December 18th, 2010

[LINK] "Terra Preta, or, The Lost Cities of Amazonia"

Was there a high civilization in Amazonia, and what suggests its existence? That's the subject of pauldrye's most recent Passing Strangeness post.

One of the many inexplicable statements in historical literature is Gaspar de Carvajal’s description of his travels down the Amazon River with Francisco de Orellana. He says in numerous ways that the banks of the Amazon were stuffed with people, literally village after village for most of its length. No-one else reported this. All subsequent expeditions found the Amazon Basin much as it is today—thinly inhabited. Indeed it had to be this way, as Amazonian soils are notoriously poor for farming. The tragedy of modern-day deforestation of the jungle there is that the poor Brazilian farmers doing the cutting end up with farms that can’t support them for more than a few years before the soil’s nutrients are gone. Even the native Amazonians have to resort to slash-and-burn agriculture, clearing an area then moving on after a while to let the soil recover rather than settling in villages. De Carvajal, like many early explorers, must have been embellishing his tale to the point of lying.

Except maybe not.

De Orellana’s expedition was the first to reach the deep Amazon jungle, in 1541. Surprisingly he began from the west coast of South America, crossing the Andes from the Spanish conquests in Peru and then working his way down to the mouth of the river where the Portuguese had a presence. In between was terra incognita to Europeans. From the end of this expedition in 1542 until until 1637 there were no other trips up or down much of the Amazon (barring the bizarre Pedro de Ursúa and Lope de Aguirre episode two decades later).

Pedro Teixeira was responsible for that new expedition, and he reported a green desert: trees and rampant foliage, and no villages worth mentioning let alone entire civilizations. So it’s been down to the present day: if de Carvajal were telling the truth, the ninety-five years between the two expeditions concealed the death of literally millions of people and an entire way of life.

Disease may well explain the depopulation of Amazonia over a century. What might prove that the region was inhabited? The soil itself.

This leads to terra preta de Indio, or just “terra preta” for short, the Brazilian Portuguese name for an unusual phenomenon. Good farming soils have many silicate particles, which trap the nutrients a growing crop needs. Amazonian soils are low in silicate and high in aluminum and iron oxide; those oxides have the opposite effect to silicate, making nutrients susceptible to leaching when the rain comes down.

But here and there through the Amazon are patches of terra preta (“black soil”) that are extremely fertile despite being low in silicates as well. A high fraction of carbon particles from burned trees and plants, which also have nutrient-trapping properties, take their place. Furthermore, the carbon is buffered from rain by large amounts of crushed pottery mixed all throughout the soil. Some argue that terra preta patches are the remnants of Amazonian waste dumps and so happened by accident; the potsherds are just the broken leftovers of everyday items. Others argue that there’s just too much of it mixed in with the soil—that pre-Colombian Amazonians deliberately made pottery for the sole purpose of smashing it and using it to make farmable plots.

The final answer to this question depends on just how much terra preta there is, and for the moment we just don’t know. Estimates have varied between 6,300 square kilometers spread over the whole Amazon (in which case it’s reasonable to think its creation was an accident) to one hundred times that—in other words, the size of the entire Ukraine, the country with the fifth largest amount of arable land in the world.

Go, read the post in full. It's a great piece of historical summarization and detectivework.
forums, me, non blog

[FORUM] What sorts of surprises do you expect we'll find out about the human past?

I think that the emerging near-certainty that pre-contact Amazonia hosted a high civilization is awesome, both in the sense of the entire concept being a very cool idea (the culture may have systematically terraformed its land!) and in the sense that it was possible for such a large civilization to vanish almost entirely. If the depopulation of the Amazon rain forest could occur with hardly anyone noticing that it had happened for centuries, what else might lie outside of the current realm of human knowledge?

That's the subject of today's [FORUM] post. What sorts of surprising discoveries do you think that current--and future--generations of humans will discover about our species' past? Are there high civilizations--agricultural civilizations, say--unknown to us? (If so, i'd bet that they found their homes on the continental shelves of the world, feritle littoral land in the Ice Ages but drowned now.) Were there writing systems predating Sumeria's cuneiform innovations? What about surprises in the history of the Earth, or the Solar System? (Are we the first sophonts, really, or as suggested in The Science of Discworld are there innumerable curshed species with their own civilizations that never had the chance to take off, or did they?)