A biome is a huge area of Earth where the weather, the plants and the animals are all alike. The main land biomes are the tropical rainforest, the savanna, the desert, the grassland, the temperate forest, the taiga and the tundra, and the biggest biome of all is the ocean, which covers about 71 percent of the planet. Two things decide which biome a place gets: how warm it is and how much rain falls there. So a hot, wet place like Manaus in Brazil, with about 2,300 mm of rain a year, grows rainforest. A hot, dry place like the Sahara, where most ground gets less than 20 mm a year, becomes desert. Below, each biome is tied to one real place, with its weather and two of the living things you would meet there.
Scientists measure rain in millimetres (mm). Imagine putting a straight-sided bucket outside for a whole year and never emptying it. If the water ends up 1,000 mm deep, that place gets 1,000 mm of rain a year. That is one whole metre, as long as a metre stick! Temperatures in this article are in degrees Celsius (°C). Water freezes at 0 °C.
Tropical rainforest: the Amazon near Manaus, Brazil
The Amazon rainforest is the largest rainforest on Earth. It covers about 6 million square kilometres of South America, and most of it is in Brazil. The city of Manaus sits right in the middle of it.
In Manaus the average temperature is 27.4 °C. That is like a warm summer day, every day of the year. It rains about 2,300 mm a year. Even the driest month is only just a little dry.
Heat plus rain makes plants grow fast. Scientists think the Amazon has about 390 billion trees of around 16,000 kinds. One in every ten kinds of living thing that scientists know about lives here. The trees grow so close that their tops join into a roof of leaves called the canopy.
Two animals to look for are the jaguar, a big spotted cat that is one of the forest's top hunters, and the poison dart frog, a tiny bright frog whose skin is poisonous so that other animals leave it alone. Find out more in our rainforests for kids page.
Savanna: the Serengeti in Tanzania
A savanna is a warm grassland with trees dotted here and there. The trees are spread out because there is not quite enough rain for a full forest. Most savannas have a wet season and a long dry season, and dry grass often catches fire.
The Serengeti is in Tanzania, in East Africa, and stretches into Kenya. It gets between 508 mm and 1,200 mm of rain a year. The driest parts are near the Ngorongoro highlands, and the wettest are by Lake Victoria.
The flat-topped tree you see in many pictures of Africa is the acacia. In the Serengeti, acacias have spread again since the 1970s, because big herds now eat so much grass that fires burn less fiercely.
The Serengeti's most famous animal is the blue wildebeest, a kind of antelope. Every year more than 1.5 million wildebeest walk in a giant loop, following the rain to find fresh grass. It is one of the biggest animal journeys on Earth. Following them is the lion. The Serengeti National Park has the largest lion population in Africa.
Desert: the Sahara in North Africa
A desert is a place that gets very little rain. It is not always hot, but the Sahara certainly is. It is the largest hot desert in the world, covering about 9 million square kilometres. That is nearly a third of Africa.
Most of the Sahara gets less than 20 mm of rain a year. In the very middle, the average for a whole year can be less than 1 mm, which is thinner than a coin. In the hottest month, the average afternoon temperature is above 38 °C almost everywhere. The sand can heat up to 80 °C, hot enough to burn your feet. But with no clouds to hold in the heat, nights are 13 to 20 degrees cooler than the days.
Animals here have clever tricks. The fennec fox is a small fox with enormous ears that let heat escape from its body. The addax, a white antelope, can go nearly a year without drinking. It gets water from its food and from dew on plants. People who cross the desert ride the dromedary, the camel with one hump. Our deserts for kids page visits more of the world's deserts.
Grassland: the tallgrass prairie of Kansas
A grassland is a wide, open land covered mostly in grass, with few trees. In North America these grasslands are called prairies. Most have been ploughed into farms. The biggest piece of tallgrass prairie that has never been ploughed is in the Flint Hills of Kansas, in the middle of the United States.
At the Konza Prairie, a protected area in the Flint Hills, about 835 mm of rain falls each year. Summers are warm and wet, and winters are cold and dry. That is actually enough rain for trees to grow. So why is it still grassland? Fires, dry spells and grazing animals stop trees from taking over.
The grass can grow taller than a grown-up, reaching more than 2.5 metres in good years. One of the main grasses is big bluestem. Its seed head splits into three parts like a bird's toes, so people also call it turkeyfoot. The biggest animal of the prairie is the American bison, which can weigh more than a small car. Millions once grazed here before hunters nearly wiped them out. Today herds have been brought back to protected prairies.
Temperate forest: the Great Smoky Mountains, USA
"Temperate" means not too hot and not too cold. Temperate forests have four clear seasons. Many of their trees are deciduous, which means they drop their leaves in autumn and grow new ones in spring.
The Great Smoky Mountains National Park lies on the border of Tennessee and North Carolina. It gets between 1,300 mm and 2,000 mm of rain a year, with heavy snow on the highest peaks in winter.
The park is full of broadleaf trees. One is the tulip tree, named for its flowers, which look like tulips. Another is the sugar maple, whose leaves turn bright orange and red in autumn.
The animal the park is best known for is the American black bear. More black bears live close together here than anywhere else east of the Mississippi River. Most adults weigh between 45 kg and 140 kg.
Taiga: the larch forests around Yakutsk, Siberia
The taiga, also called the boreal forest, is the largest land biome on Earth. It wraps around the top of the world through Canada, Alaska, Scandinavia and Russia. Its trees are mostly conifers, trees with needles and cones.
Yakutsk, a city in eastern Siberia, Russia, is surrounded by taiga. It is the coldest city of its size on Earth. In January the average temperature is −36.9 °C. Yet in July it averages +19.9 °C. The coldest temperature ever measured there was −64.4 °C. The ground under the city is permafrost, soil that stays frozen all year, so many houses stand on concrete legs called piles.
The main tree here is the larch. Unlike most conifers, it drops its needles every autumn. The eastern Siberian taiga is one enormous larch forest. A big animal of the taiga is the moose, the largest member of the deer family. Hunting in the same forests is the Eurasian lynx, a wild cat with a short tail, big padded paws for walking on snow and black tufts on the tips of its ears.
Tundra: Utqiaġvik on Alaska’s Arctic coast
North of the taiga, it gets too cold and windy for trees. This treeless land is the tundra. Only a thin top layer of soil thaws in summer. Underneath is permafrost.
Utqiaġvik is the northernmost town in the United States. It lies 530 km north of the Arctic Circle. Temperatures usually stay below freezing from early October to late May. Less than 150 mm of rain and melted snow falls in a year. That is as dry as many deserts! In winter the sun sets on 18 November and does not rise again until 23 January. That means about 66 days of darkness.
Tundra plants stay low to hide from the wind. They include mosses and lichens, which are a partnership between a fungus and a tiny green life form called an alga.
Two tundra animals are the Arctic fox, which sheds its fur twice a year: its short summer coat is darker, and its long winter coat is lighter, often pure white, and the caribou, the North American name for the reindeer, which travels in big herds to find food.
Ocean: the Great Barrier Reef, Australia
The ocean is the biggest biome by far. It covers about 71 percent of Earth's surface and holds 97 percent of all Earth's water. It has its own zones, from sunny shallow water to the pitch-black deep sea. One of its richest places is a coral reef.
The Great Barrier Reef lies in the Coral Sea, off the coast of Queensland in Australia. It is the largest coral reef system in the world. It is made of more than 2,900 separate reefs and 900 islands, stretching over 2,300 kilometres. It was built by billions of tiny animals called coral polyps, which make hard skeletons that pile up over thousands of years.
More than 1,500 kinds of fish live on the reef. One is the clownfish, the orange-and-white fish that hides among the stinging arms of sea anemones. Six kinds of sea turtle visit the reef to breed, including the green sea turtle, which eats seagrass. Sadly, warmer seas are causing coral bleaching, when corals turn white and can die. Studies have found the reef lost more than half its coral cover between 1995 and 2017. Dive into more sea facts in our oceans for kids guide.
Now you can see the pattern. Warm and wet makes rainforest. Warm with a dry season makes savanna. Too dry for almost anything makes desert. Cold makes taiga, and colder still makes tundra. If you want to learn why the world is split into hot, mild and cold bands in the first place, take a look at our guide to climate zones for kids.