Category Social Sciences

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.

Picture Credit : Google

People have been catching fish from the sea, rivers and lakes for thousands of years. Fishing is still a source of food, and an important industry for many people living near the sea. Japan, China and Russia are the largest commercial fishing nations. The world’s major fishing grounds are the areas of relatively shallow waters that lie above the continental shelf – those parts of the Earth’s landmasses that are submerged by ocean waters.

Most sea fish are caught by fishermen working on trawlers. Trawlers are equipped with a large net that is trawled (dragged) along the sea bed. Distant-water trawlers, the most numerous type, can stay at sea for several months. Many of them have freezers so the fish can be gutted and frozen on board. Middle-water trawlers go out for two or three weeks and near-water trawlers for only a few days at a time.

Trawlers catch demersal fish, those kinds that live near the sea bed. North Atlantic trawlers catch cod in the cold waters off Canada, Greenland and Scandinavia. Japanese and American fleets catch tuna in the deep waters of the Pacific Ocean.

Middle-water trawlers catch fish such as halibut and plaice, while near-water vessels catch fish that live in the warmer waters close to shore, such as haddock, plaice, sole and turbot. These boats do not have freezers on board but the fish can be packed in ice to keep them fresh.

Different techniques are used to catch other marine creatures. Lobsters and crabs are caught in small traps called pots. Oysters and scallops are collected with a dredge, a triangular steel frame with a net on it, which is towed along by a fishing boat.

Today, in many traditional fishing grounds numbers of fish are declining fast, the result of overfishing. In the North Atlantic, herring are now almost extinct and there are far fewer cod and haddock. The use of huge factory ships, on which large quantities of fish can be frozen, is severely depleting supplies for local people in developing countries, who rely on fish for their livelihood. There is also concern about the destruction of ocean food chains by overfishing. It is estimated that 20 million tonnes of fish a year are discarded by fishing boats because they are not the right kind – a practice that needlessly reduces stocks of other kinds of fish.

TRADITIONAL FISHING

In some parts of the world, fishermen still go out in small boats and catch fish with hand-held nets, as they have done for centuries. These fishermen catch only enough fish for their local communities.

Whales used to be hunted for their meat and oil. Harpoons and factory ships were used. So many species became endangered that commercial whaling of a number of different species was banned by international agreement in 1986.

Picture Credit : Google

At about the same time as people began to grow crops, they also domesticated wild animals for meat, milk and skins or wool. This was the start of livestock farming.

Cattle are kept for milk and meat. There are about 200 million cattle in India alone, with about 1000 million in the rest of the world. Breeds of cattle can be divided into two main groups: the European breeds, which are descended from a now-extinct species of long-horned wild cattle called the auroch, and the various breeds of zebu, the humped cattle of India.

Animals kept for their wool include sheep, goats, rabbits, and vicunas (a type of llama). Of these, sheep are the most common on farms worldwide. Australia is one of the world’s biggest wool producers. Of the 1000 million sheep in the world, about 140 million are in Australia where, in fact, there are many more sheep than people! Australian farmers keep large herds of sheep on huge sheep stations. Most of the sheep are Merinos, a breed that has soft; thick wool and which can survive on the poor grass that is characteristic of the dry grasslands of central Australia.

Some livestock farmers keep pigs for meat. On large modern pig farms, the animals are kept indoors in controlled conditions and fed a mixture which makes them put on the most weight in the shortest time. About 400 breeds of pig have been produced over the centuries but many of these have now disappeared with the development of intensive farming methods. The main surviving breeds include the Berkshire, Chester White, Poland, China, Saddleback, Yorkshire, Duroc, and Razorback. There are about 800 million pigs in the world, half of them in Asia. Their meat is sold as pork (fresh meat), bacon or ham (cured or preserved meat).

POULTRY

Poultry farmers keep chickens, turkeys, geese and other birds for meat and eggs. Chickens are descended from tropical forest birds found in Southeast Asia. They can be reared by intensive or free-range methods. There are about 7000 million chickens in the world. Good breeds for egg-laying include Leghorns and Minorcas. Dorking and Cornish breeds are good for meat, and Orpingtons and Rhode Island Reds are useful for both. Turkeys, ducks and geese are mainly reared for their meat.