|The Dry Places|
Deserts are the driest places in the world, with less than 25 cm ( 10 in ) of rain per year,
They cover about 14 percent of the land. In some deserts, there may be no rain for many years and then, during one great storm, large areas may be flooded.
Some deserts, such as the Sahara in Africa, are hot in the day but often cold at night. Other deserts, such as the Gobi in China and Mongolia, have bitterly cold winters.
The world's largest hot desert is the Sahara. It stretches across North Africa from the Atlantic Ocean to the Red Sea and covers about 9 million sq km ( over 3 million sq miles ). The highest air temperature, 58 degrees C (136.4 degrees F ), was recorded in Libya, in the Sahara.
Cave paintings from the central Sahara show that, about 10,000 years ago, the Sahara was much wetter than today. Grass covered most of the land. But the climate changed and, by 5,000 years ago, the region had become a desert.
The world's largest cold desert is the Antarctica Desert.
It is over 14 million sq km in size ( over 5 million sq miles).
Poles and Tundra Facts
The land in Antarctica and Greenland is covered by two great ice sheets which never melt. Their cold, windswept polar climate is the harshest in the world.
Around the ice-covered areas of the Arctic lies a region called the tundra. Here, the ice and snow melt during the short Summer. No trees grow in the Tundra itself, but it merges with the evergreen forests of North America and Siberia in the USSR. These northern forests consist of coniferous trees, such as fir, larch, pine and spruce, which can survive the bitterly cold winters.
The lowest known air temperature, -89.2 degrees C
( -128.6 degrees F ) was recorded at the Soviet Vostok research station in Antarctica in 1983. In parts of Antarctica, the ice is 4,800 m
( 15,748 ft ) thick.
In the Arctic, about 12,000 icebergs break away every year from the glaciers whch flow down to the sea from the Greeland ice cap.
In the Arctic, the Sun never sets in the Summer and it is daylight all the time. In Winter, the Sun never rises and the days are cold and dark.
The word tundra is Finnish and it means treeless plain.
Plants and Animals