Life here on our planet, Earth, is strictly carbon-based; and whether you’re talking about finding organic molecules on Mars or exoplanets that orbit within the habitable zone to their parent star — where liquid water can exist — astronomers are mostly interested in finding possible signs of extraterrestrial life. There are the core tenants to consider when hunting for alien life.
But here’s the catch: do all lifeforms require carbon-based molecules in order to exist? Or is it even necessary? What about silicon-based life? And would that even be possible? The answer: It could, conceivably. But looking at the odds, its quite an imagination. Here are reasons why.
Related media: What If Alien Life Was Silicon-Based?
Do You Have Some Carbon Molecules?
This is the first reason that shows up when astronomers — like the ones at the Search for Extraterrestrial Intelligence (SETI) — look out for signs of alien life: carbon-based lifeforms. It sort of makes sense to look out for something we already know about as an ingredient for life. But, what if you found silicon-based molecules on some distant planet, what does that mean? It could possibly be life, but whatever we know about what really gives rise to life being carbon-based, we cannot say with certainty.
Consider this analogy: Let’s say you want to buy a shirt, where do you think you’d most likely look, a boutique, right? But there could be other places to look for a shirt, like a garage, street vendor, or even your next door neighbor might have a few for sale; but chances are you might not be that lucky enough to buy a shirt from a restaurant. So the best bet is to go to a boutique and get the shirt you want.
“Carbon-based chemistry works great — we know what to look for,” Seth Shostak, a senior astronomer at the SETI Institute, said on the Curiosity Daily Podcast. “So maybe we can be forgiven, as it were, for looking for life that’s more like life as we know it than life as we don’t know it.”
Betting On Silicon Against Carbon
But here’s the main reason why we’re looking for carbon-based life, and liquid water and the oxygen that comes along with it: It all comes down to chemistry. Whenever scientists are considering other alternatives to carbon when it comes to life, silicon is what they place all their bet. Both elements are in the same group on the periodic table; it has a valence of four — that is, it can bond with up to four other atoms at once — just like carbon; and it can form long chains called polymers.
It seems carbon has an advantage over silicon by being incredibly small. What this means is that, it can make double bonds easily. That’s why when carbon oxidizes — when it bonds with oxygen — it becomes a simple molecule known as carbon dioxide. Each of the two double bonds is satisfied with one oxygen atom.
But when silicon oxidizes, it can only forms single bonds with four oxygen atoms which has a valence of two, therefore they look for another silicon atom to bond with, which looks for more oxygen, and before you know it, you have the monstrous molecule known as silicon dioxide — also known as sand. This all might sound like a minor difference, but it means everything for life (on Earth, at least).
So, Can Silicon Be Life?
Better yet still, that doesn’t mean a silicon-based life isn’t possible, just like the analogy of buying a shirt. In an article published on Scientific American, Raymond Dessy, a professor of chemistry at the Virginia Polytechnic Institute and State University, wrote that scientists are trying their darnedest to create silicon versions of the life-giving carbon-based molecules we know.
“Many silicon analogs of carbon compounds just cannot be formed,” Dessy writes. “Thermodynamic data confirm these analogs are often too unstable or too reactive. The complex dance of life requires interlocking chains of reactions, … and these reactions can only take place within a narrow range of temperatures and pH levels. Given such constraints, carbon can and silicon can’t.”
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Written by: Nana Kwadwo, Wed, Mar 13, 2019.