Validity of non-carbon based life

[pnaermao]

This thought has always intrigued me. You look back to the original periodic table made by Mendeleev (this is where the idea first struck me) the elements are alligned by similar chemical properties. "Gruppe" (I'm assuming Group) IV contains Carbon, Silicon, Titanium, Germanium, etc. (For the modern table it would be columns 13, 4, and elements 58,65,90,97) My question is, under what conditions would planets/planetoids/comets/other cosmic bodies be formed where any one of those elements would be a prominent one. Different star types, positions in galaxies, multiple stars, etc. I figure that if life was able to arise once on a planet, it would be able to do so on others as well, and if the main key element changes from Carbon to something else, life would then arise based on other things. I'm curious on:

A)What conditions are necessary for such bodies to be formed

B)What validity is there that life could be based off of anything other than carbon.

[5614]

B)What validity is there that life could be based off of anything other than carbon.

Scientists believe it possible for silicon based life forms to exist.

[Janus]

Scientists believe it possible for silicon based life forms to exist.

 

While there has been some speculation on the possibilty of silicon based life, I don't think that any positive conclusion of it possibility has been reached. In fact, most of the evidence points against it.

 

Example: carbon dioxide is a gas at standard temp and pressure, silicon dioxide is a solid. The same is true for other silicon based molecules. This means that silicon based molecules tend to be less reactive. In order to form life you need chemical reaction to take place.

 

A way around this is to place the molecules in a warmer enviroment, meaning you would need a hot planet for silicon life. The problem is that you also need complex molecules for life, and molecules made from silicon chains are more fragile than those made from carbon. The upshot is that the conditions needed for the molecules to be reactive enough for silicon based life to exist are too harsh to allow the formation of the complex molecules needed for life.

[bascule]

I think it would prove a rather foolhardy exercise to attempt to surmise the limits of ambiogenesis. We have one case study to work off of and that's obviously not a lot to go on

[[Tycho?]]

Its possible the silicon thing would work, but it would be tricky. Carbon can form chains pretty much as long as you want them to be, but it is much harder for silicon to do this. Hasn't been proven either way though, so its up in the air.

[pnaermao]

Janus brought up the point that for silicon reactions to take place easily enough the conditions would have to be extremely warm. But isn't it that as pressure increases, temperature increases (trying to remember back to High School science)? If this is so, what about a planet (we will assume a "rocky" planet and not gas) large enough and at the correct position to its star that it could have a normal gravity of 2,5,10, etc. (whatever would be neccessary) Gs. Underneath what ever atmosphere existed, and maybe then under water or another similar liquid, the combined effects of gravity and atmospheric, as well as water, pressure created the high enough temperatures?

Also, the point has been mentioned that chains based off of carbon are capable of being much longer than those of silicon. But chains still can be made, right? Would that then, should the possibility of life arising around silicon being true, limit this life? Something not as diverse as what has happened at Earth? Allowing only a few prominent "species" to exist? And then even at that, they remain simple. Single celled, or simple multicellular life forms; could they arise from these conditions? It need not be more intelligent than, lets say, bacteria.

[Sayonara]

There are several existing threads on this.

 

Search the forums for "silicon life".

[Ophiolite]

On the other hand, it is entirely possible that Earth life got kick started from clay templates that fostered replicating carbon based molecules.

See here: http://www.scienceforums.net/forums/showpost.php?p=120281&postcount=55