# Silicon Based Life



## AlexanderSen (Aug 25, 2014)

All life on Earth that we know of is all carbon based (well, mostly carbon based expect those ones made from arsenic) but there are some life on Earth which uses silica for skeletons. But silica for the most part are not common or stable enough.

Would gravity and conditions on other worlds affect the chemical reactions such as chemical bonding thus allowing for other life forms such as silicon based life?

i.e. the pressure from the gravity of a gas giant like Jupiter might produce different high pressured gases. Or different stars might have different gravitational effects on planets.

And how do we know there is an abundance of carbon on other solar systems? It is not like we actually sampled the gasses themselves. What proof do we have?

I am just wonder what is the science behind this sort of thing, if we have anymore than just assumptions.


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## chrispenycate (Aug 26, 2014)

A silicon metabolism would give some interesting problems with excretion, as the carbon dioxide equivalent is silica. Which doesn't eliminate the possibility, of course. Probably, as silicon chains tend to be more stable than carbon chains, they'd run at higher temperatures, but that's not an absolute rule. Otherwise it's assumptions, yes. (or 'interpolations', 'cause it sounds more scientific than 'guesses')

But both carbon and oxygen are on the main solar fusion chain, so they are likely to be common – and I believe organic compounds have been detected in interstellar gas clouds. So, while evidence is circumstantial, I do think carbon will be fairly widely distributed.


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## AlexanderSen (Aug 26, 2014)

I was wondering if under greater pressure from changes in gravity, or greater temperatures in heat cause a silicon excretion to be more of a liquid?


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## Mirannan (Aug 26, 2014)

chrispenycate said:


> A silicon metabolism would give some interesting problems with excretion, as the carbon dioxide equivalent is silica. Which doesn't eliminate the possibility, of course. Probably, as silicon chains tend to be more stable than carbon chains, they'd run at higher temperatures, but that's not an absolute rule. Otherwise it's assumptions, yes. (or 'interpolations', 'cause it sounds more scientific than 'guesses')
> 
> But both carbon and oxygen are on the main solar fusion chain, so they are likely to be common – and I believe organic compounds have been detected in interstellar gas clouds. So, while evidence is circumstantial, I do think carbon will be fairly widely distributed.



Silicon chains are less stable than carbon chains - AFAIK the longest such chain so far made is 4 units long. Silicone chains, however, are very stable as you say. (The difference is that silicone chains have oxygen atoms between the silicons, which makes a great deal of difference.)

That's in Earthly conditions or a bit hotter. Maybe silicon compounds would work at very low temperatures - such as those found on Titan, for example. And the energy yielding reactions might be with hydrogen rather than oxygen, leading to SiH4 as a product - which is probably liquid at that sort of temperature, and a gas at Earthly ones.

AlexanderSen - Silicon dioxide has a melting point of about 1200C. I suspect that temperatures high enough to melt it would completely destroy biological molecules based on silicon.

One more thing: Silicon based life doesn't have to work like life on Earth. Life which is essentially based on super-advanced robots (as they would look to us) with silicon based processors is possible - at least according to physical law.


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## Ray McCarthy (Aug 26, 2014)

Organic Chemistry of sufficient complexity isn't possible with Silicon, under any conditions. Even the most primitive known organisms need much more complex chemistry than is possible with Carbon or Arsenic. (Some carbon based life has arsenic, but there is no arsenic based life, only carbon).
Silicon based processors have to be designed by carbon life forms. Nor will they replicate using only naturally available materials. Computers or Robots are not alive. There is no reproduction mechanism involving natural materials.
Transistor concepts date from 1920s! it wasn't till 1947 that Germanium could be refined enough. Then later Silicon. It wasn't theory or Electronics or fabrication that delayed the parts, but being able to refine the material to unbelievable purity. Before tubes (valves) were invented there was work on semiconductors in the 19th century. The success of valves from 1905 set the chemistry back by 30+ years due to lack of investment. WWII Radar resulted in use of Germanium and Silicon mixer and detector diodes for UHF and Microwave as the earlier 1930s Telecom signals and power semiconductors (Copper Oxide and Selenium) and all valves (tubes) too slow. A few 1934 Radios did use mass produced semiconductor diodes, but the Tube/Valve diodes cheaper especially when in the same glass or metal vacuum tube sharing filament / heater of  a triode or pentode IF or AF amplifier. The French actually had a transistor working about the same time, independently of the USA Bell Labs team (1947-48). Bell beat Westinghouse purely as they ordered fresh germanium each time (each time it was purer). The "bean counters" at Westinghouse made their R&D use large WWII era stockpile in rotation. RCA was delayed also due to having less pure material.
Transistors need a staggering level of purity and also without flaws in the crystal to work. The different regions use tiny controlled amounts of especially chosen incredibly pure elements to cause a local excess or efficiency of electrons.  This is a simplified explanation. The diffusion "furnaces" to convert regions to P or N type need to be so pure and consistent that they can only be used with a single type of dopant at a very narrow range of concentration, flow, pressure and temperature.

Making Transistors and ICs (or processors) makes the idea of Alchemy seem simple! Occasionally a production line produces garbage and it's hard to understand why. The purest water, hydrofluoric acid (etching) and alcohol in the world is used in production. The lack of dust, mould, bacteria etc makes an operating theatre before use look like a municipal rubbish tip. I have some photos taken years ago in the local Analog Devices of a Semiconductor Production test facility.


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## Ray McCarthy (Aug 26, 2014)

You can tell if there are carbon compounds in a distant planet's atmosphere by spectrography.

Feel free to have non-carbon life in a story. The less you explain as to how it's possible, the more believable it is


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## Flyerman11 (Aug 28, 2014)

The problem with silicon is that it has a bond energy of 53 (silicon-silicon single bond) but the silicon - hydrogen bond is 75 and the silicon - oxygen bond is even higher - 88.

Therefore silicon will under normal circumstances (in an oxygen or hydrogen rich environment) not bond with other silicon atoms.  That is why on Earth you simply do not find simple silicon - silicon bonds. 

Carbon atoms on the other hand will readily bond with other carbon atoms since their bond energy is similar to that for carbon - hydrogen or oxygen (82, 93 and 85).  Carbon of course will also form much longer (both simple and complex) chains than any other element.


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## chrispenycate (Aug 28, 2014)

@Ray McCarthy :– spectroscopy, surely? And you will see I always hedge my bets with 'perhapses' and 'maybes' – one planet is not a sufficient sample to make absolutes. But the essential first step for life (before even reproduction) is energy, and you would need a really weird planetary situation for that to be available in electric rather than chemical form (considers trying to evolve close enough to a pulsar that the rotating magnetic force lines generate voltages and shivers). And any tetravalent atom can give you semiconductors; I remember an article in the late sixties about doped diamond transistors, that could run at far higher temperatures and voltages than either silicon or germanium (but unfortunately needed both, and didn't function at room temperature).

Not what I came to talk about. Isaac Asimov used to write a monthly science fact article in 'analog', and I remembered he did one on (or close to) this subject, so web searched it and (I hope) http://www.bigear.org/CSMO/HTML/CS09/cs09p05.htm should take you to it (grins smugly- after all, it was only 1962).


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## Ray McCarthy (Aug 28, 2014)

What ever you call it when you look at the relative levels of light in the star and reflected light of planet or the edge of disc light, or transit effect. I forget the exact word or how it's done. But it's to do with absorption or emission "lines" in the spectrum.

There are indeed semiconductors using diamond and other forms of carbon such as graphene and nanotubes. Many metal oxide + metal allow semiconductors. You can if you are careful make copper oxide diodes on copper substrate at home (you need particular temperatures etc or you get the wrong oxides) and then make a "crystal" radio.
Many compounds/alloys (Gallium Arsenide etc) work too. Though the 24GHz GaAs transistors I have I think have maximum working voltage of 2V or less.

Asimov says
"The virus, an important life form to anyone who has ever had a cold, is not."
But is he right? Or is a virus a broken off piece of life? Do any replicate without a host cell? Perhaps a Virus isn't life.

"Can we imagine life evolving to fit some other liquid, then, one perhaps not too different from water? The obvious candidate is ammonia."
On that he may be on stronger ground. He was a Chemist and published text books on Chemistry. I read one in the 1970s.

"In 1931, the spectroscope revealed that the atmosphere of Jupiter, and, to a lesser extent, of Saturn, was loaded with ammonia. "

spectrography and spectroscopy seem  to be the same thing


> Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are often used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers.


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## Mirannan (Aug 28, 2014)

Flyerman11 said:


> The problem with silicon is that it has a bond energy of 53 (silicon-silicon single bond) but the silicon - hydrogen bond is 75 and the silicon - oxygen bond is even higher - 88.
> 
> Therefore silicon will under normal circumstances (in an oxygen or hydrogen rich environment) not bond with other silicon atoms.  That is why on Earth you simply do not find simple silicon - silicon bonds.
> 
> Carbon atoms on the other hand will readily bond with other carbon atoms since their bond energy is similar to that for carbon - hydrogen or oxygen (82, 93 and 85).  Carbon of course will also form much longer (both simple and complex) chains than any other element.



Quite right. However, one compromise is a silicone (rather than silicon) chain which can be of arbitrary length - we know this because of the existence of silicone oils and rubbers. How this structure is going to form naturally is quite another matter, of course.

Another possible and fairly interesting substrate for life molecules is boron; it forms some quite large structures in combination with hydrogen (with some very unusual bonding). However, the possibility of this is limited because boron isn't all that common. It's worth noting that boron is an essential nutrient for humans, so it's actually part of Earthly life processes as well - although obviously not central in importance.


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## Ray McCarthy (Aug 29, 2014)

It's hard to see how they can occur naturally or be part of a living process. But again, in SF&F the trick is to avoid any detail or explanations.
Many Silicones are actually related to Hydrocarbons. Many have Carbon. The first synthesised (1900 or 1901) used repeating chunks of  C6H5

However I found this
http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry


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## Vertigo (Aug 30, 2014)

It's not just how they can form naturally but how they can form naturally _and_ be robust enough to compete with carbon life forms. And with carbon being around 7 times more common than silicon (within our galaxy) I just can't see silicon based life succeeding. (And boron doesn't even make into the top ten elements).


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## Ray McCarthy (Aug 30, 2014)

Ironically Silicon is massively more common on Earth than Carbon. Of course the Temperature, Water, etc may suit Carbon life very well. Hence the "Goldilocks" hypothesis for planets.


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## Vertigo (Aug 30, 2014)

That's interesting. Where's all that excess carbon then? I see that even in the solar system carbon is far more common than silicon whereas on Earth it's the other way around. Is all the carbon locked up in stars or something?


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## Ray McCarthy (Aug 30, 2014)

Some places have Methane atmospheres.
Jupiter is 2.5x mass of all the rest of Solar system apart from our sun.  Approximately 318 x Earth mass!

Carbon beats Silicon there:

```
89.8±2.0%     hydrogen (H2)
10.2±2.0%     helium (He)
≈ 0.3%     methane (CH4)
≈ 0.026%     ammonia (NH3)
≈ 0.003%     hydrogen deuteride (HD)
0.0006%     ethane (C2H6)
0.0004%     water (H2O)
```

Saturn is 95 x Earth mass

```
Composition 	
≈ 96% 	hydrogen (H2)
≈ 3% 	helium (He)
≈ 0.4% 	methane (CH4)
≈ 0.01% 	ammonia (NH3)
≈ 0.01% 	hydrogen deuteride (HD)
0.0007% 	ethane (C2H6)
```
Again far more Carbon than Silicon.

Our Sun is about 333,000 × Earth mass

```
Photospheric composition (by mass)
Hydrogen 	73.46%[11]
Helium 	24.85%
Oxygen 	0.77%
Carbon 	0.29%
Iron 	0.16%
Neon 	0.12%
Nitrogen 	0.09%
Silicon 	0.07%
Magnesium 	0.05%
Sulphur 	0.04%
```
About four times the Carbon as Silicon? I think the Hydrogen / Helium ratio is a guide to how long it's been "lit". We won't like it when it switches from "burning" (fusion) Hydrogen to Helium (but likely that's not very soon and too simplistic a view)

But likely most rocky planets with iron core (for magnetism for protection of life) are higher proportion Silicon than Carbon. Stars and Gas Giants will have more Carbon than Silicon)
Everything seems to start with Hydrogen. 
Carbon is 6
Silicon is 14
So you'd expect Stars and Gas Giants to have more Carbon than Silicon.


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## Vertigo (Aug 30, 2014)

Yes that makes sense that the rocky planets would be higher proportion silicon. Ultimately I guess that answers the original question carbon life beats silicon even when there's more silicon around.


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## Ray McCarthy (Aug 30, 2014)

I'd love if we made contact with Sentient Aliens before I die 
But finding ANY evidence of life someplace else would be lovely. It's hard to be a sample of one!


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## Vertigo (Aug 30, 2014)

I agree completely. Isn't that always the problem? We have an almost infinite universe but so far have only the one example of life in the form of terrestrial DNA. Surely there must be more out there but... that is really just hope. And with only the one example we can only use that as the basis for our speculation. And since all terrestrial DNA is related we really do only have one single example of life.

I too would love to witness the discovery of other life. That would have to be the most profound discovery possible in human experience. Except maybe the discovery of God.


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## Ray McCarthy (Aug 31, 2014)

But is all Terrestrial DNA really related, or are some identical starting points inevitable?


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## Vertigo (Aug 31, 2014)

Again, my knowledge here is very limited and is largely based on good old BBC documentaries, but I saw a series of documentaries some years ago about the cell and in them that is exactly what they were saying; all DNA on the planet that has so far been studied share a significant amount of genes which suggests a single original source. That's not to say there weren't other genesis events; it's quite possible there were but which were then unsuccessful in competition and died out. Or - the _much_ more scary thought - that there was only ever one single instance of genesis, one single moment in time when a stably self-reproducing chemical cell first appeared. And all life has descended from that single cell, that single event. At first that might seem like a ridiculously silly idea, but when you come to look at it closely you realise the other idea that several separate genesis events occurred is far more unlikely. In such a case what are the chances that the exact same combinations of chemicals that make up genes (that's some pretty complex chemicals there) appear in both life forms?

Also, if there was only one ever single instance of genesis and we can't find any other evidence of life in our solar system then the odds fall rather sharply on alien life. I'm not saying they go to zero but they do suddenly look much smaller.


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## AlexanderSen (Aug 31, 2014)

I wonder about sentient life, as it might be very simple life organisms such an algae type organism which we might take for granted. For it to be considered a life form it must be able to gather food/resources from the environment and self replicate. But my thoughts so far feel that silicon based life forms might react much slower such as plants or slow metabolism creatures. If so then what is a proper measure of time for such creatures? They might take much longer to change that carbon based life forms.


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## Ray McCarthy (Aug 31, 2014)

Speed of action has no effect on definitions of life or intelligence. Obviously we would be like may flies to a creature that takes a year to utter one word, or 100 years to have breakfast. But there is obviously a risk we might mistake a VERY slow sentient creature for a plant or rock till we notice the context (tools & structures would give pause for thought, an inhabited city might at first seem abandoned to us.)

Water bears seem to be able to have a very slow metabolism as do some animals hibernating. Some trees live 1000s of years, but very unlikely to be sentient. It seems unlikely that algae, bacteria etc could be sentient. But we don't know what surprises there may be elsewhere also we have no idea why we (and seemingly Elephants, Crows etc) are intelligent and self aware. Crows make dolphins seem a bit dumb, so obviously it's not just about brain size. I think the common rook in UK has now been shown to be as smart as the Caledonian Crow, but simply doesn't need to "use tools" creatively in the wild. Or else like Gary Larsen's cows, only does it when we are not looking. So far the smallest creative tool user found appears to be the crow. It's no wonder it's in so many myth and legends.


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## Vertigo (Aug 31, 2014)

Some say that for 'sentient' life it must be able to make decisions about its existence, gathering resources and such like but I think the generally held idea of sentience is self awareness which is far less common.

As to metabolism, I'm not sure that silicon based life would necessarily be slower than carbon based. You'd need a biochemist to speculate on the kind of reactions that would have to be involved and whether they would be slower than the reactions in involved with carbon life. And even then there is huge variation with some very fast high metabolism carbon based animals that live very short high speed lives and others that have much slower metabolisms, like sloths for example. And then in the plant world some plants, particularly in very low rainfall environments, that grow and reproduce in incredibly short time periods after rare rainfall and others, often in similar environments or very cold ones, that develop incredibly slowly and live exceptionally long lives. Without knowing the 'bio'chemistry my guess would be that, just like carbon, silicon life would have both slow and fast examples.


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