Trees are an important natural resource, because there is a constant demand for timber for building, for paper and other purposes. In developing countries wood is used as fuel for cooking. Even waste wood can be chipped and mixed with an adhesive under high pressure to form large flat building boards.
Tree felling in some areas has resulted in large-scale deforestation, often followed by erosion. With no tree roots to stabilize it, the soil is washed away by rainfall.
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As we use up natural resources such as coal and oil, there is a constant search for new sources of energy. The Sun gives out vast amounts of energy, of which only a tiny fraction reaches the Earth. If we could use just a small part of this energy it would fulfil all the world’s foreseeable needs for power, but so far it has not been possible to find efficient ways to collect solar energy. We harness the Sun’s energy with solar panels. This energy is then used to heat water.
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Oil is thought to have formed from the remains of organisms that died millions of years ago. Billions of tiny organisms lived in shallow water or in the surface layers of the oceans. As they died their remains settled to the bottom and were eventually buried. The remains were compressed under the weight of rock. They underwent chemical changes due to the high pressure and eventually formed oil and gas, which remained trapped under the rock layers.
Geologists locate deposits of oil, and holes are drilled so the oil can be extracted. Usually, water is pumped into an oil well under pressure, forcing the lighter oil up to the surface.
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Coal is formed from the compressed remains of plants that lived in bogs 250-350 miff on years ago. This was during the Carboniferous Period, when primitive animals first appeared on the land. Coal formed from the remains of tree ferns and other primitive trees, which were covered with mud and sand and buried as new rock was laid down. Very gradually, over millions of years, this material turned into coal.
A similar process is taking place today in peat bogs, where the rotting remains of heather form peat. When dried, peat burns in a similar way to coal. In some parts of the world soft shale, which is called brown coal, is mined. The hardest and most pure form of coal is anthracite, which contains very few impurities.
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Gold is unusual because it is found in its metallic form, rather than as a chemical compound. Metallic gold, which is easy to identify and shape, has been mined for thousands of years. Most gold is found in what are called alluvial deposits. They consist of river mud containing tiny particles of gold washed out of rock over thousands of years. Water currents are used to wash away the mud and gravel, leaving the heavy gold particles. Gold is mined in many parts of the world, but most modern gold supplies come from countries such as South Africa and Russia.
Gold does not tarnish, and this makes it very valuable.lt is used mainly for the manufacture of jewellery and for coating electrical contacts. It is also a very good conductor of electricity.
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The earliest form of mining involved following seams of metal in tunnels driven into the rock. This method is still used today, usually in deep mines where other techniques would be impracticable. Tunnels are dug with explosives and with automatic machines. Some of these mines go thousands of metres into the rock, becoming very hot and dangerous.
Placer mining uses huge floating dredgers to extract metals such as tin and copper from submerged mud. It extracts large amounts of metal inexpensively, but causes enormous environmental damage. Strip mining is used to obtain coal and minerals that lie close to the surface. Open pit mining involves blasting into the rock to produce a huge quarry from which material is removed, layer by layer.
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Mining has taken place since the Stone Age, when flints were mined for making stone tools. By 3500BC, people were mining for copper, which they soon combined with tin to harden it and make tools and weapons. Today we mine minerals, diamonds, metals, coal and rock for building material, using a variety of techniques.
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Cameras work by focusing light in order to produce an image on a light-sensitive surface. Some cameras work by forming the image on light-sensitive film. Sometimes film uses dyes that change colour when exposed to light, as happens with film used to make coloured slides or prints. Earlier film or glass plates used a silver compound as the light-sensitive material. To produce a photographic print the image is projected onto the surface of light-sensitive paper. It is treated with chemicals to make the print visible and prevent further changes when exposed to light.
Digital cameras are a recent development. They convert the image they receive into electrical signals that are stored. These signals can then be read by a computer and used to produce a picture on screen, which can then be printed out.
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Printing is the process by which many copies of words and pictures can be reproduced on paper or other materials. Simple wood blocks with carved letters covered with ink were used to print until around 1440, when Johannes Gutenberg developed movable type (a separate piece of metal type for each character). A machine pressed the inked type against paper.
Most modern printing is carried out by offset printing, or lithography. Images are placed on metal printing plates by a photographic process, and a greasy ink is applied that sticks to the areas where the image will be. The inked image is then transferred to a rubber roller and applied onto paper. Some of the fastest newspaper presses can print at a speed of 900 m of paper per minute.
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Explosives are substances that release a very large amount of energy in a short time when they burn. They all contain a fuel plus an oxidizer, which is a substance containing sufficient oxygen to burn the fuel. Explosives do not need air to explode, because they contain their own oxygen, and so they can burn in confined spaces or even underwater. Some explosives, such as those in a cartridge detonator, explode violently when hit or heated. Others only cause a violent explosion when confined in a gun barrel or a hole drilled in rock for blasting.
Gunpowder, the first ever explosive, was invented in China over 1,000 years ago. Large amounts of modern explosives are commonly used in quarrying and mining, as well as for munitions.
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