[Terrapreta] The Science of Terra Preta Formation

[Jim Joyner]

If I might add a few things:

I find it very difficult to believe that dark earth in Amazonia had a 
natural start. Much of the muck soils in the US Midwest were due to 
catastrophic events through the ice ages. These nutrients became a 
treasure trove of nutrients that farmers are still mining. There is 
nothing comparable in the tropics that I know of. (Well, there the 
occasional guano deposits found, but even these are not soils)

There is practically no way that carbon can naturally accumulate in the 
tropics for any length of time. The one exception to that seems to be 
charcoal but that is not what we would call natural.

Also, in terms of nutrient (I'm speculating, but bear with me). For 
thousands, many hundreds of thousands of years, nutrient  has flowed 
into the Amazon from the mountains above. Some of these nutrients are 
soaked up into above ground jungle/rain forests. Some, of course, are 
bound up in aquatic life. Most are washed out to sea. But there is no 
source of nutrient in the tropics to "mine" like there are in the 
temperate zones. There is no soil deposit to mine simply because, if it 
had existed, it would  have quickly disappeared.

This means, I think, to have supported what seems to have been huge 
populations, there had to be a serious form of economizing and cycling 
of nutrient. Basically, people had to take from the rivers and some from 
the forests (so far that is gather-hunting which will not support large 
populations), but in time as they keep their waste (somehow), they 
recycled and accumulated nutrient. This recycling is not unusual (Asians 
ahve done for millenia), but it is difficult in the tropics simply 
because the medium that is necessary (for the most part) to hold these 
nutrients, in a usable way, is carbon. And most carbon under normal 
natural conditions in the tropics will will simply evaporate (actually, 
the process is burning or oxidation).

Somehow, it seems the people discovered a medium to collect, hold and 
recycle nutrients and carbon. Our guess, of course, some form of char.

Jim