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There is such a polemical term as “carbon chauvinism”. This
phrase describes the state of a person talking about extraterrestrial (or terrestrial)
non-protein forms of life, but having at least basic knowledge in the field
of chemistry at the same time. That is, one who understands exactly what consequences,
for example, the replacement of carbon with silicon will lead to. Understanding
it, unfortunately, is categorically incompatible even with minimal optimism
about the possibility of the appearance of silicon-based life.
However, not only silicon can be the basis for the development of carbon chauvinism. You can talk, for example, about hypothetical nitrogen-phosphorus-based life, representing, by the way, the antipode of silicon-based one. For if the advantage of the latter seems to be adaptability to temperatures higher than those suitable for carbon life – a doubtful advantage, since silicon creatures will still need liquid water – then the nitrogen-phosphorus base, on the contrary, makes the living matter insensitive to low temperatures. So, it opens up opportunities for the settlement of worlds where it is too cold for liquid water.
The essence of the concept is that, although necessary for life, but too chemically fierce, phosphorus itself is not suitable as a base for giant macromolecules, and in “coupling” with the nitrogen atom it begins to exhibit properties similar to carbon. But, on the other hand, the properties of a molecule built of nitrogen-phosphorus chains will differ very significantly from the chemistry of RNA. For photosynthesis, “ice” plants will have to use ammonia and phosphine (a compound of phosphorus and hydrogen) instead of carbon dioxide and water. The “waste” of the reaction will be not oxygen, but hydrogen. By consuming it, animals will be able to process organic matter, returning nitrogen and phosphorus to plants.
The most valuable property of the above-mentioned metabolism is the lack of need for water – not only as a reagent for the synthesis of biomass, but also as a solvent in which intracellular reactions take place. Ammonia freezing at -78 degrees, and phosphine – in some conditions not freezing at -200 degrees – can act as a liquid base of nitrogen-phosphorus life. Here it is necessary to emphasize that the use of the word “chauvinist” any number of times, does not cancel at all the fact of necessity of a liquid solvent for life, which is by definition a chemical reaction of autocatalysis, taking place only in a solution.
Technically, the conditions for nitrogen-phosphorus life in the universe are quite common. A suitable environment may be an atmosphere of a giant planet, for example – of Jupiter, at least. Moreover, if we take into account that the circulation of substances in its inherent metabolism is based precisely on hydrogen and is directed “in reverse” (animals inhale fuel, an oxidizer is extracted from food), then these conditions turn out to be favorable. If life on Earth has spent two billion years for transforming the atmosphere from a reducing to an oxidizing one, then for nitrogen-phosphorus creatures the predominantly hydrogen atmosphere is already an analogue of “oxidizing” one. That is, the opportunity for the appearance of large and active animals appears immediately.
However, Jupiter (as well as the subglacial seas on the icy moons, which contain a lot of ammonia) is the base for a high-temperature, “ammonia-soluble” version of the nitrogen-phosphorus fauna. The medium for the low-temperature “phosphine-soluble” version can be oceans of liquid gases, similar to those currently existing on Titan, and in the past even on such cold bodies as Triton and Pluto. Its activity can be detected by the release of hydrogen.
That is, if there were nitrogen-phosphorus life on Titan, the concentration of hydrogen in the lower layers of the atmosphere would be higher than the calculated one. But there, it is actually below the calculated values – as if someone is not releasing this hydrogen, but consuming it. So, carbon chauvinism triumphs here too.
The main disadvantage of nitrogen-phosphorus life remains the same as that of silicon-based one. For its occurrence, the accumulation of building materials is required – the primordial soup, in which the autocatalysis reaction flushes. However, unlike hydrocarbon ones, organosilicon or organophosphorus molecules cannot be produced and accumulated anywhere in the universe in adequate quantities.
Translated by Pavel Volkov, 2021
The original Russian article is here