Man is a carbon-based creature. What would it be like if he evolved from other elements?

Some people say that there are non-carbon-based organisms on the seabed, which have been discovered.

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One of the conjectures is sulfur!

In that world ~ they breathe oxygen and exhale sulfur dioxide (they probably don't need vision or have extraordinary vision).

Of course, we eat foods with extremely high sulfur content, and the photosynthesis of plants also needs to purify sulfur dioxide.

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Carbon-based organisms are unstable and easily decomposed into carbon atoms by high-frequency electromagnetic waves.

Please do something.

How should evolution avoid disintegration from molecules in space?

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Some science fiction writers imagine that living things can also be made of non-carbon-based compounds. The most common thing is to imagine silicon-based life based on silicon compounds, which makes sense. Because silicon and carbon are the same group of elements with similar chemical properties, they can also form polymer compounds under certain conditions. However, at least under the usual energy standard, the activity of silicon compounds is far less than that of organic compounds. However, the high energy standard has some problems such as stability.

In any case, under the existing knowledge, the possibility of non-carbon-based life is very low, even if it is certain, it is very different from the existing life.

Others believe that if computers can achieve advanced artificial intelligence, they can also be regarded as silicon-based life.

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1, in fact, silicon-based compounds are more stable than carbon-based compounds (under dry conditions);

2. I think this problem can also be discussed from the metabolism of organisms: systems (including organisms) have the ability to exchange energy with the outside world, and organisms are constantly oxidized from birth to death (athletes die early); One of the metabolites of carbon-based organisms is CO2, which is easily excreted. The metabolite of silicon-based organisms is SiO2, which seems to be not an easy thing to excrete;

3. Water is an important element for regulating the biological environment and a necessary condition for most chemical reactions; Carbon-based compounds are relatively stable in water (most organic substances are insoluble in water), and the stability of silicon-based compounds in water will be greatly reduced;

4. Most of the basic compounds of carbon are optically active substances (which can produce polarized light), so molecules are easy to produce left-handed and right-handed, and molds rely on this characteristic to identify the metabolic process of organisms; Silicon-based compounds belong to a few optically active substances.

I believe in the existence of silicon-based organisms, because life forms are diverse, and silicon-based organisms have the possibility of its existence; However, it is unlikely that human beings will naturally become silicon-based. Silicon-based organisms should be thermophiles. Now the earth's environment is not suitable for their survival, but the possibility of making silicon-based organisms in the laboratory is not ruled out.

Nonsense, don't laugh at me.

Exploring alien life-non-carbon-based life

All life on earth is based on carbon and water, and it is likely that most life forms in the universe are also based on carbon and water. However, many people believe that other elements besides carbon and other media besides water can also provide the basis of life. As early as 1885, Irish astronomer and mathematician Robert? Stewell? Paul (Robert Stawell Bauer) once mentioned in his Story of Paradise that extraterrestrial life may be completely different from life on earth. He wrote:

"If we can get the opportunity to observe some celestial bodies at close range, we may find that they are also full of life, but they are specialized life that adapts to the environment. Strange and weird life forms ... "

First, silicon-based life

When it comes to life forms other than carbon-based life, people who know a little about it first think of silicon-based life. But when did the concept of silicon-based life come into being? Probably, few people know about it. It would be a surprise to say it. It turns out that this concept appeared as early as19th century. 189 1 year, the astrophysicist Julius of Potsdam University? Julius Scheiner discussed the possibility of life based on silicon in one of his articles. He may be the first person to mention silicon-based life. This concept was developed by British chemist James? Emerson? 1893 was accepted by James Emerson Reynolds, who pointed out in a speech of the British Association for the Advancement of Science that the thermal stability of silicon compounds enables life based on it to survive at high temperatures.

Herbert, a famous British science fiction writer? George? Herbert george wells absorbed Reynolds and Bauer's point of view, he wrote:

"People will be shocked by the strange imagination brought by this idea: since there is silicon-aluminum life, why not think of silicon-aluminum people immediately? Let's just say that they walk in the atmosphere of sulfur-containing gas and wander in the ocean of molten steel whose temperature is several thousand degrees higher than that of the furnace. "

Thirty years later, the British geneticist John? Burton? Sanderson? John Burdon Sanderson Haldane suggested that life based on semi-molten silicate may be found deep in the planet, and the oxidation of iron provides them with energy.

At first glance, silicon is indeed a promising element, which can be used as a substitute for carbon to form life. It is widely distributed in the universe, and its position is just below carbon in the periodic table of elements, so it is similar to many basic properties of carbon. For example, just as carbon can combine with four hydrogen atoms to form methane (CH4), silicon can also form silane (SiH4), silicate is an analog of carbonate, trichlorosilane (HSiCl3) is an analog of chloroform (CHCl3), and so on. In addition, these two elements can form long chains or polymers, in which they are arranged alternately with oxygen. In the simplest case, the carbon-oxygen chain forms polyacetal, which is usually used to synthesize fibers, while the skeleton formed by silicon and oxygen produces polysiloxane.

Based on the above situation, some specific life forms may be composed of silicon-like substances. Silicon-based animals probably look like active crystals, just like Dickinson and skyler drew the following imaginary picture. This is a silicon-based animal wandering among silicon-based plants. The structural parts of this creature may be strung together with silk threads similar to glass fibers and connected by muscle blocks in the middle, forming a flexible, exquisite and even thin and transparent structure.

It seems that these crystalline creatures are very beautiful. If they can survive at room temperature, probably many people on earth are willing to keep a few for decoration at home. One obvious advantage of keeping this pet is that it will not spread bacteria and parasites, because bacteria and parasites, as carbon-based life, are powerless to this completely different life. However, the possibility of life on silicon is threatened by many defects.

A big disadvantage is the strong binding force between silicon and oxygen. When carbon is oxidized during the respiration of living things on earth, it will form carbon dioxide gas, which is a kind of waste that can be easily removed from living things. But the oxidation of silicon will form a solid, because when silicon dioxide is first formed, it will form a lattice, so that each silicon atom is surrounded by four oxygen atoms, instead of each molecule being independent and free like carbon dioxide. Dealing with such solid substances will bring great challenges to the breathing process of silicon-based life.

As long as it is a life form, it is necessary to collect, store and use energy from the external environment. In carbon-based organisms, the most basic compound for storing energy is carbohydrate. In carbohydrates, carbon atoms are linked into chains by single bonds. A series of oxidation steps of carbohydrates controlled by enzymes will release energy, and waste will produce water and carbon dioxide. These enzymes are large and complex molecules, which catalyze specific reactions according to their shape and left and right rotation. Here, the left-handed and right-handed molecules are caused by the asymmetry of carbon contained in the molecules, which is shown by most substances in carbon-based organisms, which enables enzymes to recognize and regulate a large number of different metabolic processes in carbon-based organisms. However, unlike carbon, silicon can not produce many levorotatory and dextrorotatory compounds, and it is difficult to become a supporting element for a large number of interconnected chain reactions needed by life.

In addition, silicon chains are unstable in water and easy to break, unlike carbon chains, which remain stable in dry and humid environments. Although this will not rule out the possibility of silicon-based life, a planet with a lot of liquid water will definitely rule out silicon-based life.

The existence of silicon-based life, even the possibility of early biochemical evolution before the emergence of silicon-based life, is very low, which is also verified by astronomical observations. No matter where astronomers search-meteorites, comets, the atmosphere of giant planets, interstellar matter, the outer layer of cooling stars-they can only find silicon oxide (silicon dioxide and silicate), but can't find substances like silane and silicone as precursors of silicon biochemical existence. On the contrary, it is not difficult to find carbon-based organic molecules such as amino acids in meteorites when we look for signs of carbon-based life. As for methane, it exists not only in many planets and satellites in the solar system, but also in interstellar matter and nebulae. Even in interstellar matter, complex molecules such as methylacetylene and cyanopentyne can be found.

Even so, it is necessary to point out that silicon may have played a certain role in the origin of life on earth. There is a strange phenomenon that life on earth especially likes to use dextrose and L-amino acids. One theoretical explanation for this is that the first batch of carbon compounds in the early evolution of life were formed in a "primitive soup" on the surface of silicon dioxide with a specific rotation (optical rotation), and the rotation of this silicon compound determines the rotation of carbon compounds we now find in life on earth.

Although from the biochemical point of view, the possibility of finding silicon-based life is very small. But silicon-based life is very prosperous in science fiction, and many descriptions by science fiction writers will put forward many useful ideas about silicon-based life. In Stanley? In Stanley Weisbaum's A Roaming on Mars, the age of life is 1 long live, and a stone will be deposited every ten minutes, which is exactly Weisbaum's answer to a major problem facing silicon-based life. A scientist observed in this paper observed:

"Those bricks and stones are its waste ... we are made of carbon, our waste is carbon dioxide, this thing is made of silicon, and its waste is silicon dioxide-silicon dioxide. But silica is solid, so it is masonry. In this way, it covers itself, and when it is covered, it moves to a new place to start again. "

In the Star Trek series "Devil in the Dark", miners in Janus IV discovered a silicon-based life form-Horta. Every 50,000 years, all Hota will die, leaving only one living individual to look after the eggs of the next generation.

It seems that an important idea of life on silicon is longevity, which probably comes from the impression that human beings get from the permanence of natural rocks. Another common view is that silicon-based life is likely to appear on planets with higher temperatures, such as planets full of volcanoes, because many silicon-based compounds are more stable than carbon-based, for example, silicon-oxygen bonds can withstand temperatures of about 600K, while silicon-aluminum bonds can withstand temperatures of nearly 900K, so they have better high-temperature resistance, are relatively stable at high temperatures, and have better activity. For silicon-based life, it takes 200 degrees or even 400 degrees to make them feel comfortable, and they are likely to freeze to death at room temperature where we feel comfortable. That's why when I mentioned raising silicon-based pets, I specifically mentioned the phrase "if they can survive at room temperature".

Second, amino life.

This is a very interesting cartoon. A UFO crashed in the desert of a planet. An alien fell to the ground after trekking in the desert. His mouth was wide open because of thirst. The following caption is his cry in thirst:

"Ammonia! Ammonia! "

Ammonia! Ammonia!

It seems that aliens need to drink ammonia to survive, just as we humans need to drink water to survive.

1954, Haldane, the same British scientist mentioned earlier in this paper, discussed the origin of life at a forum and proposed that water, the solvent used in our life forms, can be replaced by liquid ammonia in some life forms. One of his reasons is that some characteristics of water are similar to ammonia. For example, methanol (CH3OH) may be formed based on water, and methylamine (CH3NH2) may be formed based on ammonia. Methanol and methylamine are just analogues. Haldane proposed theoretically that the corresponding systems of a series of complex compounds based on ammonia can be established, such as the corresponding substances of protein and nucleic acid. With this system, a whole set of organic compounds and peptides can also exist in the amino system. As substitutes for common amino acids, these amino molecules can be polymerized to form polypeptides, and these ammonia-based polypeptides can be consistent with their counterparts found in life forms on earth.

This assumption was made by the British astronomer v? Axel. With the further development of V. Axel Firsoff, he especially considered the world rich in ammonia, such as giant gas planets and their satellites in the solar system (we have found them outside the solar system for more than ten years now), and thought that the development and evolution of such life would be a very interesting topic.

Compared with water, liquid ammonia does have many remarkable chemical similarities. Using the dissolution of ammonia instead of water can provide the whole organic and inorganic chemical reaction, and liquid ammonia is as good as or even stronger than water in dissolution. Compared with water, it has excellent solubility for various metal elements, including alkali metals such as sodium, magnesium and aluminum, and can be directly dissolved; In addition, some other elements, such as iodine, sulfur, selenium and phosphorus, have certain solubility in liquid ammonia and hardly react with liquid ammonia. All the above elements play an important role in biochemistry and pave the way for the early evolution of life.

The boiling point of liquid ammonia is MINUS 34 degrees Celsius at one atmosphere, so such life may need to survive in a relatively low temperature world. There are many such worlds, so this is not its shortcoming. But some people think that the real disadvantage is that the temperature range of liquid ammonia is too small. Because the freezing point is -75 degrees Celsius at one atmospheric pressure, the temperature range of liquid is only 4 1 degree Celsius, which is less than half of water 100 degree Celsius. However, like water, the atmospheric pressure on the planet's surface will increase the liquid temperature zone. For example, at 60 atmospheres (far below the surface pressures of Jupiter and Venus), the boiling point of liquid ammonia will become 98 degrees Celsius instead of -34 degrees Celsius, and the liquid temperature zone will also be expanded to 175 degrees Celsius. Amino life may be life under high pressure.

Molecular structure of ammonia

The dielectric constant of ammonia is about 1/4 of that of water, which makes its insulation performance poor. On the other hand, ammonia has a high heat of fusion and is not easy to freeze (solidify) at the melting point/freezing point. The specific heat capacity of ammonia is quite high, higher than that of water, and its viscosity is low. The study of acid-base chemical reaction of liquid ammonia shows that its details are as rich as water system. In many ways, liquid ammonia, as the carrier of life, is absolutely not worse than water.

However, despite many similarities, the development route of carbohydrate life in liquid ammonia system will still be very different from our water system. Liquid ammonia and water, as solvents bearing the development of life, both need to dissolve the substances needed for life to form cations and anions in order to carry out acid-base reaction, but the acidity and alkalinity of the same substance in liquid ammonia system and water system are probably completely different. For example, the interaction between water and liquid ammonia will produce NH+ ions, which show strong acidity. In this way, the neutral water on which our life depends will become a deadly poison when it comes to amino life. For aliens with amino life, our earth must be a terrible planet, with a huge ocean of hot acid and often boiling acid rain. They probably won't be interested in the earth, and they won't launch an interstellar war with the people of the earth in order to compete for the earth's resources. It is better for them to stay away from such a hellish planet.

So we have to understand that water and liquid ammonia are not the same, they are just similar. Many biochemical characteristics in the two systems are necessarily different. For example, Moreton suggested that amino life forms may use cesium and rubidium chlorides to regulate the potential of cell membranes. These salts are more soluble in liquid ammonia than potassium salts and sodium salts used in life on earth. It seems that the chlorides of cesium and rubidium may be delicious seasonings for aliens living in amino groups, just as we humans use sodium chloride as salt to flavor. But cesium and rubidium are far less abundant than potassium and sodium. Will people there wage war for delicious spices? This should be an interesting topic.

However, the emergence of amino life also encountered some difficulties. Although the heat of fusion of ammonia is higher than that of water, its vaporization heat is only half that of water, and its surface tension is only 1/3 of that of water. These are all attributes related to life. The heat of evaporation and specific heat jointly determine the ability of solvents to regulate the temperature of organisms. High water is good for life. Surface tension is the expression of the imbalance of molecular polymerization force between surface and subsurface of liquid. The surface tension of water is quite high, and the hydrogen bond between ammonia molecules is much weaker than that between water, so the ability of liquid ammonia to aggregate polar molecules through hydrophobic effect is much lower. In the early stage of life evolution, a large number of organic molecules need to be aggregated until the early life that can replicate itself appears. Water is competent in this respect, but the ability of liquid ammonia is questionable.