Posted on 05/07/2026 7:33:29 PM PDT by Red Badger
Dark earth, the strange patches of black soil rich in nutrients that cause plants to grow at accelerated rates, while also capturing unusually high amounts of carbon from the air, is one of the Amazon rainforest’s greatest mysteries.
Since these patches of dark earth were first discovered by European colonizers in the 1880s, debate has raged over their origins, with ideas ranging from the natural to the artificial.
Variants of this dark, nutrient-rich soil have been found in a range of locations around the world, and are most often associated with the accumulation of materials in soil after long periods of human settlement. In the Amazon, the dark earth variant is locally known as terra preta do índio, “black soil of the Indian,” and bears a characteristically dark coloration that many scientists attribute to the presence of charcoal.
Now, in the face of soil degradation and a carbon-fueled climate crisis, researchers are looking to this ancient soil for solutions to modern problems.
The Effects of Dark Earth
It may come as a surprise that the majority of the soil in the Amazon rainforest is of relatively low quality. Thin and sandy, much of the Amazonian soil allows heavy rains to remove most of its nutrients. However, in the small patches of area known as “dark earth”—usually located near rivers and comprising just a few acres, with estimated ages of more than two millennia—it is vastly more fertile. As one of the world’s richest soils, dark earth holds a relatively high pH value and contains large amounts of nitrogen, potassium, and phosphorus.
Incredibly, trees growing in these dark earth patches are six times the size of those grown in other Amazonian soils, with even their root systems growing far larger than normal. In one experiment conducted in Brazil, University of São Paulo researcher Dr. Anderson Santos de Freitas found that adding just 20% of this dark earth to existing soil doubled crop growth in a struggling region.
Dark earth can also store more than five times the carbon of surrounding soil, accounting for 9 million metric tons, despite making up only 3 to 4 percent of Amazonian soil.
Since its initial discovery in the Amazon, soil reminiscent of dark earth has been identified in other locations globally, on every continent except Antarctica. Yet these forms of dark earth are dated to much more recent periods and have somewhat different chemical makeups.
Indigenous Practices and Dark Earth
The earliest speculations regarding the soil’s origins included volcanic fallout or perhaps the final remains of ancient bodies of water. As the use of scientific instrumentation advanced, analysis of dark earth revealed that it was more similar to compost, consisting of decomposed organic matter such as food waste, manure, and ash, likely representing the accumulated remnants of indigenous life in the region.
However, since most of the region’s indigenous communities have disappeared over the last half millennium due to colonization, determining much about the soil’s origins has remained a challenge.
Of those few groups remaining, the agricultural practices of the Kuikuro people of central Brazil caught the attention of archaeologist Dr. Morgan Schmidt. The Kuikuro people have several practices that could account for dark earth, including peeling their staple crop, manioc, and leaving the peel in the field, burning manioc to make charcoal, and spreading their decaying food scraps around the village.
All of this results in nutrient-rich, carbon-sequestering soil around the village, which the Kuiluro say is intentional. Intriguingly, the composition and positioning of the soil are very reminiscent of dark earth; however, additional future surveys will be required to confirm that dark earth is indeed human-made.
A Distant Origin
However, other research challenges the assertion that dark earth originates entirely from an ancient human presence in areas where it is found today. University of Oregon soil research Professor Lucas Silva conducted a 2021 study that found traces of plant material in the soil that were not native to rainforests but instead came from savannahs.
As his team continued to study dark earth, they discovered something novel: minerals that were not indigenous to the region. Based on this, Professor Silva suspects that rivers transported nutrients from further distant lands, allowing local people to harvest from the nutrient-rich riverbanks and use them in their agriculture.
According to Professor Silva, no one has been able to recreate the dark earth because they have not solved the mystery of its origin. Among the issues with recreating dark earth is that small elements, such as microbial content, play a significant role in the soil’s unique properties.
Dr. Santos de Freitas, who conducted the Brazilian experiment in which 20% of the mysterious soil was placed in a struggling area, has been working in his lab to understand and recreate the delicate microbial balance found in dark earth, each with its own essential role. The goal of that work is to eventually recreate a similar substance in the lab.
“I’m currently enrolled in a postdoc position aiming to isolate the microbial effect of (dark earth) ADE and test different approaches, Dr. Santos de Freitas told The Debrief. “One of them includes biochar to mimic part of the ADE’s chemical composition, but the study is in its beginning.”
While these attempts at reverse-engineering dark earth have yet to fully recreate the variety found in the Amazon, Dr. Santos de Freitas says the current work is a meaningful step in that direction.
“[I’m] not sure if we can call it dark earth, but considering we’ll have an ADE-like product in the future, we’ll have a broad-spectrum fertilizer with both chemical and microbial characteristics that improve plant growth,” Dr. Santos de Freitas told The Debrief, adding that “it could be used for either trees in ecological restoration or crops.”
“Our target is driven by sustainable development,” he said.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.
My hypothesis is that dark earths started from privy pits. People used charcoal from where they cooked a meal and dumped it in the pit to kill the smell. Once the pit filled they dug another. Eventually they found out that the former pits made great farm soil. The bacteria in the human microbiome bound those minerals onto organic molecules which then clung to charcoal instead of rinsing out of sandy soils.
Is this related to “Demetrius Earth”?
Good soil caused by build up of organic decomposing and plants like this???
Who knew 😎
1. LIDAR images show that thousands of years ago the Amazon had thousands more human settlements than it does today; that it once held a large population.
2. Many of the locations of the Amazonian “dark soil” correspond to where LIDAR (ground penetrating radar) images show outlines of ancient human settlement.
Graham Hancock takes the position that a very, very (during the last ice age) ancient civilization in the Amazon river basin created the black soil.
bottom land ping
article, #5
That seems likely as a factor. Slash and burn, leveling of the ground, continuing compost, new field every year in rotation, old field used for the outhouse, and circling ‘round for generations.
LIDAR and RADAR, are not the same thing.
Within the context of mapping the remains of ancient civilizans ...
LIght Detection And Ranging uses coherent visible or near infrared radiation to map the ground surface at very high precision. The Source is a LASER.
Ground Penetrating RADAR (RAdio Detection And Ranging) uses microwave radiation to map objects and structures under the ground surface which differ in absorption or reflection from the overall ground material.
They are similar and complementary technologies, not the same.
“...and are most often associated with the accumulation of materials in soil after long periods of human settlement.”
Human waste, food caches, burn pits or campfires is my guess, ending up as spots rich with Biochar.
“Biochar is a charcoal-like substance made from biomass through a process called pyrolysis, which involves heating organic material in a low-oxygen environment. It is primarily used as a soil amendment to improve soil health and sequester carbon.”
You can make your own, buy it, or let Mother Nature do it. ;)
I developed pretty good intuitions studying aboriginal peoples and their plantings in California, but I would dispute the ‘slash and burn,’ not in principle but by degree. With the Andes where they are, I suspect it’s always been rainy there. Hence they grew a “food forest” with multilayered production of trees, shrubs, and forbs. In that case (and based upon my experience with coppicing fruit bearing shrubs), I’m thinking it was a 3-5 year burn cycle with the “slash” coming thereafter as a matter of gathering firewood. How they might have confined their fires would be where the slashing comes in. Where I live, I suspect they used a particular groundcover plant for such burn boundaries (Gamochaeta ustulata). That stuff doesn’t burn worth a crap. Of course, the pattern of firewood gathering might accomplish much of the same thing, but groundcovers would be key anyway.
Look at that! I should have read down! R.B. already “garden” pinged you! (it was late.)
And every few years the building was replaced and the old building became firewood and flooring or just fell down and turned back into soil. If along a riverbank, they fished, and what did they do to the fins, heads, and tails (if they were not making soup that day!) Remember Tisquanto using fish fertilizer! (Biochar, fish byproduct, kitchen waste, and human waste in a riverside settlement.)
Lençóis Maranhenses, MA, Brasil. In Brazil, but not, I think, an amazonian indiginous tribal product. Makes the point, though, about generational concentrations of organic matter from indigenous Amazonian building materials.
I read all the way to the last comment, and nowhere did anyone mention the writings of a Spanish member of the conquest of the Inca who traveled down the Amazon to the Atlantic coast. He was quite impressed by the amount of civilization he found along the shores. No doubt he and his crew were generous in their distribution of new and deadly germs to the welcoming population which soon after ceased to exist.
Is it also possible that occasional volcanic eruptions sent burned waste and ash down the river which were collected and added to the shore soil?
I read all the way to the last comment, and nowhere did anyone mention the writings of a Spanish member of the conquest of the Inca who traveled down the Amazon to the Atlantic coast. He was quite impressed by the amount of civilization he found along the shores. No doubt he and his crew were generous in their distribution of new and deadly germs to the welcoming population which soon after ceased to exist.
Did a vehicle
Come from somewhere out there
Just to land in the Andes?
Was it round
And did it have
A motor
Or was it
Something
Different
Orellana’s account is a good suggestion. My guess is that tuberculosis and syphilis were the most deadly because of their long incubation periods. They would spread far and wide before people found out how sick they were.
From my readings, syphilis was brought to Europe by the explorers returning from America. I believe some called it the French disease. I suspect that the more common diseases like smallpox, measles and others did the most killing. I don’t know how quickly Orellana and crew arrived on the Amazon. Once there and exchanging germs, river traffic by the residents would have spread infections quickly up and down the Amazon and into tributaries.
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