The atmosphere is called the cover which protected the planet. The earth's surface is the lower bound of the atmosphere. And here it has no clear upper bound. As a part of an air cover various gases and their impurity are collected.
Composition of the atmosphere
The envelope of air around the Earth arose long ago – about four billion years ago. In fact, it was created from volcanic gases. Modern living organisms could not breathe such air.
For existence of life on our planet very important role is played by such gases as oxygen, water vapor, ozone and carbon dioxide. All of them are present at composition of the atmosphere. If to speak about oxygen, its stocks constantly are replenished at the expense of plants. Accumulation of carbon dioxide results from breath of living organisms, combustion of fuel. Also carbon dioxide is formed in large numbers after volcanic eruptions. As for ozone, it usually appears as a result of electric discharges from oxygen. The share of content of ozone in the atmosphere is very insignificant.
Now the main share of atmospheric air is presented by such gases as nitrogen and oxygen, and their percentage is unequal at all. Content of water vapor in air under certain conditions can lead to formation of clouds and fog. By the way air weight depends on number of water vapor. Unfortunately, at air of big cities there is also a significant amount of harmful foreign impurity (monoxide of carbon, methane). They cause irreparable damage to the modern biosphere.
Structure of the atmosphere
If to speak about structure of the atmosphere, it differs in heterogeneity. In it it is possible to allocate layers which have the features. The lowermost and dense layer is considered a toposfer. In it about 4/5 all atmospheric air are concentrated. In the troposphere there is a formation of clouds and the constant movement of air. Here also human life proceeds. The maximum thickness of the troposphere can reach 17 kilometers. Above the layer under the name a stratosphere is located. In a stratosphere the air which was more rarefied is also practically absent water vapor. Here at the height of 20 kilometers the ozone layer is formed. Over a stratosphere the mesosphere which is characterized by a smaller density of air is located. Further there is a thermosphere. In this layer the so-called polar lights are formed. Also the thermosphere differs with a most high level of temperature up to 1500 wasps. Well and at last, the exosphere is considered the upper atmosphere. The form of its borders differs in absent-mindedness.