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Friday, 3 February 2017

Africa as a continent

Africa is often called the cradle of humanity. It was in Africa that humans first arose long, long ago. From Africa, these people migrated into Asia, Europe, Australia, and the Americas.
Today, Africa is home to a remarkable variety of people and cultures. It is a land of striking contrasts and wild beauty. It is also a place facing many
problems, including war, starvation, poverty, and disease.


A VAST CONTINENT

Africa is the second largest of Earth’s seven continents, after Asia. It accounts for nearly one
-quarter of the world’s land. In the northeast, Africa touches Asia in Egypt. In the northwest, Africa almost touches Europe in Morocco. More than 50 nations are found in Africa. They are home to some 800 million people.

STRADDLING THE EQUATOR

Africa is the only continent that truly straddles the equator, the imaginary line that encircles Earth around its middle. Much of Africa is hot and dry. Only central Africa has a tropical rainy season. Yet few areas of the world are as diverse as Africa.
THE MIGHTY NILE
The longest river in the world, the Nile, empties into the Mediterranean in northeastern Africa. Ancient Egypt, one of the world’s first great civilizations, developed along the mighty Nile more than 5,000 years ago. Today, its magnificent pyramids still tower above the land.
THE SAHARA
The Sahara, the world’s largest desert, reaches across a vast swath of northern Africa. It stretches from the Atlantic Ocean in the west to the Red Sea in the east. In fact, the Sahara covers one-quarter of the entire continent. The Sahara is mainly hot, dry, and empty. But people have used teams of camels to carry goods across this giant desert since ancient times.
EQUATORIAL AFRICA
South of the Sahara is equatorial Africa, lying on either side of the equator. Here we find lush tropical rain forests and tropical grasslands called savannas. On Africa’s west coast are the trading ports of West Africa. These ports ship crops such as coffee, cotton, and cacao beans (from which chocolate is made) to the world.
The Congo River, Central Africa’s largest waterway, empties into the Atlantic Ocean near the equator. The Congo drains a vast basin in Central Africa that receives more rainfall than any other part of the continent. It carries more water than any river in the world except the Amazon River in South America.
GREAT RIFT VALLEY
The highlands of Africa are in the east. They run the length of the continent. Between mountain ranges lies the Great Rift Valley. It runs north to south for more than 3,000 miles (4,830 kilometers). The valley actually begins in the Asian country of Syria and reaches all the way to Mozambique in southeast Africa. The Great Rift Valley is rich with fossils. Here, scientists have found ancient bones that have helped them understand the mystery of human origins.
KILIMANJARO
Africa’s tallest mountains are found in the towering ranges of the east. Kilimanjaro, the highest mountain in Africa, rises in east central Africa. A dormant volcano, Kilimanjaro climbs to 19,341 feet (5,895 meters).
SOUTHERN AFRICA
In southern Africa is the great Namib Desert. This desert lines the southwest coast, reaching inland about 81 miles (130 kilometers). In the center is the fertile High Veld, a large plateau that slopes down to the Indian Ocean in the east. On the southern tip of the continent is South Africa’s famous Cape of Good Hope. This is the place where the Indian and Atlantic oceans meet.
MANY DIFFERENT PEOPLE
The people of Africa may be the most diverse of all the continents. Africa’s 800 million people speak perhaps 2,000 or more languages. Thousands of distinct ethnic groups are found in Africa.
North of the Sahara, people are mainly of Arab origin. South of the Sahara, the people are mostly black Africans. Throughout Africa are scattered people of European ancestry, descendants of colonial settlers.
Most Africans live in rural communities. Many raise livestock or farm. Relatively few people live in cities. But Africa does have many big cities, and they are growing rapidly. They include Cairo, Egypt; Casablanca, Morocco; Lagos, Nigeria; and Cape Town, South Africa.
From the 1500s to the 1800s, millions of Africans were forcibly removed to North and South America to work as slaves. Their descendants are still prominent among the people of both of those continents.
A WILD PLACE
Africa is famous for its stunning wildlife. The continent is home to thousands of species of mammals, birds, reptiles, amphibians, fishes, and insects.
South of the Sahara, Africa teems with animal life. Wild herds of antelope, zebras, giraffes, and impalas roam across the savanna. Lions, cheetahs, and leopards feed on them. Elephants live in some forests and grasslands. Gorillas live in the rain forests of Central Africa.
Today, many of these animals are endangered. Farms and cities have replaced much of the land they called home. They have been hunted for trophies, meat, and sport. Many countries in Africa try to protect endangered animals, but their numbers continue to dwindle.
MANY CHALLENGES
Today, Africa faces many challenges. The majority of its people remain poor. Droughts are frequent in many areas, leading to terrible starvation. Wars within and between countries have killed millions of people and forced millions of others to leave their homes and live elsewhere as refugees.
Diseases such as tuberculosis and malaria kill millions of Africans each year. In recent years, acquired immunodeficiency syndrome (AIDS) has spread rapidly, especially south of the Sahara. It has infected millions of people and devastated some regions.
Despite these troubles, Africa remains a magnificent place. Perhaps no other part of Earth is as varied in its geography, wildlife,
and people.
Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.





There is music in the air all around you. There are sounds of people talking in the air all around you. The sounds of music and talking are carried by radio waves. There are radio waves everywhere indoors and outdoors.
Radio waves are invisible. You cannot see or feel them. You can only hear radio waves if you turn on a radio. Radios turn radio waves into sound.
HOW DOES A RADIO WORK?
Radios need electricity in order to work. Your portable radio gets electricity from batteries. Your clock radio gets electricity from a cord that you plug into an electrical outlet in a wall.
Radios have a power switch or button that lets you turn the radio on or off. Radios have a volume control that lets you play the sounds loudly or softly. Radios also have a dial or button that lets you tune in your favorite radio stations. Each station has a special number on the dial. When you tune in a station, your radio turns radio waves from that station into sound.
Radios have a special wire called an antenna that can pick up radio waves in the air. Radios first turn the radio waves into electrical signals. Then they turn the electrical signals into the sounds of music, traffic and weather reports, or news about your hometown sports teams.
HOW DO RADIO WAVES GET INTO THE AIR?
A radio station sends electrical signals through wires to a tall tower called a broadcast antenna. Electrical signals get changed into radio waves at the antenna. The antenna sends the radio waves out in all directions.
Some radio stations broadcast on AM radio waves. Some programs are broadcast on FM waves. AM radio waves travel farther than FM waves, but FM waves make clearer sounds. Most radios can pick up both AM and FM radio waves.
TWO-WAY RADIO
Radio broadcasts only go one way, from the station to your radio. You can listen to radio, but you cannot talk back. Two-way radio lets people talk to each other on radio waves.
Police officers and firefighters use two-way radio. Firefighters at a big blaze can call for more help on their two-way radios. Soldiers use two-way radios on battlefields.
CELL PHONES AND WIRELESS COMPUTERS
Cell phones use radio waves. Your cell phone sends your phone calls on radio waves to an antenna. The antenna passes your call along. You can talk on a cell phone in a car, on a bus, or just when you are walking around.
Some computers hook up to the Internet with radio waves. These computers have special antennas that can find wireless “hot spots.” These computers do not need to be plugged into a telephone line to surf the Internet.
OTHER WAYS WE USE RADIO WAVES
The radar that lets airplanes and ships “see” things in fog or things far away uses radio waves. Radar systems send out radio waves. The radio waves bounce back from any large object they hit and make images on a radar screen.
Radio waves help us explore deep space. Radio telescopes listen for radio waves from far away in the universe. Astronauts in spacecraft talk to control centers on Earth using radio waves. Radio waves beam pictures to Earth from cameras on space probes visiting other planets.
Doctors use radio waves to see inside the body. They use radio waves from MRI machines to make pictures of people’s insides.
WHO INVENTED RADIO?
During the 1800s, several scientists made discoveries that led to the invention of radio. An Italian inventor named Guglielmo Marconi sent the first sounds on radio waves in 1895. The sounds he sent were just clicks. The clicks were a kind of code that carried telegraph messages. People already knew how to send telegraph messages over wires on land. Telegraph messages sent on radio waves helped ships at sea where there were no wires. Sinking ships could send messages calling for help.
Other inventors learned how to send music and voices over radio waves. Radio stations began broadcasting programs in the 1920s. Families used to gather around the radio to listen to band music, soap operas, or other radio programs.

Inventors have found more and more uses for radio waves. Radio waves have become very important for helping you stay in touch with family and friends.

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