Silicon-Based Alien Life

[snafupants]

Is silicon the second most probable predicate for alien life based on its chemical composition? Why might silicon be nearly or more probable than carbon?

The bolded part in the second quote might be a few strikes against silicon. The Hollywood depiction of aliens, though, seems far afield of accepted science and probability.

It's like, we don't know, so make some shit up and put big eyes on it.

Carbon forms the key component for all known naturally occurring life on Earth. Complex molecules are made up of carbon bonded with other elements, especially oxygen, hydrogen and nitrogen, and carbon is able to bond with all of these because of its four valence electrons. Carbon is abundant on earth. It is also light weight and the atom is relatively small in size, making it easier for enzymes to manipulate carbon molecules. It is often assumed in astrobiology that if life exists somewhere else in the universe, it will also be carbon based. This assumption is referred to by critics as carbon chauvinism.

The two most important characteristics of carbon as a basis for the chemistry of life, are that it has four valence bonds and that the energy required to make or break a bond is just at an appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long complex molecules and polymers.

There are not many other elements which even appear to be promising candidates for supporting life - for example, processes such as metabolism - but the most frequently suggested alternative is silicon. This is in the same group in the Periodic Table of elements and therefore also has four valence bonds. It also bonds to itself, but generally in the form of crystal lattices rather than long chains. Silicon compounds are generally stable but do not support the ability readily to re-combine in different permutations in a manner that would plausibly support lifelike processes.

Silicon has been a theme of non-carbon-based-life since it also has 4 bonding sites and is just below carbon on the periodic table of the elements. This means silicon is very similar to carbon in its chemical characteristics. In cinematic and literary science fiction, when man-made machines cross from nonliving to living, this new form would be an example of non-carbon-based life. Since the advent of the microprocessor in the late 1960s, these machines are often classed as "silicon-based life". Another example of "silicon based life" is the episode "The Devil in the Dark" from Star Trek: The Original Series, where a living rock creature's biochemistry is based on silicon.

 

[snafupants]

Obviously there are other facets to consider, such as proximity to a star or black hole as well as atmospheric things, but what are your opinions on the carbon/silicon part?

 

[The Introvert]

Silicon is also larger than Carbon.

More than twice as large, actually.

When creating the building blocks to life, I would imagine that smaller is always better - easier to create, less junk to work with, etc.

Larger is almost always more unstable.

 

[TheScornedReflex]

A silicon based life form is plausible. Especially when you take in the size of the universe and the sheer diversity of the elemental make up within.

 

[Cognisant]

In cinematic and literary science fiction, when man-made machines cross from nonliving to living, this new form would be an example of non-carbon-based life. Since the advent of the microprocessor in the late 1960s, these machines are often classed as "silicon-based life".

That seems likely, though I don't think "silicon-based" is quite the right way to describe it.

If robots could reproduce and alter the design of their offspring by some kind of genetic analogue they wouldn't need us anymore, they could breed and evolve "naturally", even if the manner in which they reproduce and transfer their artificial genes is wholly unnatural.

It wouldn't surprise me at all if the universe is teeming with artificial life.

 

[Nick]

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry Touches on many different types of life there could be.

My favorite is Methane based life.

 

[Architect]

I would have guessed that Carbon forms larger molecules easier than silicon due to its bonding sites but apparently it has a similar chemical composition

The two most important characteristics of carbon as a basis for the chemistry of life, are that it has four valence bonds and that the energy required to make or break a bond is just at an appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of arbitrarily long complex molecules and polymers. ...

Silicon has been a theme of non-carbon-based-life since it also has 4 bonding sites and is just below carbon on the periodic table of the elements. This means silicon is very similar to carbon in its chemical characteristics.

Life on a silica planet wouldn't have fossil fuels, a huge gift for technological development.

 

[BigApplePi]

Life on a silica planet wouldn't have fossil fuels, a huge gift for technological development.

Silica fossil fuels aren't possible or just unlikely?

 

[Architect]

Silica fossil fuels aren't possible or just unlikely?

Aren't possible AFAIK. Carbon can form polymers and all sorts of fantastic and useful compounds, including Graphene. Stick in the ground for a few millennia with enough pressure and heat and you get oil, tar and natural gas out.

 

[Agent Intellect]

Because of silicon's larger size, it creates weaker bonds. It also has the d-orbitals t hat carbon doesn't have (hence it can break the octet rule). These may be an issue.

One more cosmological theory I've heard is that the universe is currently in the "carbon age" meaning that, at the age the universe is in (and due to creation of elements in the cores of stars) carbon is abundant enough that it is much more likely for life to emerge as carbon based at this point in the history of the universe than any other element. In other words, the silicon age of life creation might not happen for another few billions years, when it just so happens that silicon is the element of abundance.

 

[MichiganJFrog]

The Hollywood depiction of aliens, though, seems far afield of accepted science and probability.

It's like, we don't know, so make some shit up and put big eyes on it.

The thing I always wondered about the aliens in Alien is, if they bleed acid, couldn't you just throw some baking soda on them?

 

[snafupants]

The thing I always wondered about the aliens in Alien is, if they bleed acid, couldn't you just throw some baking soda on them?

Where's the movie in that idea?

 

[joal0503]

i suppose if that changes somewhere down the line as agent intellect mentions...yea it would make more sense. but currently theres more carbon, and carbon does the job.

but even so, silicon based organics arent nearly as good for 'life'. And while I realize "life" at this point could be something I cant even dream of, Life as we know it certainly works best using carbon, and not silicon. Silicon bonds with oxygen? you get rocks, not organic life. How this happens? I have no fucking clue, but thats chemistry.

 

[Pathosray]

I don't even see why the universe would even have to resort to Silicon based life forms when Carbon is available in exceedingly greater quantities...

 

[scorpiomover]

Is silicon the second most probable predicate for alien life based on its chemical composition? Why might silicon be nearly or more probable than carbon?

The advantage of Carbon is in the flexibility of organic molecules, that is, molecules composed mostly of Carbon, Hydrogen and Oxygen. It has been assumed by many, that the reason for the high number of organic molecules, is because Carbon has the potential for 4 bonds, more than any other in its row in the Periodic table. Silicon is right below it, and also has the potential for 4 bonds. Hence the presumption that Silicon could form as many types of molecules, and consequently, life.

It's like, we don't know, so make some shit up and put big eyes on it.

Welcome to "how the world REALLY works".

 

[MichiganJFrog]

Where's the movie in that idea?

It would be meta-fiction, like when Bugs Bunny took a big spray bottle and squirted water into the dragon's mouth, or like Monty Python and the Holy Grail, both of them ridiculing tales of heroic knights and all that rot. I'm thinking something like Red Dwarf.