Deep in the heart of the Amazon rainforest lies a mysterious soil that has captivated scientists for decades. Known as “Amazonian dark earth” (ADE), or “black gold” or terra preta, this dark layer of earth can reach up to 3.8m (12.5ft) in thickness. It is not evenly distributed, but rather scattered in patches throughout the Amazon basin. What makes this soil so remarkable is its fertility – it contains abundant organic matter and nutrients that are vital for growing crops, such as nitrogen, potassium, and phosphorus. However, this soil is not a natural product of the rainforest ecosystem, which usually has thin, sandy soils. Rather, it is a legacy of ancient human activity.
You can also read: Microsoft Surpasses $3 Trillion Mark
This soil bears witness to a very different history of the Amazon – a time when indigenous peoples built flourishing settlements across this vast green landscape. In January 2024, a team of scientists revealed the stunning discovery of a “garden” city that had been hidden under the rainforest canopy for centuries. Located in Ecuador’s Upano Valley, this ancient urban center dates back to 2,000 years ago. It featured plazas, streets, and ceremonial platforms that indicated a complex social organization. This discovery sparked curiosity about the possibility of other lost cities in the Amazon. And this is where ADE plays a crucial role. It is believed that the garden city could sustain a large population because of the region’s fertile volcanic soil. However, in other parts of the Amazon, indigenous peoples used ADE to enhance the productivity of their land. Their methods of creating and managing this soil are now of great interest to modern societies, as they may offer solutions for increasing food security and combating climate change.
How was ADE created?
The origins of ADE are still debated by researchers, but most agree that it was created by people through a combination of intentional and accidental practices. One of the key ingredients of ADE is charcoal, which is produced by burning organic matter at low temperatures. Charcoal is stable and remains in the soil for thousands of years, binding and retaining minerals and nutrients. Charcoal also provides a habitat for beneficial microorganisms, which help decompose organic matter and release nutrients.
Indigenous Amazonians used charcoal for various purposes, such as cooking, heating, pottery making, and ritual activities. They also practiced slash-and-char agriculture, which involves clearing a patch of forest by cutting and burning the vegetation. This creates a layer of ash that fertilizes the soil for a short period of time before the nutrients are consumed or leached away by rain or flooding. This forces farmers to migrate to an unburned area and clear it. However, some researchers suggest that indigenous Amazonians also added charcoal and other organic materials, such as bones, shells, manure, and pottery fragments, to the soil to enhance its fertility and stability. This way, they could cultivate the same plot for longer periods of time, or even indefinitely.
Archaeological evidence shows that ADE was created by farming communities between 450 BCE and 950 CE and that it covers an estimated 6,000-18,000 square kilometers of the Amazon basin. Some studies suggest that ADE may actually cover more than 150,000 square kilometers or 3.2% of the total forest. ADE is often found near archaeological sites, such as mounds, plazas, roads, and canals, indicating that it was associated with complex societies that had large populations and sophisticated technologies.
What are the benefits of ADE?
ADE has many benefits for both the environment and human well-being. ADE is a highly productive soil that can support a variety of crops, such as maize, cassava, sweet potato, cacao, and fruits. Indigenous Amazonians have been using ADE for centuries to grow food, and some still do today. ADE also supports a higher diversity and biomass of plants than the surrounding forest, including edible species like Brazil nuts and acai palms. ADE also attracts wildlife, such as birds, mammals, and insects, which provide food and other resources for humans.
ADE is also a valuable carbon sink, meaning that it stores carbon that would otherwise be released into the atmosphere as greenhouse gases. ADE contains up to 70 times more carbon than the surrounding soils, and up to 10 times more than the average global soil. ADE also reduces carbon emissions by preventing deforestation and forest degradation, which are major sources of greenhouse gases. By enhancing soil fertility and stability, ADE reduces the need for clearing new land for agriculture and allows for the regeneration of forests on degraded land.
ADE also has cultural and historical significance, as it represents the legacy of indigenous Amazonians and their interactions with the environment. ADE is a living archive of human history, as it contains artifacts, such as pottery, stone tools, and fossilized seeds, that reveal information about the past societies that created and used it. ADE also reflects the knowledge and skills of indigenous Amazonians, who developed sustainable and resilient ways of managing the land. ADE is a source of pride and identity for many indigenous communities, who consider it a sacred and ancestral soil.
What are the challenges of ADE?
Despite its many benefits, ADE also faces several challenges that threaten its existence and use. One of the main challenges is the lack of recognition and protection of ADE by governments and other actors. ADE is often ignored or undervalued in land use planning and decision-making and is vulnerable to land grabbing, mining, logging, and other destructive activities. ADE is also often appropriated or exploited by outsiders, who do not respect the rights and interests of indigenous communities. ADE is also subject to erosion, contamination, and degradation, due to climate change, pollution, and poor management practices.
Another challenge is the loss of traditional knowledge and practices related to ADE. Many indigenous communities have been displaced, assimilated, or exterminated by colonization, disease, and violence, and their cultures and languages have been suppressed or erased. As a result, much of the knowledge and skills of creating and using ADE have been forgotten or abandoned. Many indigenous communities also face discrimination, poverty, and marginalization, and have limited access to education, health, and other services. These factors affect their ability and willingness to maintain and transmit their traditional knowledge and practices to future generations.
A third challenge is the lack of research and innovation on ADE. ADE is still a relatively understudied and misunderstood phenomenon, and there are many gaps and uncertainties in the scientific knowledge about its origin, distribution, properties, and functions. There is also a need for more interdisciplinary and participatory research that involves indigenous communities and other stakeholders, and that respects their knowledge, values, and perspectives. There is also a need for more research and development on how to replicate, restore, and enhance ADE, and how to apply its principles and practices to other contexts and scales.
How can we preserve and promote ADE?
ADE is a precious and unique resource that has the potential to contribute to the conservation and restoration of the Amazon rainforest, as well as to the food security and well-being of its inhabitants. However, to realize this potential, ADE needs to be preserved and promoted through various actions and strategies. Some of these actions and strategies are:
- Recognizing and protecting the rights and interests of indigenous communities over ADE, and ensuring their participation and consent in any decisions or interventions that affect ADE.
- Raising awareness and appreciation of the value and importance of ADE among governments, policymakers, researchers, civil society, and the general public, and advocating for its inclusion and integration in land use planning and decision-making.
- Supporting and strengthening the traditional knowledge and practices of indigenous communities related to ADE, and facilitating their transmission and exchange among generations and groups.
- Conducting more research and innovation on ADE, using interdisciplinary and participatory approaches, and generating and disseminating relevant and accessible information and knowledge for different audiences and purposes.
- Developing and implementing best practices and guidelines for the creation, restoration, and enhancement of ADE, and for its sustainable and equitable use and management.
- Establishing and expanding networks and partnerships among different actors and sectors, such as indigenous communities, researchers, NGOs, governments, and the private sector, to share experiences, resources, and solutions related to ADE.
By taking these actions and strategies, we can ensure that ADE is not only a relic from the past but also a resource for the present and the future.
