We have posted
extensively on Terra Preta. This item
shows us that the archeology is beginning to pick up steam. The original discovery came from
archeological work. The good news is
that presence of Terra Preta is a clear marker of human settlement and by that
I mean a serious agricultural population able to actually build out
substantially. We also know this was all
intact at the time of first contact.
However, disease and
technological collapse took place long before significant European penetration
could take place. This also happened
throughout the Americas and we are left with scant eye witnesses.
This remains the one
place in which populations of the tens of millions was both possible and with
Terra Preta, technically plausible.
Searching
for the Amazon's hidden civilizations
Look
around the Amazon rainforest today and it’s hard to imagine it filled with
people. But in recent decades, archaeologists have started to find evidence
that before Columbus’s arrival, the region was dotted with towns and perhaps
even cities. The extent of human settlement in the Amazon remains hotly
debated, partly because huge swaths of the 6-million-square-kilometer
rainforest remain unstudied by archaeologists. Now, researchers have built a
model predicting where signs of pre-Columbian agriculture are most likely to be
found, a tool they hope will help guide future archaeological work in the
region. Big picture. A new model of the Amazon predicts that terra preta is
more likely to be found along rivers in the eastern part of the rainforest. The
letters indicate known archaeological sites [Credit: Crystal McMichael]
In
many ways, archaeology in the Amazon is still in its infancy. Not only is it
difficult to mount large-scale excavations in the middle of a tropical
rainforest, but until recently, archaeologists assumed there wasn’t much to
find. Amazonian soil is notoriously poor quality—all the nutrients are
immediately sucked up by the rainforest’s astounding biodiversity—so for many
years, scientists believed that the kind of large-scale farming needed to
support cities was impossible in the region. Discoveries of gigantic earthworks
and ancient roads, however, hint that densely populated and long-lasting
population hubs once existed in the Amazon.
Their
agricultural secret? Pre-Columbian Amazonians enriched the soil themselves,
creating what archaeologists call terra preta. Terra preta—literally “black
earth”—is soil that humans have enriched to have two to three times the
nutrient content of the surrounding, poor-quality soil, explains Crystal
McMichael, a paleoecologist at the Florida Institute of Technology in
Melbourne. Although there is no standard definition for terra preta, it tends
to be darker than other Amazonian soils and to have charcoal and pre-Columbian
pottery shards mixed in.
Most
of it was created 2500 to 500 years ago. Like the earthworks, terra preta is
considered a sign that a particular area was occupied by humans in the
pre-Columbian past. By analyzing location and environmental data from nearly
1000 known terra preta sites and comparing it with information from soil
surveys that reported no terra preta, McMichael and her team found patterns in
the distribution of the enriched soil. The scientists concluded that terra
preta is most likely to be found in central and eastern Amazonia on bluffs
overlooking rivers nearing the Atlantic Ocean. It’s less common in western
Amazonia, where runoff from the Andes tends to add nutrients to the soil
naturally, and in highland areas such as Llanos de Moxos in Bolivia, which is
home to many impressive pre-Columbian earthworks. By analyzing the
environmental conditions most strongly associated with terra preta, the team
was able to build a model predicting where undiscovered terra preta sites are
most likely to be found.
Overall,
they suspect that there is probably about 154,063 km2 of terra preta in the
Amazon, composing about 3.2% of the basin’s total area, they report online
today in the Proceedings of the Royal Society B. Not only does modeling the
likely locations of terra preta reveal possible patterns of human settlement in
the Amazon, but it also gives archaeologists “a starting point” for future
excavations, McMichael says. “Within a forest of almost 6 million square
kilometers, it’s hard for archaeologists to determine site locations for
sampling,” she explains. Like the increasingly popular LiDAR—which can find
earthworks hidden under the rainforest canopy but can’t sniff out terra
preta—“these [statistical] methodologies narrow down the probabilities” of
where to find promising archaeological sites.
Other
Amazon experts are more skeptical. Michael Heckenberger, an archaeologist at
the University of Florida in Gainesville, who was not involved in the research,
points out a possible discrepancy in the sampling methods employed by
McMichael’s team. The terra preta sites used to make the statistical model, he
says, “just happen to be the areas where there’s been intensive archaeological
survey.” The areas designated as terra preta-free, on the other hand, were
sampled and categorized by ecologists and geologists, often long before anyone
was looking for terra preta or other signs of pre-Columbian settlements in the
Amazon.
Just
because a region is labeled terra preta-free now, Heckenberger suspects,
doesn’t mean there isn’t any terra preta there. It just means archaeologists
haven’t been there to look for it—yet. McMichael’s map “serves as a reminder of
what we don’t know” about the Amazon’s past, he says. McMichael agrees that a
terra preta-free label should not be taken as proof that humans never settled a
region. The relative lack of terra preta around the Llanos de Moxos earthworks
proves that humans didn’t necessarily enrich the soil, or do so in the same
way, everywhere they lived, she says. “I would think that cultures adapted
differently to the different environmental conditions,” creating terra preta
where the natural soil was particularly poor and modifying their environment in
other ways in regions where they didn’t necessarily need to enrich the soil to
support large populations.
McMichael
hopes to use her statistical methods to model all different kinds of ancient
human impacts on the Amazon. Her team has a paper in press at the Journal of
Biogeography predicting the locations of earthworks, and eventually she hopes to
create a map correlating past human settlements with various ecological
patterns. If pre-Columbian humans encouraged the spread of particular plants
and animals they found helpful in the regions around their settlements, for
example, that might affect species distribution in the Amazon today. Soon,
scientists might be able to go beyond earthworks and agriculture and read the
Amazon’s history in the forest itself.
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