BIOSFERA. — From the Greek βίος (= life) and σφαῖρα (= sphere). The term b. was used to designate the further indivisible spherical corpuscle, belonging to a hypothetical existence that would have constituted the basis of all organized beings.
In 1835 E. Suess introduced into geography the concept of the b. to designate a kind of envelope, impregnated with life, that surrounds the entire earth’s crust.
By b. we mean that part of the atmosphere, lithosphere, and hydrosphere in which the marvelous phenomena of life take place, occurring in an equally perfect manner both in those infinitely small beings visible only under the ultramicroscope, some of which are formed by a single protein molecule in the colloidal state, such as viruses, and in the giants of nature, such as the eucalyptus trees 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; using inorganic materials taken from the environment (water, salts, carbon dioxide), they manufacture organic substances that subsequently become organized. In the process of photosynthesis, which lies at the basis of all plant syntheses, green plants purify the air by removing from it the carbon dioxide produced by animal and plant respiration and by combustion, and returning oxygen in exchange. Solar energy is used in this process. Thus the plants, with the various substances manufactured and stored in their bodies, become the basis of nourishment for the animal world, which lacks these powers of synthesis.
Some plants send their roots several meters into the ground, fragmenting rocks and sometimes displacing blocks of considerable size. The roots also modify the chemical composition of the soil by preferentially taking up some of its chemical constituents over others, and even by solubilizing certain insoluble materials, either by causing the release of small quantities of strong acids at the expense of the salts dissolved in the water, whose cation they absorb more rapidly (the ion-selection power), or through the action of carbon dioxide produced by their respiration. The superficial layers of the soil teem with an entire population of microorganisms, among which are bacteria that fix elemental nitrogen (Bacillus pasteurianus, Azotobacter chroococcum, and A. agile), and those that transform organic matter deriving from the waste of animal and plant life into inorganic materials, such as carbon dioxide, water, hydrogen sulfide, phosphates, and ammonia. The latter is then, through the action of other bacteria (Pseudomonas europaea, P. Gavanensis, Micrococcus nitroococcum), oxidized into nitrous acid, which, on contact with the bases in the soil, is transformed into nitrites; these are then oxidized into nitrates by other bacteria (Bacterium nitrobacter), and can be used effectively by higher plants. Other bacteria, finally, carry out the reverse process: they reduce nitrates to nitrites, such as ammonium nitrite, and subsequently decompose this into water and elemental nitrogen.
Basins, watercourses, seas, and oceans are likewise populated by plants, both higher plants and green, brown, or red algae. The latter can descend to approximately 300 m. in depth, that is, as far as a quantity of solar energy that can still be utilized can reach.
Animals live on the earth’s crust; they hide in the soil, in fissures in the rocks, among boulders, in natural caves, among the branches and leaves of plants, etc.; some construct their own dwellings, to which they carry food and fragments for their nests or resting places. Some animals also soar through the air, and the height of their flight depends on the condition of the atmosphere and on the winds. It is known that the condor and the griffon reach heights of up to 6,000 m., the kite 4,000, eagles 4,500, pigeons 2,500, storks 1,500, and swallows 800.
Other animals, the amphibians, live on land and in water; others, such as cetaceans, live in water but, being equipped with lungs, must periodically come to the surface to breathe atmospheric air. Other animals, finally, inhabit only fresh or salt waters; some marine fish populate the depths: Grimaldichthys profundissimus was caught at a depth of 6,035 m. south of Cape Verde.
Some animals can contribute to the formation of the earth’s crust. For example, in the fauna of the torrid zone and, in general, no farther than 28° latitude, we find corals, which, with the calcareous substance secreted by the base of the body of the individual polyps and taken up from the calcium bicarbonate dissolved in seawater, generate the calcareous skeletons of the colonies. As these develop ever further, they ultimately bring about the formation of true barriers, separated from the coast by a channel, or of rings around islets, or, finally, of ring-shaped islands called atolls, formed by a coral bank surrounding a central lagoon. In these banks, the living part of the colony is the most superficial and may reach a depth of approximately 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 pelagic forms; others, finally, extremely small, for the most part microscopic and lacking their own means of locomotion, live in great abundance at the surface of the water and form the plankton. This is the principal 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, through the accumulation of their siliceous skeletons, the formation respectively of diatomaceous earth and tripoli. These deposits, existing today at the earth’s surface, reveal the existence in distant ages of the beds of basins that have since emerged.
The muddy floor of the ocean, at a depth of 1,000 to 5,000 m., consists instead predominantly of numerous calcareous skeletons of Globigerina, protozoa belonging to the group of foraminifers, which enter into the composition of the pelagic fauna.
In the waters, precisely in relation to the increasing abundance of flora in the ever more superficial layers, owing to the penetration of a greater quantity of solar rays, the fauna becomes richer and more abundant as we approach the surface, whereas the animals inhabiting the greatest depths must feed predominantly on the other dead organisms that continually fall from the surface.
In the various biological environments, we can always observe the perfect harmony between the form and internal organization of the various beings, in relation to the conditions of life and external factors. Thus both plants and animals belonging to very different systematic groups may assume a similar appearance in relation to identical environmental conditions, through phenomena known as convergence. This is why the stem of the Cereus of Mexico and that of Enphorbia abyssinica of East Africa lose their leaves, become fleshy and 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 reduced enormously, almost causing the neck to disappear, since its presence is unfavorable to the effort the animal makes to cleave the water. In cetaceans, too, the body becomes tapered at both ends, as in fish, precisely through phenomena of convergence.
Finally, other organisms, sometimes belonging to extremely distant groups, and even plants and animals, associate with one another; symbioses are thus established, to the mutual advantage of both parties (mutualistic symbiosis), or to the advantage of one party and the detriment of the other (antagonistic symbiosis or parasitism). Such, for example, is the nature of the association of pathogenic Viruses, bacteria, fungi, or protozoa, etc., with animals and plants. These parasitic beings are the direct cause of the diseases and death of many other organisms.