Level 1 — Absolute Beginner

In the Amazon rainforest, the dirt is usually not very good for plants. But there is one kind of dirt that is very dark and very rich.

This dirt is called dark earth. In Portuguese, the name is terra preta. Plants grow much better in it.

Scientists used to think it was natural. But new studies show that ancient people made it on purpose. They mixed ash, charcoal and food waste into the soil.

The Indigenous Kuikuro people in Brazil still make dark earth today. The dirt holds a lot of carbon. This may help us fight climate change.

rainforest

a wet forest with many trees and animals

Amazon

a huge rainforest in South America

dirt

the brown material plants grow in; another word is soil

dark

with little light or with a deep color

rich

having a lot of something good

ash

the soft powder left after something burns

charcoal

a black material made from burned wood

climate

the usual weather of a place over a long time

Level 2 — Elementary

Most of the soil in the Amazon rainforest is thin and not very fertile. But scientists have long known about strange patches of very dark and very rich soil scattered across the forest. The local name for this soil is terra preta, which means 'dark earth' in Portuguese.

For years, researchers were not sure how this special soil formed. Some thought it was natural. Others thought ancient people might have made it. New studies, including one focused on the Xingu Indigenous Park in Brazil, show that pre-Columbian Amazonians clearly made it on purpose.

The Indigenous Kuikuro people still build dark earth today. They mix ash, charcoal, animal bones, manioc waste and food scraps into special fields. They call the fields by Kuikuro words like ilũbepe and eegepe. Trees grow up to six times taller in dark earth than in nearby ordinary soil.

The discovery also matters for climate science. Researchers estimate that more than nine million tonnes of extra carbon is locked away in dark earth in just one slice of the Amazon. If the technique could be used carefully in other places, it might help store carbon and improve poor farmland at the same time.

soil

the layer of natural material where plants grow

fertile

good for growing crops

patch

a small area different from what is around it

ancient

from very long ago

Indigenous

belonging to the original people of a place

manioc

a starchy root crop, also called cassava

tonne

a metric unit of weight equal to 1,000 kilograms

lock away

to hold or store something safely so it cannot escape

Level 3 — Intermediate

A multi-year collaboration between Brazilian and U.S. researchers has produced what climate scientists are calling one of the most important results in the field in recent memory: confirmation that pre-Columbian Amazonians deliberately created the dark, carbon-rich soils known as terra preta, and that Indigenous communities such as the Kuikuro of the Xingu Indigenous Park continue to make them today.

Terra preta — literally 'dark earth' in Portuguese — has been studied since the 1960s, but its origin was debated. Some researchers argued it formed naturally from millennia of slow waste accumulation; others suspected human intervention. The new analyses, drawing on soil chemistry, archaeological dating, ethnographic interviews and remote sensing, line up firmly on the human-engineered side. The Kuikuro spread ash, charcoal, cassava waste and animal residues across fields they call ilũbepe (literally 'what was ashes') and later harvest the resulting eegepe.

The numbers are extraordinary. Terra preta stores roughly 150 grams of carbon per kilogram of soil, compared with only 20 to 30 grams per kilogram in surrounding tropical soils. In a single 24,281-square-kilometer slice of the Xingu region, scientists estimate that even though terra preta occupies just 3 to 4 percent of the area, it locks away upwards of nine million tonnes of carbon. Trees in dark-earth patches grow up to six times taller than in adjacent ordinary soil, and a 2023 experiment showed that adding 20 percent terra preta to nearby degraded farmland doubled crop growth in a single season.

The climate implications could be substantial. If the technique can be transferred carefully — without overstating its applicability or appropriating Indigenous knowledge — terra preta points to a low-tech, high-impact pathway for storing carbon in soils while simultaneously rehabilitating depleted land. The authors stress that any deployment must center Indigenous partners and avoid the extractive patterns that have characterized so many earlier 'discoveries' in the Amazon.

pre-Columbian

from the time before Christopher Columbus arrived in the Americas

ethnographic

based on the careful, on-the-ground study of a people and their culture

remote sensing

gathering data about a place from satellites or aircraft

millennia

thousands of years

residue

what is left over after something is used or processed

deployment

the act of putting something into use

rehabilitate

to restore something to a healthy condition

appropriating

taking and using something that belongs to others without proper credit or consent

Level 4 — Advanced

A multidisciplinary collaboration spanning soil chemists at the University of Florida, the Brazilian agricultural research agency Embrapa, archaeologists at the Federal University of Pará, and Kuikuro Indigenous partners in the Xingu Indigenous Park has published the most rigorous evidence to date that the Amazon's celebrated terra preta is anthropogenic. The team integrates radiocarbon dating, organic-matter biomarkers, satellite-derived land-cover analysis and ethnographic fieldwork to argue that pre-Columbian Amazonians manufactured carbon-rich dark earth across substantial areas of the basin and that descendant communities are still doing so today.

The chemistry alone is striking. Terra preta typically stores around 150 grams of carbon per kilogram of soil — roughly five to seven times the level of adjacent tropical ferralsols — while also showing elevated phosphorus, calcium and stable charcoal-derived black carbon fractions. The black-carbon component is critical because it explains the soil's remarkable persistence: pyrogenic carbon resists microbial decomposition for centuries to millennia, anchoring the macronutrient cycle of the soil rather than venting back to the atmosphere as carbon dioxide.

Quantitatively, the team estimates that within a 24,281-square-kilometer sample area of the Xingu, terra preta covers only 3 to 4 percent of the surface yet stores upwards of nine million tonnes of additional carbon relative to surrounding soils. Aboveground productivity follows: dendrometric studies show trees on dark-earth patches reach heights up to six times those of conspecifics on neighboring oxisols, and a 2023 amendment trial in degraded fields doubled biomass when 20 percent terra preta was incorporated. The Kuikuro themselves operate the technology through structured deposition of ash, charcoal, cassava and animal residues in ilũbepe plots, later cultivated as eegepe.

Scientifically, the implications are sweeping and controversial. If the manufacture of terra preta can be ethically transferred, calibrated and scaled — a substantial 'if' that hinges on Indigenous partnership and not extractive replication — it offers a low-energy, biodegradation-resistant carbon sequestration vector that simultaneously rehabilitates degraded land. Skeptics caution that the agronomic conditions of the Amazon basin may not be reproducible elsewhere and that biochar amendments alone have a mixed empirical record. Either way, the work realigns terra preta from an ethnographic curiosity to a central exhibit in twenty-first-century climate-soil science, and raises the broader question of how much of the so-called 'pristine' Amazon is in fact the legacy of millennia of careful human management.

anthropogenic

originating in human activity

radiocarbon dating

a technique for finding the age of organic material from radioactive decay

biomarker

a measurable substance whose presence indicates a biological process