Soil is the ‘place’ where materials essential for ecological equilibrium are formed and decompose, but it is also where our food is produced. Unfortunately, it is also the waiting room of a number of environmental problems that begin in it and terminate elsewhere.  Nevertheless, studies regarding soil biology (pedobiology), respect to those regarding let’s say, air and water, are still rather slow: why?
The main reason is that the scientist perceives Nature in the same manner as everyone else, which is not always the correct way of understanding it. In other words, to understand Nature well, one must go beyond what one can see (or hear), and understand Nature by using simple reasoning. Let us consider for example our difficulty in imagining the many processes that take place at a microscopic or sub-microscopic level, such as those that occur in the sphere of cells; or the difficulty in adapting our way of perceiving the passing of time to the scale of biological evolution, that is measured in hundreds of millions of years. Well, these limits have represented one of the most important factors in the orientation of scientific research, in some cases with results that were rather negative for our knowledge: which is the case of soil biology.     
An environment full of life
Even though not much is known about soil organisms, it is certain that soil is not an inert and sterile environment but, on the contrary, it is a dynamic one overflowing with life. The majority of the organisms live within the first metre in depth and, in general, the biological spaces they occupy and their biological activities are on a very small scale. The growth of cultivated plants, for example, depends on the way in which the solid particles of the soil are arranged  to allow the formation of spaces with a diameter of about 0.2 mm. Moreover, these plants depend on the activity of micro-organisms that are about 1 µm (1,000 µm = 1 mm) in size, to contribute nutrient substances such as nitrates.
Soil is a resource of great environmental value, and at the same time, it is also an ecological system that recovers with difficulty each time its health is harmed by pollution produced by Man. It carries out an extraordinary activity of preservation of ecological equilibriums and plays a crucial role in the protection of human health. A proof is its complex activity as a biological and chemical filter, capable of slowing down and limiting dangerous chemical pollutants that, penetrating from the more superficial layers towards the deeper ones, could reach the layer with the water that we drink.
As far as the inorganic chemical composition and the structure of soil are concerned the reader can refer to these topics discussed in the section ‘Earth’.

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