Environmental Problems

The poisoning of the world’s land, air, and water is the fast –spreading disease of civilization. It probably produces fewer headlines than wars, earthquakes and floods, but it is potentially one of history’s greatest dangers to human life on earth. If present trends continue for the next several decades, our planet will become uninhabitable.

Overpopulation, pollution and energy consumption have created such planet-wide problems as massive deforestation, ozone depletion, acid rains and the global warming that is believed to be caused by the green-house effect.

The seas are in danger. They are filled with poison: industrial and nuclear waste, chemical fertilizes and pesticides. The Mediterranean is nearly dead, the North Sea is following. The Aral Sea is on the brink of extinction. If nothing is done about it, one day nothing will be able to live in the seas.

Every ten minutes one kind of animal, plant or insect dies out for ever. If nothing is done about it, one million species that are alive today will have become extinct in twenty ears from now.

Air pollution is a very serious problem. In Cairo just breathing the air is life-threatening – equivalent to smoking two packs of cigarettes a day. The same holds true for Mexico City and 600 cities of the former Soviet Union.

Industrial enterprises emit tons of harmful substances. These emissions have disastrous consequences for our planet. They are the main reason for the greenhouse effect and acid rains.

Even greater environmental threats are nuclear power stations. We all know how tragic the consequences of the Chernobyl disaster are.

People are beginning to realize that environmental problems are not somebody else’s. They join and support various international organizations and green parties. If governments wake up to what is happening, perhaps we’ll be able to avoid the disaster that threatens the natural world and all of us with it.

Water

Water is one of the most important of all chemical substances. It is a major constituent of living matter and of the environment in which we live. Its physical properties are strikingly different from those of other substances.

Water was thought by the ancients to be an element. H. Cavendish (1731–1810) in 1781 showed that water is formed when hydrogen is burnt in air, and A. Lavoisier (1743–1794) first recognized that water is compound or the two elements – hydrogen and oxygen.

The formula of water is H₂O. The relative weights of hydrogen and oxygen in the substance have been very carefully determined as 2.016:16.000. This determination has been made both by weighting the amounts of hydrogen and oxygen liberated from water by electrolysis and by determining the weights of hydrogen and oxygen which combine to form water.

Water is one of the commonest of all substances, and without it life would be impossible. The seas and oceans cover about seventeenth of the Earth’s surface but water is also contained in the soil, in the atmosphere and in all living things. More than half of the human body consists of water, which also forms a large part of the food we eat, especially vegetables and fruit. Man can live as long as ninety days or more without food, but we cannot live many days without water.

Water exists as a substance in three states: ice, which melts at 0 degrees Centigrade, liquid water and steam, which is formed when water boils at 100 degrees Centigrade.

Water differs from all other liquids in that it expands when cooled from 0° Centigrade, contracts when heated from 0° to 4° Centigrade, and reaches its maximum density at 4° Centigrade. No other liquid possesses this property. Pure water is rarely found in nature. This is because water is able to dissolve so many substances from the air, the soil and the rocks. The saltiness of sea water is caused the by the mineral substances which are dissolved from the Earth’s surface by rivers and carried down to the sea. The Sun’s heat causes the surface sea water to evaporate, or change into vapor, leaving behind the salt and other materials. This explains why the seas are so much more salty than the rivers flowing into them.

Дата добавления: 2015-07-08