Researcher Dirk Schulze-Makuch analyzed that carbon may not be the only basis of life. We need to have a more open vision: carbon-free living.
On Earth, carbon can form millions of compounds, while silicon is largely trapped in rocks. But elsewhere, silicon could form the basis of life.
When we look for life on other planets, what we generally mean is that we are looking for life as we understand it – life that is carbon based, requires liquid water, and uses light or chemicals as a source of energy. This makes sense when looking for life on a planet quite similar to Earth like Mars. But does this make sense for other planets, especially those outside our solar system?
A popular suggestion in science fiction is that carbon could be replaced by silicon, the key element of life. You may remember Horta from 1967 Star Trek episode “The Devil in the Darkness” or silicon life forms in the news “The Talking Stone” by Isaac Asimov.
Why does carbon dominate life on Earth?
But on Earth, Organic chemistry means carbon chemistry. This is due to carbon’s incredible versatility in forming complex and stable molecules, not only with itself but also with other elements, including hydrogen, oxygen and nitrogen. There are millions of carbon compounds, and many of them are essential to life as we know it – from proteins and DNA to methane and carbon dioxide. They are important for the metabolism of many forms of life on our planet.
Carbon-free life in space
On Earth, most rocks like granite and basalt are made of silicate minerals. (Drawing)
On Earth, replacing carbon with silicon as a component of life would not be effective. The biochemistry of our planet will not allow it. Silicon, when in free form, will be rapidly and violently oxidized to silicate (stone) when exposed to atmospheric oxygen. The same thing happens with elemental silicon exposed to liquid water. On Earth, most rocks such as granite and basalt are formed from silicate minerals, made from compounds of silicon and oxygen. Any free silicon will be bound to this oxidizing chain and will be inert, that is, incapable of combining with other elements, at moderate temperatures. Silicon will only begin to combine with other elements at very high temperatures, in magma chambers for example. But according to a paper from expert Janusz Petkowski’s team, even in this case, all the strong silicon-oxygen bonds would be broken at the same time, making them unsuitable for biological processes.
This does not mean, however, that life on Earth does not use silicon. Common algae called diatoms need silicon to grow. And without silicon, plants would not be able to maintain a strong and flexible state. Silicic acid is found in the connective tissue of hair, nails and skin. And when a bone is broken, high levels of silicon are found around the fracture as it heals.
Learn more about silicon life forms
Ironically, Earth is a planet rich in silicon. So if there’s no chance for silicon-based life on Earth, does that expose other planets to a scenario like ours? Not necessarily. The prerequisite for silicon-based life is that an exoplanet or satellite of an exoplanet does not have significant amounts of free oxygen or liquid water. In this case, organic silicon compounds may exist. In such an environment, silane (SiH4) can replace methane (CH4). So-called polysilane (a compound with several SiH4 groups) could be the start of alternative biochemistry.
What could such a world look like? Our solar system’s closest analogue is Titan, Saturn’s large moon, which is not only devoid of oxygen and liquid water, but also very cold, which would favor silicon-based life. However, life on Titan would require a different solvent than water. This moon’s methane and liquid ethane lakes could be active. But Titan contains a lot of carbon, which can outperform silicon in terms of bonding with other elements. In a world where temperatures are slightly warmer than those on Titan, methanol could serve as a possible solvent for silicon-based life.
A surprising finding from Petkowski’s article is this: sulfuric acid H2SO4 – often considered deadly – could theoretically support the rich diversity of organosilicon chemistry. There are two places in our solar system that contain a lot of sulfuric acid: the lower atmosphere of Venus and the near-surface region of the moon Io orbiting Jupiter. It may be a bit of a stretch to assume that these places are havens for life, but we must abandon our Earth-centered perspective to consider all the possibilities. Life has often surprised us in the past. And if we venture beyond the solar system, we might discover more planets and moons than we can imagine.
So far we’ve only talked about worlds orbiting stars or planets. And the planets? “orphan”, What about wandering through space without being tethered to any star system? They could use thermal energy instead of stellar radiation as their primary energy source. On Earth, sunlight supports life because there is so much light. But on a neutron star or magnetar, life can draw energy from the star’s magnetic field. Scientists Gerald Feinberg and Robert Shapiro even proposed that different arrangements of magnetic moments could be used as a mechanism to pass information from one generation to the next, much like DNA does on Earth.
So far, astronomers have only been able to detect a few organic silicon compounds in space, and carbon compounds appear to be much more abundant. Carbon could very well dominate extraterrestrial life. But there may still be a few planets where silicon-based life has developed.
Of course, if we think about future evolution, even on our own planet, the door is wide open to silicon-based life. Some definitions of life include self-replicating machines that can assemble themselves from raw materials and then transfer the assembly instructions to newly built machines, which can repeat the manufacturing process. One day, this AI “life” could dominate the fairly primitive carbon-based life forms that currently exist on Earth: us.
When searching for life on planets like Earth, a few simple assumptions help reduce the workload for astrobiologists.
One hypothesis is that the majority of life in our galaxy relies on (organic) carbon chemistry, like all life on Earth. Carbon has the unusual ability to form an incredibly large number of molecules around itself. Carbon is the fourth most common element in the universe, and the energy required to form or break carbon bonds is just enough to build molecules that are not only stable, but can also participate in chemical reactions. The fact that carbon atoms easily form bonds with other carbon atoms allows the construction of arbitrarily long and complex molecules.
The second hypothesis is the presence of liquid water because it is a ubiquitous molecule and provides an excellent environment for the formation of complex carbon-based molecules that could eventually lead to the formation of life. Some researchers envision an ammonia medium, or more likely, a water-ammonia mixture.
The third hypothesis is to focus on stars similar to the Sun. This comes from the idea of planetary habitability. Very large stars are quite short-lived, meaning that life barely has time to form on the planets orbiting them. Small stars provide very little heat and heat, so only closely orbiting planets do not freeze, and in such close orbits, planets are more likely to be “tidally locked” with the Sun. Without a thick atmosphere, one side of the planet would always be hot and the other side would always be frozen. In 2005, this question returned to the attention of the scientific community because the long lifespan of red dwarf stars could allow the formation of life on planets with thick atmospheres. This is important because red dwarf stars are extremely common.
Article source: 1thegioi
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Researcher Dirk Schulze-Makuch recently analyzed that carbon may not be the only basis of life. We need to see things more clearly:…