The Amazing Amazon

Discover Earth’s mightiest river and the rainforest wilderness that surrounds its banks

The Amazon is one of Earth’s two longest rivers. It stretches an incredible 6,800 kilometres (4,225 miles) west to east across South America – the approximate distance between New York and Rome. It’s also the world’s largest river by volume, transporting 20 per cent of the freshwater on Earth and more than the world’s seven next largest rivers combined.

Feeding this gigantic torrent is the rain and snow falling across around 40 per cent of South America. This area is called the Amazon’s drainage basin and is surrounded by three mountain ranges: the Andes to the west, Guiana Highlands to the south and Brazilian Highlands to the north. The Amazon Basin takes its name from the river. It is the world’s largest lowland with an area of between 6-7 million square kilometres (2.3-2.7 million square miles) – almost the size of Australia. At its widest, the basin stretches 2,780 kilometres (1,725 miles) from north to south.

Around 85 per cent of the Amazon Basin is filled with the Amazon rainforest, Earth’s biggest tropical forest. This densely vegetated region contains around half of the world’s remaining rainforest and is sometimes called the ‘lungs of the Earth’. An estimated 20 per cent of Earth’s oxygen is produced by the Amazon’s foliage, which draws in carbon dioxide and releases oxygen via mass-scale photosynthesis.

Rainforests form in the Amazon Basin because of its equatorial climate; it lies within 15 degrees of the equator. Conditions are warm and wet year-round with little difference in weather between seasons. Average temperatures are about 26 degrees Celsius (79 degrees Fahrenheit) and rain falls, on average, 250 days a year.

The steady tropical climate encourages varied fast-growing plants. In just one hectare (2.5 acres) of Amazon rainforest in Ecuador, scientists found an incredible 473 tree species. The tallest trees can reach heights of 46 metres (150 feet) and live for thousands of years. Their huge leafy canopies harvest perhaps 70 per cent of incoming light and 80 per cent of rainfall, preventing it reaching the forest floor. When a tree topples, saplings race

upwards to fill the space. Beneath these is a shrub layer and a second forest layer – 20 metres (65 feet) tall, the height of British deciduous trees. When the trees and shrubs die, rapid leaf decay releases nutrients that fuel the ecosystem.

The Amazon Basin teems with life. More than one in ten species live in the Amazon – many found nowhere else. These include around 20 per cent of Earth’s bird species, 370 reptile species, thousands of tree-dwellers, and 7,500 butterfly species compared to about 60 in the UK. Many more species remain undiscovered. An average three new plant and animal species were catalogued each day between 1999 and 2009, according to conservation group WWF. These included a four-metre (13-foot)-long snake, a bald-headed parrot and a blind crimson catfish.

The Amazon is threatened by deforestation and climate change. In the last 50 years or so, at least 17 per cent of the trees in this remote wilderness have been cleared. The rainforest is so huge that it produces around 50 per cent of its rainfall by releasing water from its leaves. Cut down enough trees and the remaining rainforest would dry out, and die of drought or forest fire.

Amazing Amazon Animals

Freshwater dolphin

These pink dolphins detect prey in the muddy river waters with echo-location. Necks twistable at right angles help them slither between flooded trees. Males sometimes twirl sticks to impress females.


A relation of elephants, these aquatic mammals can weigh a massive 600 kilograms (1,300 pounds), reach four metres (13 feet) long, and eat 15 per cent of their body weight in vegetation on a daily basis.

Red-bellied piranha

Piranha fish have sharp, tightly packed teeth for tearing meat. They pinpoint struggling or bleeding animals in the water by smell and with an organ that detects changes in water pressure.

Scarlet mascaw

Among the world’s largest parrots, they can measure almost one metre (three feet) from beak to tail and weigh more than a kilogram (2.2 pounds). Highly intelligent, some have lived for 75 years.

Boa constrictor

These snakes kill by crushing creatures in their coils before swallowing them. Up to a staggering four metres (14 feet) long, they can eat prey whole by dislocating their jaws.

Golden lion tamarin

These squirrel-sized monkeys are among Earth’s most endangered species with fewer than 1,500 left in the wild. Around 90 per cent of their habitat has been cut down.


Earth’s third-biggest cat after tigers and lions, jaguars can be 1.8 metres (six feet) long and weigh 550 kilograms (250 pounds). Once widespread, they’re now common only in remote regions like the Amazon.

Urania moth

These vivid, iridescent moths are active during the day – unlike the vast majority of moths – and live along rainforest riverbanks. They are migratory, often flying along the course of rivers.


The toucan’s bright-coloured bill can reach a huge 19 centimetres (7.5 inches) long – that’s 30 per cent of the bird’s body length! The beak is very light though because it’s honeycombed with air.

 This article was originally published in How It Works issue 33, written by Vivienne Raper 

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