Our planet is surrounded by three shells. The one on which we all live — hard and is called the lithosphere. Rivers, lakes, seas, oceans form a liquid coating — hydrosphere, and envelop her air — a gaseous atmosphere. All three shell sharply demarcated, although penetrate each other. In the XIX century. the idea of the existence of a very special enclosure where born and now live creatures. And because they live both on land and in the water and in the air, the biosphere (living area) has no clearly defined boundaries, occupying the upper layers of the lithosphere and the hydrosphere and the lower layer of the atmosphere. According to the teachings of Academician Vladimir Ivanovich Vernadsky (1863-1945), the biosphere is composed of 1) living matter, that is, living organisms, and 2) the victim of living matter, and 3) of its products by living organisms and decomposition of rocks.
Circulation of substances in the biosphere between soil, atmosphere, plants, microorganisms and animals are called biological cycle. On Earth, it all starts with vegetation — and it ends with. Under the influence of solar trees and other green plants produce organic matter through photosynthesis, which are concentrated in the leaves, stems, roots and fruits. A by-product of organic synthesis — oxygen: this is how the earth flora forms the basis of existence of the earth's fauna. Primary atmosphere of the planet was rich in ammonia and carbon dioxide, oxygen but it was not, and for the fact that today we can breathe, we have to thank only green plants. Animals absorb oxygen during respiration, and the formed with carbon dioxide back to the atmosphere. Synthetic organic plant serves as food for herbivores, rodents and many birds, and those, in turn, eaten by carnivorous predators. Wastes of animals, their dead bodies and remains of plants fall to the soil surface, where the case is taken microorganisms. The result is humus. His decomposed remains of other eaters of dead organisms, and the end product assimilate live plants. Thus, a vicious circle! Biological cycle Earth is continuous and is involved in a large geological cycle of matter between the ocean and the land.
Biological cycle in nature is due to the sun heats the air, soil and vegetation. In this case, the water evaporates, and its vapor, condensing into clouds, finally came back to earth by rain or snow. Rain water is absorbed from the soil by plant roots, and immediately got on the leaves evaporates into the atmosphere. Water has penetrated deep into the soil flows into the layer of ground water and from there enters the water or soil mikrotreschinkam — capillaries — seeps into the soil. Trees of the solar energy is used to convert carbon dioxide into organic matter — the basis of the power of all living beings. In this case, oxygen for breathing animals and humans. In soil, microorganisms transform decomposition products of plants and animals in the simple substance. They are washed with water, partly dissolving in it, and then enter into the ground water.