Amazon rainforest

• 1. Introduction

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  The Amazon rainforest holds an estimated 390 billion individual trees, spread across about 16,000 species. It covers most of the Amazon basin in South America, a basin that spans 7 million square kilometers, of which 6 million are forest. One in ten known species on Earth lives here. More than 30 million people of 350 different ethnic groups call it home, divided among nine nations and 3,344 formally acknowledged indigenous territories. For a long time, scientists assumed this was empty wilderness, too poor in soil to feed many people. The truth turned out to be stranger. Beneath the canopy lie roads, bridges, plazas, and a dark engineered soil that may have been made by human hands. How did a forest once thought pristine become a place archaeologists now believe was shaped by people for thousands of years? And why do many now warn it stands at a tipping point, on the brink of becoming something other than a forest?

• 2. A Name From War

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  Francisco de Orellana gave the Amazon its name after a war he fought with the Tapuyas and other tribes. The women of the tribe fought alongside the men, as was their custom. Orellana drew the name Amazonas from the Amazons of Greek mythology, the warrior women described by Herodotus and Diodorus. In 1542, Orellana became the first European to travel the length of the Amazon River. Previous generations dismissed his accounts as exaggeration. The BBC's Unnatural Histories later presented evidence that he was correct. A complex civilization was flourishing along the river in the 1540s, with agriculture advanced enough to support prosperous and populous societies, before disease from Europe such as smallpox swept it away.

• 3. The Counterfeit Paradise

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  Betty Meggers argued that the Amazon could never hold many people, a claim laid out in her book Amazonia: Man and Culture in a Counterfeit Paradise. She set the ceiling at a population density of 0.2 people per square kilometer, the maximum she believed hunting alone could sustain without agriculture. Recent anthropological findings have turned this view on its head. The Upano Valley sites in present-day eastern Ecuador predate all known complex Amazonian societies. Some 5 million people may have lived in the region in AD 1500, split between dense coastal settlements such as Marajó and inland dwellers. One estimate, based on projections of food production, suggests more than 8 million people in 1492. The collapse that followed was steep. By 1900 the native indigenous population had fallen to 1 million, and by the early 1980s it was below 200,000.

• 4. Earth Made Black

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  Geoglyphs carved into the land, dating between AD 1 and 1250, began surfacing on deforested ground from the 1970s onward. Ondemar Dias is credited with first discovering them in 1977, and Alceu Ranzi furthered their discovery after flying over Acre. These earthworks point to Pre-Columbian civilizations far larger than once assumed. Terra preta, a dark fertile soil, is found over large areas of the forest and is now widely accepted as a product of indigenous soil management. This engineered earth allowed agriculture and silviculture in a previously hostile environment. It means large portions of the Amazon are probably the result of centuries of human management rather than nature alone. In 2003, Michael Heckenberger and colleagues from the University of Florida found the remains of large settlements in the region of the Xingu tribe. Among them were roads, bridges, and large plazas, evidence of forest gardening and human shaping stretching back at least 11,000 years.

• 5. Warlike And Peaceful

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  More than a third of Yanomamo males, on average, died from warfare, according to missionary accounts from the borderlands between Brazil and Venezuela, who described constant infighting. The Jivaroan group, including the Shuar, practised headhunting for trophies and headshrinking, and tribes of the Jivaro fought repeated wars with their neighbors. The Munduruku expanded along the Tapajos river and its tributaries and were feared by neighboring tribes, until they were pacified and subjugated by the Brazilians in the early 19th century. Large war parties of the Bororo, Kayapo, Munduruku, Guarani, and Tupi people carried out long-distance raids. Against this backdrop, the Xingu stood apart. Ethnographers have described them as a peaceful society, turning to violence only to defend themselves against warlike neighbors. In the early 20th century, thirty Amazon basin tribes were listed as peaceful and eighty-three as warlike. Later contact carried its own dangers. In 1961, British explorer Richard Mason was killed by an uncontacted tribe known as the Panara, and the Matses made their first permanent contact with the outside world in 1969.

• 6. How The Forest Came To Be

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  The rainforest likely formed during the Eocene era, between 56 million and 33.9 million years ago, after a global drop in tropical temperatures and the widening of the Atlantic Ocean brought a warm, moist climate to the basin. It has existed for at least 55 million years. During the mid-Eocene, the Purus Arch split the drainage basin down the middle of the continent. Water on the eastern side flowed toward the Atlantic, while water to the west ran toward the Pacific. As the Andes rose, a large basin formed and enclosed a lake, now known as the Solimoes Basin. Within the last 5 to 10 million years, that accumulating water broke through the Purus Arch and joined the easterly flow to the Atlantic. The forest's diet of nutrients arrives from far away. More than 56% of the dust fertilizing the Amazon comes from the Bodele depression in Northern Chad in the Sahara desert. NASA's CALIPSO satellite measured an average of 182 million tons of dust blown out of the Sahara each year, 15% of which falls over the basin, carrying 22 million tons of phosphorus that replaces what rain and floods wash away.

• 7. A Living Inventory

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  One in ten known species in the world lives here, the largest collection of living plants and animal species anywhere. The region holds about 2.5 million insect species, tens of thousands of plants, and some 2,000 birds and mammals. Scientists have classified at least 40,000 plant species, 2,200 fishes, 1,294 birds, 427 mammals, 428 amphibians, and 378 reptiles. One in five of all bird species and one in five of all fish species are found here. A 2001 study found that a quarter square kilometer of Ecuadorian rainforest supports more than 1,100 tree species. Each hectare contains around 1 billion invertebrates. Not all of its residents are gentle. The black caiman, jaguar, cougar, and anaconda rank among the largest predators, while electric eels can stun or kill, and piranha bite and injure humans. Poison dart frogs secrete lipophilic alkaloid toxins through their flesh. Vampire bats can spread rabies, and malaria, yellow fever, and dengue fever can all be contracted in the region.

• 8. The Tipping Point

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  In 2022, about 20% of the Amazon had already been deforested, and a further 6% was highly degraded. Research suggests that reaching roughly 20 to 25% would trigger a tipping point, flipping eastern, southern, and central Amazonia into degraded savannah over decades. Seventy percent of formerly forested land, and 91% of land deforested since 1970, has been used for livestock pasture. There were 72,843 fires in Brazil in 2019, with more than half within the Amazon, and August of that year brought a record number. Drought has compounded the danger. In 2005, parts of the basin saw the worst drought in a hundred years, and a typical year sees the Amazon absorb 1.5 gigatons of carbon dioxide, while 2005 instead released 5 gigatons and 2010 released 8 gigatons. In 2021 it was reported that the Amazon emitted more greenhouse gases than it absorbed for the first time. The often-repeated claim that it produces more than a quarter of the Earth's oxygen actually refers to oxygen turnover, and the net contribution of the ecosystem is approximately zero. Conservation has shown it can pull the other way. Due to the policies of Luiz Inacio Lula da Silva, deforestation in the Brazilian Amazon fell by around 50% in the first ten months of 2023 compared to the same period in 2022, even through one of the worst droughts on record.