The word ‘biochar’ might be new, but what it describes is definitely not. The use of charcoal to enrich the soil – and, as a result, plant and tree health – dates back millennia. It was first used in ancient settlements on the banks of the river Amazon, deep within the rainforest.

Surprisingly, the soils of tropical forests are extremely poor – acidic and low in minerals and nutrients. The luxuriant vegetation of the jungle exists because of something called ‘nutrient cycling’. This means that most of the carbon and essential nutrients of the rainforest are locked up in its vegetation. As this organic matter decays, it’s recycled so quickly that few nutrients ever reach the soils, leaving them practically sterile.

When they took up farming, the indigenous people got round this problem by engineering extremely potent soils using charcoal. These human-made super soils still cover up to 10% of the Amazon basin. Scientists have dated them back at least 2,500 years – some even as far back as 6,000 years. We are only beginning to understand how pivotal these soils were to life in ancient Amazonia. Using new techniques like remote sensing, contemporary archaeologists are uncovering more and more remains of large cities deep inside the rainforest. The population was obviously much bigger than previously thought. And there’s increasing evidence that it was biochar that made these complex Pre-Columbian civilisations possible – as it made the soil fertile enough to grow food for such large numbers of people.

Even in modern day Brazil this ‘terra preta do indio’ or ‘dark earth of the Indians’ is still sought after by local farmers, as it’s so good at reviving poor or over-farmed soils. Its exact recipe remains a secret, shrouded in the mists of time. There’s much evidence to suggest, though, that the original inhabitants of Amazonia also used dung, bones and plant waste to boost the soil. These amendments, however, are used the world over. The addition of biochar is what makes terra preta different.

After the European arrived in the fifteenth century and destroyed most indigenous Amazonian civilisations, through violence and the spread of disease, biochar was largely forgotten about. It was only in the 1960s that some Dutch scientists began to take an interest in it. When they discovered these areas of black, highly fertile soils in tropical forests – where soils are naturally poor and devoid of nutrition – it raised many intriguing questions. Slowly and surely a groundswell of academic interest in biochar began to build.

What really struck scientists about terra preta was its tenacity. Once carbon dating showed these soils to be thousands of years old, their ongoing potency seemed a wonder. But the answer lay in the charcoal. In normal soils the carbon from decayed vegetation is relatively unstable. For example, when a field is ploughed it gives off carbon dioxide. But the terra preta soils are different. The carbon in biochar has been mineralised, so it is very resistant to breaking down. This stability makes it possible to lock away carbon for a long time. In terms of climate change, this could be a game-changer. The widespread application of biochar to soil could be one way of dealing with the runaway carbon emissions that are overheating the planet.

Combined with biochar’s ability to boost soil health, its potential as a carbon sink means that scientific interest in biochar is now at an all-time high. Environmental icons like James Lovelock and Al Gore are advocating it as one way of restoring balance to our ecosystems. We at Sacred Earth also think that, in conjunction with other measures such as reforestation, it’s one of the best ways to restore soil health and cool our planet. And for this chance to regenerate our ecosystems, we have the ancient peoples of the Amazon to thank.