BIOSPHERE. - From the Greek βίος (= life) and σφαῖρα (= sphere). It was intended to call b. the spherical corpuscle further indivisible, belonging to a hypothetical existence, which would have been at the basis of all organized beings.
In 1835 E. Suess introduced into geography the concept of b. to indicate a sort of envelope, impregnated with life, that wraps around the entire Earth's crust.
By b. we mean that part of the atmosphere, of the lithosphere and of the hydrosphere in which the marvelous phenomena of life take place, which occur in an equally perfect manner in those infinitely small beings visible only under the ultramicroscope, some formed by a single protein molecule in the colloidal state, such as the viruses, as well as in the giants of nature, like the eucalyptus of Australia and the sequoias of America, which exceed one hundred meters in height (up to 150 m).
As is well known, animal life is closely linked to that of green plants; they, with the inorganic materials taken from the environment (water, salts, carbon dioxide), manufacture organic substances that subsequently become organized. In the process of photosynthesis, which is at the basis of all plant syntheses, green plants purify the air, removing from it the carbon dioxide that comes from animal and plant respiration and from combustions and returning to it, in exchange, oxygen. In this process, solar energy is used as energy. And now behold the plants, with the various substances manufactured and stored in their bodies, becoming the basis of the nutrition of the animal world, which does not have such capacities for synthesis.
Some plants with their roots penetrate a few meters deep into the soil, shattering rocks and sometimes displacing masses of considerable dimensions. Roots also modify the chemical constitution of the soil by taking up some of its chemical constituents in preference to others and even solubilizing some insoluble materials, whether by bringing about the release of small quantities of strong acids at the expense of the salts dissolved in water, of which they absorb the cation more rapidly (power of ion selection), or by means of the action of carbon dioxide, produced by their respiration. In the surface layers of the soil swarms a whole population of microorganisms, among which are the bacteria that fix elemental nitrogen (Bacillus pasteurianus, Azotobacter chroococcum and A. agile), those that transform the organic substance coming from the wastes of animal and plant life into inorganic materials, such as carbon dioxide, water, hydrogen sulfide, phosphates, ammonia. This, then, through the action of other bacteria (Pseudomonas europaea, P. Gavanensis, Micrococcus nitroococcum) is oxidized into nitrous acid, which, on contact with the bases of the soil, is transformed into nitrites, which are then oxidized by other bacteria (Bacterium nitrobacter) into nitrates, which can be well utilized by higher plants. Other bacteria, finally, carry out the reverse process, that is, they reduce nitrates to nitrites, such as ammonium nitrite, and subsequently decompose this into water and elemental nitrogen.
Basins, watercourses, seas, and oceans are also populated by plants, both higher ones and by green, brown or red algae. The latter can reach down to about 300 m. in depth, that is, as far as a quantity of solar energy still usable can reach.
Animals live on the Earth's crust; they hide in the soil, in the crevices of rocks, among boulders, in natural caves, among the branches and leaves of plants, etc., and some build their own dwellings, where they transport food and fragments for their nests or lairs. Some animals also soar in the air, and the height of their flight depends on the state of the atmosphere and on the winds. It is known that the condor and the griffon vulture reach up to 6,000 m. in height, the kite to 4,000, eagles to 4,500, pigeons to 2,500, storks to 1,500, swallows to 800.
Other animals, the amphibians, live on land and in water; others, like the cetaceans, live in water, but being provided with lungs, they must from time to time come to the surface to breathe atmospheric air. Other animals, finally, inhabit only fresh or salt waters; some marine fish populate the abysses: Grimaldichthys profundissimus was caught at 6,035 m. in depth south of Cape Verde.
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Some animals can contribute to the formation of the Earth's crust. For example, in the fauna of the torrid zone and, in general, not beyond 28° of latitude, we find corals, which with the calcareous substance secreted from the base of the body of the individual polyps and taken from the calcium bicarbonate dissolved in seawater, generate the calcareous skeletons of the colonies. These, developing more and more, end up bringing about the formation of true barriers, separated from the coast by a channel, or of rings around islets, or, finally, of annular islands, called atolls, formed by a coralligenous bank that surrounds a central lagoon. In these banks the living part of the colony is the most superficial one and can reach down to a depth of about 20 meters.
Some animals and plants live on the bottom of the sea or of freshwater basins and form the benthos; others swim far from the bottom, near the surface between two layers of water, one upper and one lower, and constitute the pelagic forms; others, finally, very small, largely microscopic and devoid of their own means of locomotion, live in great abundance at the surface of the water and form the plankton. This is the main source of food for aquatic animals, such as pelagic fish and whales.
Some microscopic plant forms, such as diatoms, or animal forms, such as radiolarians, have brought about, with the accumulation of their siliceous skeletons, the formation respectively of fossil flour and of tripoli. These deposits existing today on the Earth's surface reveal the existence in distant epochs of bottoms of basins that are today emerged.
The muddy bottom of the ocean, at a depth of 1,000 to 5,000 m., is formed instead preferentially by numerous calcareous skeletons of Globigerinae, protozoans belonging to the group of foraminifera, which enter into the constitution of the pelagic fauna.
In waters, precisely in relation to the becoming more abundant of the flora in the increasingly superficial layers, due to the penetration of a greater quantity of solar rays, the fauna becomes richer and more abundant as we approach the surface, while the animals that inhabit the greatest depths must feed predominantly on the other dead beings that continually fall from the surface.
In the different biological environments we can always observe the perfect harmony between the form and the internal organization of the various beings in relation to the conditions of life and to external factors. Thus both plants and animals belonging to very different systematic groups can assume a similar appearance in relation to identical environmental conditions, through phenomena called convergence. It is for this reason that the stem of the Cereus of Mexico and that of Euphorbia abyssinica of East Africa lose their leaves, become fleshy, green and assume the same columnar appearance, because they live in equally arid environments.
The cervical vertebrae of cetaceans, while remaining seven in number, as in all mammals, are enormously reduced, almost to the point of making the neck disappear, the presence of which is unfavorable to the effort the animal makes to cleave the water. Always in cetaceans the body becomes tapered at both ends, as in fish, precisely through phenomena of convergence.
Other organisms, finally, sometimes from very distant groups, and even plants and animals, associate with one another; symbioses are thus established, with mutual advantage (mutualistic symbiosis), or with advantage to one party and harm to the other (antagonistic symbiosis or parasitism). Of this nature is, for example, the association of pathogenic viruses or bacteria, or fungi, or protozoa, etc., with animals and with plants. These parasitic beings are the direct cause of the diseases and death of many other organisms.
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Giuseppina Dragone Testi