My Science School

South America is a continent of extremes. The world’s longest mountain range, the Andes, stretches along the west coast. Between the snow-capped mountains lies a high, cold and windswept plain called the altiplano. Between the Andes and the Pacific Ocean coast is the Atacama Desert, the driest place on earth. Rain may not fall here for hundreds of years at a time.

In the north, most people live near the Caribbean coast or in the mountains. Further inland, the vast rainforests of the Amazon basin dominate. The Amazon River originates in the Andes and winds its way eastwards through Peru and Brazil before reaching the Atlantic Ocean.

To the east of the Amazon rainforest lie the Brazilian Highlands. Further south are wide areas of fertile grasslands, known as pampas, which cover parts of Argentina and Uruguay. In the extreme south of Argentina, grasslands give way to the dry, bleak scrublands of Patagonia. The southern Andes is an region of glaciers and volcanoes, breaking up into bleak, rocky islands at its tip.

Many people in South America are descended from Europeans, especially the Spanish and Portuguese, who began to arrive during the 15th century. Most South American people today still speak these languages. Others are descendents of African slaves brought over by the Europeans. The numbers of native peoples of South America fell dramatically after the arrival of the Europeans, but some still live in the mountains and the rainforest, keeping their own languages and traditions.

AMAZON RAINFOREST

The Amazon basin is the largest area of rainforest in the world. Many kinds of plants and animals live there, and new species are constantly being discovered. The mighty Amazon River and its tributaries flow through the forest, providing a vital transport route and source of food for the native peoples who live in forest villages. A few of these peoples still follow a traditional way of life, hunting, fishing and growing crops. Many also take advantage of modern technology, such as engines for their boats.

Today, the rainforest is disappearing at an alarming rate, because of logging for the timber industry, road-building, and clearing space for cattle farming or crop planting. The poor-quality rainforest soil means that it cannot support grazing or crops for long before the farmers must move on to new areas. So even more of the forest is lost.

Mexico and the countries that make up Central America form a link between North and South America. Mexico is a mountainous country, with desert in the north, tropical forest in the south and a central plateau of fertile land. Its cities suffer from overcrowding and pollution.

Central America is a mainly agricultural area. Bananas and coffee are grown, and cattle are raised. There is a constant threat of volcanoes, earthquakes and hurricanes.

The first European settlers of this region were Spanish. They controlled the land for hundreds of years. Most Mexicans and Central Americans speak Spanish today.

CARIBBEAN ISLANDS

The beautiful islands of the Caribbean are popular tourist resorts. They also export crops such as sugar, bananas and coffee. Volcanic eruptions and frequent hurricanes are a constant threat to the islanders. Many Caribbean people are descended from black African slaves. Their cultures are a mixture of African and European traditions.

Although larger in size than the USA, Canada has a much smaller population than its neighbour. Most of the country is covered with vast coniferous forests, mountains and lakes, where bears, wolves, cougars and moose are abundant. In the far north, and on the Arctic islands, the ground is permanently frozen. On this barren land, known as the tundra, plants grow only in the short summer.

Some native peoples, including the Inuit, live in the icy northern territories, but most Canadians live in the south, near the border with the USA. The largest cities are located in the east. Further west, in the provinces of Alberta, Saskatchewan and Manitoba, lies a wide expanse of fertile, low-lying land known as the Great Plains, or prairies, where most of Canada’s wheat crop is grown. The western part of Canada is dominated by mountain ranges, including the Rocky Mountains, which stretch on south across the USA.

In the 16th century, the first European settlers arrived in Canada from both France and Great Britain. French and English are still the official languages spoken today. Most French-speaking Canadians live in the province of Quebec, and many wish to see it declared a separate country.

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The United States of America stretches from the Atlantic Ocean in the east to the Pacific Ocean in the west. Numbered among its 50 states are Alaska, which lies to the northwest of Canada, and the Pacific islands of Hawaii.

Running down the northeastern side of the USA are the densely-forested Appalachian Mountains. To their northwest lie the Great Lakes, vast inland seas that were gouged out by glaciers during the Ice Ages and filled by their melt-waters. To the east lie the coastal lowlands, where great cities such as New York, Boston and Washington have grown up.

Covering the central belt of the USA is a vast, flat area of farmland. In the northern part, crops such as wheat and maize are grown, while cotton, tobacco and nuts are cultivated further south. The vast Mississippi River cuts through several of the Midwestern states, dividing the USA in two.

West of the high Rocky Mountains, the climate is drier, and the landscape more rugged. Wide areas of hot desert stretch across the southwestern states of Nevada and Arizona. Near the west coast, the climate becomes milder. Rich farmland nestles among the mountain ranges of California and the northwestern states.

Before the first settlers arrived from Europe, the Native Americans were the only inhabitants of the USA. Today, Americans can trace their ancestors from all parts of the world. Many black Americans are the descendents of slaves brought over from Africa in the 17th and 18th centuries.

North America includes Canada, the United States of America, Mexico, Central America and the Caribbean islands, as well as the largest island in the world, Greenland. In the sparsely populated north, the thick Arctic ice gives way to the barren tundra of northern Canada. The Rocky Mountains run down from Alaska to Mexico, while the forested Appalachians dominate the eastern USA. In the fertile lowlands of the Mississippi basin and the eastern seaboard, farms produce huge amounts of crops such as maize and wheat. Further south are the hot, dry deserts of southwestern USA and Mexico.

            Most people in North America are descendants of settlers from other parts of the world, the first of whom, the Europeans, arrived in the 16th century. Many Native American peoples lost their lands and their lives to the new arrivals. Today, the small groups of Native Americans that remain have their own territories. Many, especially the Inuit of northern Canada, still follow a traditional way of life.

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People have made many changes to the world they live in and some of these have had harmful consequences. As the world population increases, there is more need for bigger cities, new towns and farming land. Land has to be cleared, destroying the habitats of many animals and plants. Some of these are now extinct and others are in danger of becoming so. Hunting has also put animals in danger.

There is now nearly three times as much desert in the world as there was 100 years ago. This is partly due to farmers over-grazing their animals on the meagre grass and shrubs and to the clearance of woodland trees for firewood.

Industrialization is a major threat to the environment. Pollution is just one example. Factories discharge harmful chemicals into rivers and seas, killing fish and plants.

The production of chlorofluorocarbons (CFCs) is reckoned to be responsible for damaging the ozone layer, the protective layer in the Earth's atmosphere that prevents harmful rays from the Sun reaching the surface. CFCs are synthetic chemicals used in aerosol sprays and refrigerators. When they are released into the atmosphere, they destroy the ozone. There is now a hole in the ozone layer above Antarctica.

Air pollution is caused by fumes and smoke from vehicles, factory chimneys and power stations. Poisonous gases, such as sulphur dioxide, mix with rain and mist to produce acids. When the acid rain falls, it kills plants over a wide area. Burning fuels also causes a build-up of carbon dioxide.

Carbon dioxide and CFCs are both greenhouse gases. In the right amounts, greenhouse gases in the atmosphere trap heat from the Sun so the Earth is not too hot or too cold. But if the greenhouse gases build up, too much heat is trapped and the Earth becomes warmer. This change in climate, known as global warming, could have disastrous effects. The ice in the Polar Regions may melt, causing severe flooding to low-lying areas. Changes in the climatic pattern worldwide could lead to violent storms and long droughts.

Some nations in the world are rich, while others are very poor. The gap between them seems to grow ever wider. Measured by the average income earned by people in the richest and poorest fifth of the world's nations, the gap has grown from 30 to 1 in 1960 to nearly 80 to 1 today. Within both rich and poor countries, there are also great contrasts in wealth.

The wealthiest countries are those that have developed industries and services which can supply their own populations with all their needs. They do this either by producing these products and services themselves, or by importing them from other countries, paying for them by exporting goods. In poorer developing countries, people may produce only enough food to feed their families. Disease and climatic disaster may prevent even this.

The population of developing nations has grown greatly in recent years. Their high birth rates means even more mouths to feed.

South America has some of the fastest-growing cities in the world. They include the Brazilian super cities of Sao Paulo and Rio de Janeiro, both with populations of more than 10 million. People from the countryside flock to these cities to find work but there is nowhere for them to live. They build their own shantytowns (locally known as favelas) just outside the city by building shelters and shacks from any material that comes to hand. People who live in shantytowns cannot find work easily and so they are forced to work for very low wages.

The wealth of a nation can be measured by its gross domestic product (GDP).This is defined as the value of all the goods and services produced there, including those produced by foreign-owned firms. The Group of Seven (G7) are the seven leading industrial nations of the world. These nations - the United States, Japan, Germany, France, the United Kingdom, Italy and Canada - account for more than 60% of the world's GDP. The country with the highest GDP per person in 1996 was Switzerland ($46,000). In the same year, the figure for Rwanda in Africa was $100. More than 1.3 billion people around the world live on less than one dollar a day.

Wealthy nations such as the G7 lend money to developing countries. However, the developing countries often find that, because of their low GDP, they cannot repay the loans and a big debt burden builds up. The largest foreign aid donor in 1996 was Japan with aid amounting to more than $15,000 million.

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Bridges have been used since ancient times to span deep ravines, rivers and other stretches of water. Early bridges were made of wood which rotted easily and could not span great distances. In some parts of the world, people made bridges from wood and rope. They had walkways made of wooden slats and rope handrails. Bridges made of stone may last for centuries. However, stone is heavy to transport and long bridges need to have many sturdy supports.

During the Industrial Revolution, which began in the 18th century, engineers began to build bridges made from iron. These were much more durable than wooden bridges and could span longer distances than stone ones. The first iron bridge was built at Coalbrookdale, England, in 1779.

Modern bridges are built using steel and concrete. They may carry roads or railways over rivers, wide estuaries or high valleys, or above other roads and railways. There are a number of different kinds of bridge design available, each of which may be used in a modern bridge according to the type of crossing required.

A beam bridge is one of the simplest and oldest designs. The beam is supported at each end. The earliest bridges were tree trunks or stone slabs laid across a stream supported by the banks on either side. A clapper bridge is a type of Beam Bridge which is supported from beneath by several columns in the river bed or ground. The deck may be flat or made from a hollow girder (truss) containing the road or railway.

An arch bridge—a very strong type—has a deck supported on an arch fixed to the banks. Some arch bridges are too low for river traffic to pass underneath so a part of their span may be a bascule or lift bridge.

This can be raised in the middle like a drawbridge so that ships can pass through.

A cantilever is a beam or structure that is fixed at one end only. Cantilever bridges are built in two halves, with each beam cantilevered out from the bank and each half balanced on a support in the river. There may be a short central span where the two halves meet.

Suspension bridges can span long distances. The towers of the bridge are built first and long steel cables are suspended from the towers. Lengths of cable called hangers are fixed to the suspending cables. The deck of the bridge is lifted into position and attached to the hangers. Suspension bridges are ideal for long, high spans as they do not require a row of supporting columns that may interfere with river transport. One of the most famous examples of a suspension bridge is the Golden Gate Bridge (1280 metres), near San Francisco in the USA, which was completed in 1937.

A cable-stayed bridge has diagonal steel cables running from high supporting masts at either end connected to the deck of the bridge. The weight of the deck is supported by the masts.

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Skyscrapers are very tall buildings, usually more than 20 storeys high. Their weight is supported by a steel frame rather than outside walls. They are a feature of many large cities, especially in North America and East Asia, where the high price of land leads developers to build tall, thin buildings that occupy the minimum amount of land space, rather than low-rise, sprawling ones.

The first skyscraper, the Home Insurance Building, was built in Chicago in 1884 following a fire that devastated the city. Soon, skyscrapers started to appear in New York as well as Chicago, often being built higher and higher in competition with one another. In recent years, Japan, Malaysia and China are among nations that have joined the race to build the world's tallest buildings.

The John Hancock Center in Chicago, USA, was completed in 1968. A skyscraper with both offices and residential apartments; it is the tallest multi-purpose building in the world and the seventh tallest skyscraper of all. It is 344 metres high but its twin antennae add a further 105 metres, making it a total of nearly 450 metres. It has a hull and core construction—a strong central concrete core with an open space between it and the steel frame. The frame has a triangular grid to give the structure maximum strength.

The John Hancock Center is like a city in a tower. It has shops, a bank, a post office, a restaurant, a swimming pool and a fitness centre. There are 50 lifts (it takes only 39 seconds to ascend to the 94th floor). A car park with spaces for 1200 cars takes up the first seven floors. Cars drive up a spiral ramp to get to it.

The building has more than 2000 kilometres of electric wiring, carrying enough electricity to supply the equivalent of a city of 30,000 people. More than 2.75 million litres of water are consumed each day. Computers warn of any fault in the skyscraper's service systems.

People have constructed buildings from ancient times as homes to provide shelter, monuments or places of worship. Earth, wood and stone have always been used as building materials. Bricks, hardened clay, were first used in the Middle East in about 3000 BC. Concrete is made by mixing sand, cement and water. Reinforced concrete dates from the late 1800s. Often used in modern buildings, it contains steel wires or rods to provide extra strength.

Buildings belong to one of two types. The first type has solid walls, called load-bearing walls that support the floors and roof of the building. The second type has a framework of wood, steel or concrete that bears the weight of the building.

Most buildings need foundations (a solid base) to prevent them from sinking into the ground or falling over. Foundations can be footings (underground walls), flat rafts, or underground supporting pillars called piles that are driven into the ground.

TALL STRUCTURES

The Great Pyramid at Giza in Egypt was the world's tallest structure for nearly 4000 years, until the great age of cathedral building began in medieval Europe. Lincoln Cathedral in England, which was built in 1311, had a great spire that made it slightly taller than the pyramid, although it was blown down in a storm in 1549. The Washington Monument in Washington, USA, became the world's tallest structure in 1884, before the Eiffel Tower in Paris, France, almost doubled the record five years later. The skyscrapers of the 20th century claimed the honour until the CN Tower, still the world's tallest self-supporting structure, was built in Toronto in 1976.

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Even though aircraft now carry many of the world's passengers, shipping is still a vital link between countries, particularly for carrying cargo. The biggest vessels are called bulk carriers. They include oil supertankers, some of which are more than 450 metres long. Container ships carry general cargo stored in large steel boxes stacked up like building blocks. These can be unloaded directly on to trucks.

The River Rhine rises in Switzerland and runs along the border between France and Germany, then on through Germany and the Netherlands, meeting the North Sea near Rotterdam. It is one of Europe's most important industrial waterways. As well as barges carrying cargo, river boats take tourists along the river to see the vineyards and ancient castles on its banks.

Ships cross the oceans on fixed routes called shipping lanes. The world's busiest shipping lanes link Europe and North America with the Middle East and East Asia. Ships go through the Suez and Panama Canals to shorten their journeys, although supertankers, being too large for the Suez Canal, still travel around the southern tip of Africa.

Modern cargo ships are much larger than vessels of the past, and big, efficient ports with docks (enclosed areas of water) are needed so that their cargoes can be loaded and unloaded as quickly as possible. Some ships take cargoes inland along large rivers and man-made waterways called canals.

Two major canals, cut through narrow necks of land, provide much shorter routes between ports. They are the 165-kilometre Suez Canal in Egypt, linking the Mediterranean Sea with the Red Sea, and the 82-kilometre Panama Canal, connecting the Atlantic and Pacific Oceans.

Canals often link natural waterways and provide a transport route across a continent. The Main-Danube Canal, for example, allows the movement of goods between Eastern and Western Europe. The United States and Canada have more than 41,000 kilometres of waterways linked to the St. Lawrence and Mississippi rivers and their tributaries. The St. Lawrence Seaway connects the Great Lakes, and the cities of Chicago, Detroit, Cleveland and Toronto among others, with the Atlantic Ocean.

Cargo on inland waterways in industrial countries, for example, the River Rhine in Germany, is usually carried by barges which are towed by tugs. Sometimes several barges are strapped together. Barges carry cargoes along the Rhine to and from the port of Rotterdam in the Netherlands, the world's busiest port. Antwerp in Belgium is the largest inland port in the world. Even though it is 89 kilometres from the open sea, ships of all types load and unload cargoes there.

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Air travel has grown enormously since World War II. Until then, only the wealthy travelled by air. The development of the jet airliner in the 1950s made it possible for everyone to fly to destinations across the world.

The world’s busiest airport is O’Hare International near Chicago in the United States, with an average of one take-off or landing every 35 seconds and nearly 70 million passengers a year. Many of these flights are for people travelling within the United States - about 85 per cent of people travelling within the United States go by air. London’s Heathrow Airport handles more international traffic than any other airport with more than 55 million international passengers a year.

A large modern airport employs thousands of people. Air traffic controllers work in a control tower, directing all aircraft to and from runways and deciding when it is safe to take off or land. They have powerful radar equipment to keep watch over the whole airspace around the airport.

Baggage handlers load and unload suitcases from the aircraft. Once passengers have disembarked, ground crew prepares the aircraft to fly out again, and refuel it while firefighters stand by.

In the terminal, the passengers collect their baggage and go through customs, where officials check that they are not carrying drugs or goods which require import or export tax to be paid.

Airports also handle goods (air freight) that are required to be transported quickly. Warehouses store goods before loading and after arrival, when they are inspected by customs officials.

Security officers use X-ray equipment to check passengers for bombs, guns and other weapons. International passengers also have to pass through immigration where they show their passports and any visas that are required to enter the country. Officials often stamp the passport to show that passengers are entering the country legally. Airports also have lounges and restaurants where passengers can wait for their flights.

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Electricity is a type of energy that gives us heat and light and drives machines. To be useful, electricity must be made to flow in a current. In 1831 the British scientist Michael Faraday used a magnet to produce electricity. He moved a loop of wire over the magnet, causing an electric current to flow through the wire. This principle is used to generate electricity in power stations today. In thermal power stations, coal, oil or gas are burned to boil water, producing steam to drive a generator.

The steam from the boiling water rushes through pipes and turns a bladed wheel called a turbine. The turbine is connected to the generator, which consists of a huge magnet surrounded by copper wire. The turbine makes the magnet spin, thus producing an electric current in the wire.

The water can be heated by other means. The mineral uranium is the fuel used in a nuclear power station. Everything on Earth is made up of very tiny particles called atoms. Splitting the atoms that make up uranium produces a very intense heat for creating steam.

In a nuclear power station, energy is produced by creating a reaction in the nuclei (cores) of uranium atoms. Releasing energy by splitting atomic nuclei is called fission. Each nucleus contains particles called neutrons. Inside the reactor, these hit other nuclei, causing them to split and release more neutrons. This repeated process, called a chain reaction, produces immense amounts of heat energy. Water pumped around the reactor is heated.

Hydro-electric power stations use fast-flowing water to turn turbines. The water from rivers is stored in a reservoir behind a dam. The power station is located in front of the dam. Some of the water is allowed to rush out through pipes to make turbines spin and drive the generator.

SUPPLYING ELECTRICITY

The electricity is sent from the power station along thick wires called cables. They are supported above ground by tall pylons. The electric current is boosted by transformers along the way. The electricity goes to sub-stations from where cables carry it to houses, factories, shops and offices.

The cables from a power station are linked to form a country’s supply network or grid. This allows electricity to be sent to wherever it is needed. Electricity cannot be stored, so a constant supply flows through the cables and wires.

ALTERNATIVE POWER

Coal and oil-fired power stations cause pollution. Fossil fuels, once used up, cannot be replaced. Leaks of radioactivity from nuclear power stations are a potential hazard. So alternative methods for generating electricity are needed. Wind turbines on wind farms, solar power (in which solar panels store sunlight for conversion to electricity), tidal and wave power are all possibilities for the future.

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Fossil fuels - coal, oil and gas were formed from the remains of living things that died millions of years ago and are preserved as fossils.

Coal began to form about 350 million years ago. At that time parts of the Earth’s surface were covered with swamps and lakes. Forests of huge trees and giant ferns grew in the swamps. When these plants died, they rotted down and gradually changed into a type of dark soil called peat. As the centuries passed the peat was buried under layers of sand and mud. Successive layers pressed down more and more tightly until the peat was compressed into layers of hard, black, shiny rock—coal. Folding and faulting of rock layers, the result of Earth movements over millions of years, together with erosion, have brought some coal layers close to the surface and within reach of underground mines.

Coal was first mined as a fuel on an industrial scale in the 18th century when it was used in furnaces to power steam engines and smelt iron. Today it is used in power stations to produce electricity. Coke, a baked form of coal, is a smokeless fuel used in making iron and steel.

OIL AND GAS

Oil is a very important substance. It is used as a fuel in power stations, cars, ships and aircraft, and is an essential raw material for plastics and chemical industries.

Oil and gas were formed in the seas millions of years ago. When the tiny plants and animals that lived in them died they sank to the bottom and were buried under layers of sand and silt. These were gradually compressed into layers of sedimentary rock. The heat action of bacteria changed the remains into crude oil and natural gases.

Pressures in the Earth force the oil up through the sedimentary rock, which has tiny holes in it like a sponge. The oil rises until it comes to a layer of hard rock. If the hard rock has formed a dome over the soft rock, the oil is trapped under it. Geologists looking for oil study the local rock formations and make test drillings. If oil is found, wells are drilled into the ground. When the drill reaches oil, the pressure may be enough to send it gushing up to the surface. If not, it is pumped. The crude oil from the well is sent by pipeline or tanker to a refinery where it is separated into different substances by distillation.

The oil is boiled at the bottom of a huge tank called a fractionating tower. The vapours that are formed float upwards, cool and condense into liquids at different temperatures. Trays at different heights in the tower collect the liquids as they form. These separate parts, or fractions, are formed into different oil products, such as petrol, kerosene and diesel oil. At the top of the tower, gas comes off. The thickest, heaviest products, such as bitumen, used for making roads, sink to the bottom. They can be refined again to make lubricating oils.

The earth contains many minerals that are vital to us today. Minerals are non-living substances such as rocks and metals found naturally in the Earth's crust.

Some metals, such as gold, can be found at the surface, but others are buried deep in the ground and have to be mined. Copper was one of the first metals to be used by people, but it is brittle and breaks if it is hammered too much. Early metalworkers discovered that if they hammered copper, then heated it in the fire and then hammered it again, it was easier to work with. This was the discovery of a process called annealing.

Some metals have to be extracted from the rock, or ore, in which they are found. The process used is called smelting. The rock is heated to a high temperature so that the metal melts and runs out.

Metals found near the surface are mined by the opencast method but those found deeper down have to be drilled out of the ground. First, geologists determine where the metals are. They carry out surveys of the rock layers beneath the surface, and also measure the magnetism of the rocks and minerals. This is because the magnetic field is stronger in rocks that contain metals such as iron, nickel and cobalt.

INDUSTRY

The word “industry” describes an activity that produces the goods or services that people need or want. There are many different kinds of industry, including mining, farming, fishing, manufacturing and the provision of services for people to use.

Industries fall into three groups. Primary industries are those which extract or grow raw materials, such as mining, fishing, farming and forestry. Manufacturing industries, which turn the raw materials into products such as cars, matches, books and buildings, are known as secondary industries. Tertiary industries include transport, shops, health care, banking, education, leisure and tourism.

In many manufacturing industries around the world, for example, cars, plastics and electrical appliances, machines are used instead of people to make goods. Highly automated industries, as they are called, are using more and more specialized equipment such as electronic technology and industrial robots to increase productivity. This has been partly responsible for increasing unemployment in certain countries. During the last part of the 20th century, Japan and other East Asian countries have developed highly automated industries, including electronics, computers and cars.

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