The search for El Dorado, that mythical basin of gold told by Spanish conquistador Francisco de Orellana in 1542 did not yield what Orellana described as a hidden city of gold with a network of farms, villages, and huge walled cities.

Many explorers then and scientists today believe that there really is no city of gold. In fact, even the farms and villages that Orellana described could not be found in the Amazon because as productive as forest soils may be, they could not support intensive agriculture, as described by the Conquistador. Soil tests and even farming trials have been done in the Amazon to support this claim and even modern chemicals and treatments could not make the soil productive enough to support a thriving city, golden or not.

But scientists have also found patches of what could have been huge settlements in the Bolivian savannah. This place is now a dead man's area, flooded during the wet season, fire burdened during the dry. No agriculture exists but scientists have found some interesting patches of land that suggests high agricultural activity and therefore human communities.

Could the tale told by Orellana therefore be true? Could interconnected villages really exist in the Amazon area? Were tribes supporting a complex social system really there? Could the golden city be more than just a romanticized story?

The answer to the secret ladies and gentlemen, lies in the soil.

It looks like the probable places where human communities in the Amazon existed had one thing in common --- darker soil. Upon closer examination, scientists have uncovered that the soil where civilized communities existed and those that did not were the same, and the dark color was a result of human activity specifically, the addition of biological matter.

Brazilians calls the dark soil Terra Preta and is known for its productivity. The area where Terra Preta was discovered is huge (estimated at twice the size of the UK) which meant that the people of the famed El Dorado city transformed soil into its weight in gold.

These ancient environmentalists and soil scientists are now gone. You can insert your hypotheses here (they may have been killed by diseases, forced to war, abducted by aliens, etc.) but one thing is certain. They have made the soil better and more productive. And now we are discovering that this ancient approach to soil improvement may be a sustainable way of helping mitigate pollution and harmful environmental concerns.

One more post on this fascinating subject tomorrow!