Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: Zer0 on 31/10/2022 18:05:38
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I heard Carbon is Versatile.
You can make Alot of different Combinations of Molecules with it.
Isn't Silicon close to Carbon on the Periodic Table?
Can Silicon based Life really occur?
If Yes, Why haven't We seen any Fossilised Evidence of of it as Yet?
P.S. - I'm a Chemistry Dummy, so plz be Nice!
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Hi zero, you have been busy lately!. Carbon has the ability to form long catenated molecules and is unique in this respect. Silicon can form the analogue of hydrocarbons and these are known as silanes, but they are far less stable with many of them catching fire on exposure to air. There is no way silicon could emulate the massive range of carbon compounds. BC would be in a better position to comment on this-it's over 50 years since I studied inorganic chemistry.
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Silicon forms some very stable solid crystals with oxygen, and it is very hard to break these down.
- It is an old biological hypothesis that a solid crystal cannot be alive (ie move, eat, reproduce and grow)
- Unlike carbon, whose main compound with oxygen is the gas carbon dioxide (which can be broken down by photosynthesis)
I understand that silicon chains with side-groups are not as stable as carbon with those same side-groups.
- However, if there is an oxygen atom between the silicon atoms , they can form more stable compounds, a group of chemicals called silicones (with an extra "e" near the end).
Deep beneath the surface of the Earth, silicon compounds are liquid (and even carbon is liquid), so if there is any merit in that biological hypothesis, perhaps life could occur there?
- Life needs a source of energy; I imagine available energy would be very low in an environment which has a fairly uniform temperature and chemical composition (unlike the Earth's surface, where sunlight and the day/night cycle provides a ready source of available energy)
- But if this hypothetical deep life were brought to the surface (by a deep volcano, for example), it would solidify, and be unrecognisable to us as life.
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I recall a while back that I hypothesized that silicon-based life might be able to get around the "solid silicon dioxide problem" if it used fluorine in place of oxygen as an oxidizing agent. This is because, unlike silicon dioxide, silicon tetrafluoride is a gas (at least at standard temperature and pressure). This comes with the caveat that the solvent is hydrogen fluoride instead of water (water wouldn't be stable in a fluorine atmosphere). This leads to another problem: the silicone (silicon-oxygen) polymer backbone that silicon-based life might use to emulate carbon's polymer-making properties wouldn't be stable in liquid hydrogen fluoride either. Hydrogen fluoride reacts with silicon-oxygen bonds to create water and silicon tetrafluoride. So that might not work well.
Alternatively, silicon-based life might be able to get around the solid silicon dioxide problem by being fully aquatic and exhaling metabolic waste in the form of silicic acid or a silicate salt (or more properly in solution, the silicate ion). Sodium metasilicate has a solubility of 222 grams per liter at 25 degrees Celsius, whereas carbon dioxide's solubility is only 1.45 grams per liter at the same temperature. There might be other issues with using water as a solvent for silicon-based life, though. I recall hearing it said that water was incompatible with it, but can't recall the reasons.
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Hi.
Yes you have been busy @Zer0 . I'm glad you're inquisitive and your questions are perfectly sensible.
There have been good answers already.
No one has tried to present the argument from the other main starting position yet. Instead of thinking about what Silicon can or can't do compared to carbon, just consider how much of it exists. Life would probably find a way, if some system could develop that used, let's say Platinum instead of Carbon, then it may well do so.
However, there is only so much of each element in the universe. Stars start with Hydrogen and fuse that together to make Helium. They can fuse a few more things together and form some heavier elements but they really don't get too far up the periodic table. The heavier elements come from very few places (the old view was that they were only made in supernovae - but that view has now been revised).
Anyway, most of what is out there and available is Hydrogen. That's no use on it's own since it doesn't support much chemistry. However, plenty of Hydrogen is used in living organisms - most organic compounds have more Hydrogen than anything else (more atoms of Hydrogen but not necessarily more mass of Hydrogen because H is a low mass atom). The next most prevalent element is Helium - but that is inert, it doesn't react and bond to anything at all. ... We steadily move up the periodic table, with each progressively heavier element becoming more rare. What we see is that there was going to be much more Carbon in the Universe than Silicon and hence more opportunity for life to develop using Carbon (plus the elements lighter than Carbon) instead of using Silicon to form long molecules. So we could reasonably suspect that carbon based life would be the first on the scene.
If there was some life based on Carbon established then evolution suggests it will diverge and start tapping into all the natural resources and using all the niches before Silicon based life had enough time to really establish itself. Any primitive Silicon based life can't really compete with the well established and well evolved Carbon based life - so that life (the Silicon based life) ends. That is, if indeed, it ever really got to the point of developing far enough to be properly considered life in the first place. If it was just some non-living Silicon based substance that was beginning to threaten the niche of a carbon based life form then the Carbon based life is very likely to evolve to deal with the threat (i.e. long before that Silicon based substance really had the properties Biologists describe as "life").
Best Wishes.
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Thank You All for your Inputs.
Y'all have Finally ripped apart & devastated my Beliefs on the Chances of origination of Silicon based Life.
But I'm still Happey!
😊
Good to know stuff.
P.S. - Yeaa I've been buzy lurking around the nooks & corners of the Forum.
Since a few days, everything seemed Stagnant, no new OPs atall.
That smelled like a Perfect Opportunity to stir things up a bit & provide new content for Everyone & ask my Silly questions.
Hope the MODS don't call me out for stirring up a sht storm lol.
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Hydrogen.... That's no use on it's own
Since we are engaging in wild speculation (as science fiction authors have done for many decades)...
In its most general sense, the function of life is to redirect energy resources so as to produce a local decrease in entropy.
- A star (mostly Hydrogen, at least initially) has ample energy resources
- The flow of this energy can be redirected by magnetic fields (for example, magnetic fields throttle the flow of energy beneath a sunspot)
- So, hypothetically, you might have a form of life which is constructed from magnetic fields in the plasma of a star?
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Thanks Evan!
You just Blew my Mind.
P.S. - 🤯
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It's true that silicon and carbon are close on the periodic table and both have similar properties, but carbon has a unique ability to form a large variety of molecules, including the complex molecules needed for life as we know it.
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The trick of life is actually the hydrogen bond, which allows DNA to split and self-replicate. Not sure it would work in a fluoride environment as it's associated with the anomalous structure and properties of water.
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Isn't Silicon close to Carbon on the Periodic Table?
It's next to it in the table. But it's not similar enough.
Hypothetically, you might get a high temperature silicon (silicate) based life form.
I'm betting against it though.
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The nearest thing to a silicon life form is the diatomaceous plankton in the sea. While the cellular contents are conventional carbon-backbone chemistry, they are enclosed in a glass-like shell of silicon dioxide. So, with the abundance of chemicals and UV light from the sun, there may be some interesting chemistry going on between the cell contents and the glassy enclosure. It could be a step towards understanding how and where a novel life form may be found.
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Why haven't We seen any Fossilised Evidence of of (Silicon based Life) as Yet?
How do you know? We walk on silicon-based rocks all the time! We don't have any criteria for recognising any that may once have been alive.
As BC mentions above, at room temperature, silicates are solid, but 100km or so beneath our feet, they become plastic, and might show characteristics like movement, metabolism, reproduction, etc.
- Volcanic action can bring up rock samples from these depths, but we would just see it as a solid volcanic rock.
- What would limit life is the amount of available energy:
- At the surface of the Earth, we have a solar energy input of about 700W/m2
- Under the oceans, heat flow is around 0.1 W/m2 (and only 0.6 W/m2 through the crust), although there are big variations, such as at volcanoes and mid-oceanic ridges.
- This 4 orders of magnitude difference in available energy suggests that any life processes down there might be extremely slow
Perhaps we could keep our eyes out for some form of information storage: a silicate-based genetic code in rocks, which would provide the instructions for reproducing a silicate-based life form?
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While we are speculating about hot life, diamonds are brought up from about 100km down, where they are liquid.
- Gem-quality diamonds are clear, almost pure elemental carbon and seemingly low on structure
- Industrial diamonds are often black in colour, and have a more complex chemistry
- Could diamonds be the fossilised remains of deep life, "frozen" when they were carried to the surface?