benefits as well. Modern agriculture in the Amazon requires heavy annual input of chemical fertilizers, and the run-off from these is now causing problems in the rivers. This is a big problem for the Kuikuru for example in the Upper Xingu valley. So called eutrophication kills fish, and the Kuikuru rely on fishing for the protein in their diet. Better soil would mean less fertilizer and healthier rivers.

What evidence is there that terra preta 'technology' is applicable the world over?

The problem with tropical soils is essentially the same all over the world. The high levels of rainfall over hundreds of thousands of years remove all the nutrients from the soil leaving only a clay substrate. This clay lacks the chemical ability to hold on to nutrients, even if they are added. This is why fertiliser doesn't work very well, and why the charcoal may be so effective. As you may know if you take charcoal tablets for a stomach upset, charcoal is very good at absorbing things!

Can terra preta become an export 'crop' for Amerindian people instead of hardwood etc?

It's more likely that it would be made in situ than exported.

University of Vermont
Rainforest fertility
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