Thread between the firm earth and outer space is invisible, its importance for all live on the planet is huge. Minor changes in its chemical composition can lead to origin of new types or extinction of the whole population. A name to it – the atmosphere. Emergence of the atmosphere and its transformation – a combination of unique conditions thanks to which all appeared live on the planet Earth.
Instruction
1. At the very beginning of formation of the solar system (4.5 billion years ago) Earth, as well as other planets, represented the liquid, heated cloud from gas and dust. Gradually the Earth's surface cooled down, crusted, forming a landscape. The seas, the rivers and lakes did not exist, in Earth continuously there were thermonuclear processes. The firm Earth's surface was still too thin therefore the heated cloak and gases without effort broke on a surface. Over time these gases also formed the atmosphere since because of Earth attraction they could not "depart" to space.
2. At that time the atmosphere consisted generally of ammonia, methane and carbon dioxide. The ozone layer was not, in addition, evaporations of water hung over a surface the continuous huge cloud enveloping all planet. Such conditions still were not suitable for life. And only when clouds spilled rains and filled terrestrial hollows, the seas and oceans were formed. In them later millions of years the life began to arise.
3. There are many theories of emergence of life, as the most convincing are considered "meteoric" and the theory of "self-generation". Anyway all meet in one – life arose in the ocean since only ocean depths could protect the first sprouts of life from pernicious ultraviolet rays.
4. The first organisms reminded modern bacteria, ate the organic matter dissolved in water and quickly bred. There passed some more million years and "bacterium" learned by means of a chlorophyll, using sunlight, to create substances, necessary for life.
5. Absorbing carbon dioxide, they emitted oxygen. This process is called photosynthesis. As a result of photosynthesis, oxygen was emitted in the atmosphere, and in its top layers turned into ozone. Gradually ozone layer was thickened, closing access to ultraviolet rays. Thanks to it living organisms could come out of the water subsequently.
6. The modern atmosphere has thickness about 3000 km, contains 78% of nitrogen, oxygen - 21% and a small amount of helium, carbonic and other gases. Was considered that volcanoes have the greatest influence on a condition of the atmosphere. However It should be noted that in the last decades the person laid a hand to change of the atmosphere.
7. In the large cities because of the working plants and exhaust gases the people, in literal sense, have nothing to breathe. Researchers were divided into two camps: some consider that greenhouse effect – result of human activity. Others are sure that greenhouse effect - the phenomenon natural, and in comparison with eruption of one volcano, human activity is incomparable.