What non-carbon life forms could be silicon or nitrogen

(ORDO NEWS) — Earthly life, the only one known to us at the present time, is based on a huge variety of carbon compounds. Meanwhile, this is not the only chemical element that can underlie life.

The existence of other forms of life, fundamentally different from our earthly ones in the presence, location and number of paws, eyes, teeth, claws, tentacles and other parts of the body, is one of the favorite topics in science fiction literature.

However, science fiction writers are not limited only to this – they come up with both exotic forms of traditional (carbon) life and its no less exotic foundations – for example, living crystals, disembodied energy field creatures or organosilicon creatures.

In addition to science fiction writers, scientists are also discussing such issues, although they are much more cautious in their assessments.

After all, so far the only basis of life that is precisely known to science is carbon. However, at one time, the famous astronomer and popularizer of science, Carl Sagan, said that it was completely wrong to generalize statements about earthly life in relation to life in the entire universe.

Sagan called such generalizations “carbon chauvinism”, while he himself considered silicon as the most likely alternative basis for life.

The main question of life

What is life? It would seem that the answer to this question is obvious, but oddly enough, there are still discussions about formal criteria in the scientific community.

Nevertheless, a number of characteristic features can be distinguished: life must reproduce itself and evolve, and for this, several important conditions must be met. First, for the existence of life, a large number of chemical compounds are needed, consisting mainly of a limited number of chemical elements.

In the case of organic chemistry, these are carbon, hydrogen, nitrogen, oxygen, sulfur, and the number of such compounds is enormous. Secondly, these compounds must be thermodynamically stable or at least metastable, that is, their lifetime must be long enough for various biochemical reactions to take place.

The third condition is that there must be reactions to extract energy from the environment, as well as its accumulation and release. Fourth, the self-reproducibility of life requires a mechanism of heredity, in which a large aperiodic molecule acts as an information carrier.

Erwin Schrödinger suggested that an aperiodic crystal could be the carrier of hereditary information, and later the structure of the DNA molecule, a linear copolymer, was discovered. Finally, all these substances must be in a liquid state in order to ensure a sufficient rate of metabolic reactions (metabolism) due to diffusion.

That the carrier of hereditary information can be an aperiodic crystal, and later the structure of the DNA molecule was discovered – a linear copolymer. Finally, all these substances must be in a liquid state in order to ensure a sufficient rate of metabolic reactions (metabolism) due to diffusion.

That the carrier of hereditary information can be an aperiodic crystal, and later the structure of the DNA molecule was discovered – a linear copolymer. Finally, all these substances must be in a liquid state in order to ensure a sufficient rate of metabolic reactions (metabolism) due to diffusion.

Traditional Alternatives

In the case of carbon, all these conditions are met, but even with the closest alternative – silicon – the situation is far from being so rosy.

Organosilicon molecules can be long enough to carry hereditary information, but their diversity is too poor compared to carbon organics – due to the larger size of silicon atoms, it is difficult to form double bonds, which greatly limits the possibilities of attaching various functional groups.

In addition, limiting silicon hydrogens – silanes – are completely unstable. Of course, there are also stable compounds such as silicates, but most of them are solids under normal conditions.

With other elements, such as boron or sulfur, the situation is even sadder: organoboron and high-molecular sulfur compounds are extremely unstable, and their diversity is too poor,

What non carbon life forms could be silicon or nitrogen 4

Under pressure

However, recently, while modeling various nitric systems at high pressures (up to 800 GPa) using our USPEX (Universal Structure Predictor: Evolutionary Xtallography) algorithm, our group discovered an amazing thing.

It turned out that at pressures above 36 GPa (360,000 atm), a number of stable nitric hydrogens appear, such as long one-dimensional polymer chains of N 4 H, N 3 H, N 2 H and NH units, exotic N 9 H 4, forming two-dimensional sheets of nitrogen atoms with attached NH 4 + cations, as well as molecular compounds N 8 H, NH 2 , N 3 H 7 , NH 4 , NH 5 .

In fact, we have found that, at pressures of the order of 40–60 GPa, the nitric-hydrogen chemistry in its diversity significantly exceeds the chemistry of hydrocarbon compounds under normal conditions.

This allows us to hope that the chemistry of systems involving nitrogen, hydrogen, oxygen and sulfur is also richer in its diversity than the traditional organic under normal conditions.

Step to life

“Nitrogens can form long polymer chains and even two-dimensional sheets,” explains Artem. “Now we are studying the properties of such systems with the participation of oxygen, then we will add carbon and sulfur to our models, and this, perhaps, will open the way to nitrogen analogues of carbon proteins, even if for starters they are the simplest, without active centers and complex structure.

The question of energy sources for nitrogen-based life is still open, although these may well be some redox reactions that are still unknown to us, occurring under high pressure conditions. In reality, such conditions can exist in the depths of giant planets such as Uranus or Neptune, although the temperatures there are too high.

The conditions for the “habitat” of living beings based on nitrogen compounds may seem extremely exotic to readers.

But it suffices to recall the fact that the prevalence of giant planets in star systems is at least no less than that of rocky earth-like planets. And this means that in the Universe it is our carbon life that can turn out to be much more exotic.

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