Soil’s importance as environment for Earth’s animals consists in the fact that many live species’ existence is connected to it. Numerous organisms that inhabit soil are presented by microorganisms (bacteria, fungi, actinomyces, algae, protozoan), vertebrate and invertebrate animals. Bacteria are most widely represented among soil’s microorganisms. Live weight in ploughing horizon is from 3 to 6-7 tones per hectare. The quantity of bacteria in soil depends from its type and cultural state. The number of bacteria decreases with depth. They are especially numerous in upper horizons that are rich in organic matter. Organic matter regime and accumulation in biosphere is remarkable feature of soil environment, providing soil’s capacity as storage and source of matter and energy for terrestrial organisms. Earth’s soil cover, according to M.M. Cononova (Круговорот вещества в природе .., 1980), contains nearly 2500 milliard tones of humus. Annual synthesis of humus matter in terms of carbon content is equal to 1-2 milliard tones. Humus supply forming period is nearly 800-1500 years. In present due to wide reclamation of soil cover and soils erosion’ intensification, humus’ world deposit is in decrease. The annual rate of decrease is 1.2-1.4 milliard tones, and over last 100 years nearly 400 milliard tones of humus is lost. The decrease of rate of humus’ de novo synthesis is also registered due to decrease in leaf-fall supply by more than 40% because of agricultural activities. Soil also plays a key role in evolutional process, as soil cover according to its main ecological particularities can be viewed as transitional environment (between air and water one), through which gradual transition from aquatic habit of life to terrestrial one without rapid changes in organization of breathful. Some larger animals (earthworms, grubs of some bugs, centipedes et al) inhabit soil as their environment as a whole, serving as porous or compact medium. In the case of a compact medium there is a necessity in special morphological adaptation for digging and tunneling. It also should be mentioned that larger animals depend on the whole more from soils’ cluster of features than the inhabitants of microscopic soil reservoirs (protozoons et al) and the inhabitants of leads and cavities (ticks et al). The fact that soil is a diverse environment for various dimensional groups of animals is of great importance when understanding soil’s specifics as a special natural formation. Such heterogeneity of soil testifies that practically all main types of ecological niches are close inside it in a confined space. The diversity of soil’s environment is a factor that contributes to such common regularity as changes in horizons: many animals that usually live on the surface proceed to life inside the soil when landscapes humidification decreases. Thus soil-inhabiting grubs of Tenebrionidae and Alleculidae appear widely in chernozems, but in the conditions of deciduous forests another species of these family are developing in decaying wood. Soil grubs of Dorcadion, Eumalpmae and many other forms that belong systematic groups the representatives of which do not inhabit soils of forest biogeocenosis also appear in soil. Furthermore, the ants that live in dryer places, build deep underground nidus in steppe. For larger non-microscopic, but still lesser organisms, soil as habitat is presented by an assemblage of leads and cavities, the movement in which is similar to movement on substrate’s surface. Soil’s porosity, its water and thermic regime, distribution of debris and humus is of most importance for this category of soil’s inhabitants. Above-ground mode of life requires serious adaptation changes that are hardly achievable at sharp transfer from water environment to above-ground mode of life without intermediate link – soil. For certain group of animals such transfer would be impossible, which would lead to decrease in biological evolution rate and its simplification, e.g. the present diversity of above-ground forms that exist at present would not be possible without soil. As one considers anthropogenic changes of functions of soil as environment (loss of soils due to erosion, desertification etc), one can state terrestrial organisms’ pedological living conditions’ worsening and total decrease in livable space. One can also state the decrease in soil-ecological niches’ diversity as a result of progress in degradation processes. Simultaneously new anthropogenically conditioned soil-ecological niches appear, part of which is favorable for terrestrial organisms (soils under artificial afforestations, successfully meliorated lands et al). Together with decrease in terrestrial species’ number, down to complete vanishing, new populational structures appear, new man-created place of habitat are reclaimed, which contributes to modern biological evolution features unusual for its natural development. Soil degradation leads to fauna degradation.