Did people make the Amazon's black earth, and was the rainforest ever wild?
Hidden in the poor soil of the Amazon are patches of black, fertile earth full of potsherds, made by people long before Columbus.
▶ Start the storyTerra preta, Portuguese for "black earth", is a very dark, fertile soil found in the Amazon basin, and much of it, at least, was made by people. It owes its black color to charcoal, and it was made by adding a mixture of charcoal, bones, broken pottery, compost and manure to the poor Amazonian soil. The charcoal is stable and stays in the soil for thousands of years, binding and holding on to minerals and nutrients. Because of that, terra preta is less prone to nutrient than the surrounding soil.
It was created by farming communities before Europeans arrived, between about 450 BCE and 950 CE, and it can be up to 2 metres deep. Some measurements found up to 9 percent black carbon in terra preta, against 0.5 percent in the soils around it.
Terra preta
- Dark, full of charcoal and potsherds
- Holds nutrients, resists
- Up to 9% black carbon
Surrounding soil
- Infertile, easily leached
- Pale and poor
- About 0.5% black carbon
Why does that matter? For a long time, scientists thought that the poor soil meant the Amazon could never have held many people. The archaeologist Betty Meggers argued that no more than 0.2 people per square kilometre could be sustained by hunting, and that farming was needed to support more. But recent findings suggest the region was densely populated. Some 5 million people may have lived in the Amazon around 1500. The Spanish explorer Francisco de Orellana reported densely populated regions stretching for hundreds of kilometres. He may have exaggerated, although that is disputed, but numerous found on deforested land have supported the idea of large past societies.
That led to a surprising view. The BBC series Unnatural Histories presented evidence that the Amazon has been shaped by people for at least 11,000 years through practices such as forest gardening and terra preta. Researchers still debate how much of it was made on purpose, and how much terra preta there is: estimates run from 0.1 percent of the forest to 10 percent or more. What is clear is that the story ended in tragedy. The societies that made it vanished after the demographic collapse of the 16th and 17th centuries, caused by European diseases such as smallpox and by slave-raiding.
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Recap
People once fed poor soil with charcoal and waste, and the result is a black earth that has kept its fertility for centuries.
💡 A trick to remember it · Charcoal is a sponge that never wears out: soak it in kitchen scraps and a poor soil stays rich for a thousand years.
Surprising fact · Some terra preta holds up to 9 percent black carbon, against 0.5 percent in the soils around it.
Sources (2)
No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.