So whenever the topic of extra terrestrial life comes around people always mention how they could be way more different than we could predict and rather than being carbon based they could be silicon based. My question is why silicon? What makes it possible to sustain life?
In: Biology
Like carbon, silicon has 4 electrons in its outer shell meaning it can form 4 separate chemical bonds. Very few elements can do this and if you wanna make the complex molecules that constitute biology, it helps to have a connector as good as carbon or silicon.
Think about a LEGO that has one dot on the top and one socket on the bottom. You can’t do much with that other than build a narrow tower. But if you can connect to other legos in four different places at the same time, you can build complicated stuff.
It’s more of a scifi thought experiment than it is anything grounded in actual data or observations. The premise is described in the other comment however there are A LOT of immediate pitfalls beyond “it can make 4 bonds”. Nearly everything else about silicon is grossly different from carbon that you can’t actually substitute silicon into any real molecules where you’d find carbon and get similar functioning compounds. The bond lengths are longer and weaker which is biggest limiting factor. This ends up making most of the compounds fall apart at lower temperatures or not even be stable period.
Silicon cannot make lipid chains, it cannot make the same carbon ring shapes, the list goes on. There’s an excellent video by Angela Collier on YouTube on the subject if you’d like far more examples and more technical details
Because silicon is in the same group as carbon on the periodic table and is able to form a decent number of large and complex molecules that would be required for life, there’s speculation that it might be a plausible alternate biochemistry to carbon-based life. It’s also abundant on rocky planets and asteroids (at least in our solar system) so we expect that there would be an abundance of it available for life to use on other words.
Silicon does have a lot of drawbacks though. It can’t form as wide a variety of molecules as carbon, it’s unstable in the presence of water, and in the presence of oxygen, it become silicon dioxide (aka quartz) which is just inert rock. So silicon-based life isn’t going to happen on an Earth-like planet, and may not be possible at all.
Silicon is the element on the periodic table that is most similar to carbon. They are in the same “group” (column) of the periodic table, and just one “period” (row) below it. Silicon can create the same general kinds of chemical structures and bonds. It’s also abundant in the universe, so there should be no shortage of it.
There are, however, several reasons why carbon is a lot better. Carbon dioxide is a gas at most relevant temperatures and pressures. *Silicon* dioxide is also called *sand* and is a solid at any temperature that could make use of water. Likewise, “silane” and its longer cousins, which are analogous to methane, ethane, propane, etc., are highly flammable with oxygen and highly reactive with water, whereas methane and ethane only react with water under specific conditions. Silicon is heavier than carbon as well, which adds up.
You hear it mentioned because it’s loosely plausible and, when talking about alien life, it’s easy to forget that life *might* look very different elsewhere in the universe. But ultimately, silicon is unlikely because while you can get the right kinds of bonding, the chemistry is so completely different that it’s unlikely such things could form life.
imagine trying to build something with basic shapes/building blocks. You could pick something like a pyramid, or maybe a sphere, or tetrahedron. Generally, it would be easiest to build something out of cubes. It gives the most flexibility and variety in how you can build something from the ground up and is super stable. Life on earth is built on carbon, which is sort of like a cube in how neatly it can form bonds, whereas other elements don’t form neat and convenient bonds like carbon. Silicon, however, has very similar properties to carbon. It’s like another kind of cube, and so we can expect a possibility for life to form based on silicon as well, though it’s never been observed.
Silicone can form many bonds like carbon can. Unfortunately it’s too heavy to form heavier chains and won’t produce complex life, like what these media sources insist it can. Silicone based life will always be simpler than carbon. Carbon is the magic element, it can form long complex chains that silicone is too heavy for. Complex life will be built of carbon, not silicone. Only more simple life can be silicone based, but it can and likely will exist, maybe on other planets, but we will likely find it one day. It just won’t be as complex as we, carbon based life, is.
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Silicon is very chemically similar to carbon, so if life were to develop centered around a different element silicon is the most likely candidate.
Most likely, but not necessarily particularly likely. Carbon is substantially more abundant in the universe than silicon and involved in many inorganic processes that silicon is not.
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