Iconia: Silicon-based life

Whether or not silicon-based life exists, or can exist, depends entirely on how you define it.

There are well over 10,000 known species composed of silicon, silicates and organicsilicates. However, all the known species are DNA based lifeforms. As yet, there is no known silicon-based analogue for DNA. So if your definition of silicon-based life requires an alternative to DNA then, no, we haven't found any yet.

It's the flexibility of Carbon-based DNA to easily compact and expand that allows it to store the vast quantities of biochemical information that encodes life. Silicon atoms are bigger and have difficulty forming double and triple bonds. Complex polysilicon analogues are highly reactive in water and spontaneously decompose. This would suggest a non-water solvent as a standard environment. That's not to say they can't exist, just that if they do, then they'd be more fragile and have a far slower metabolism. In competition with Carbon-based life they would sorely lose. However, there are alternatives. Silicon-based life could be primarily symbiotic: lots of small independant cells each with a different genome. Or it could have a self-replicating genome. Or it could be acellular, existing as a single planetary organism of organosilicate soup. Or it could encode biochemical information with higher efficiency, 16 data bits instead of the 4 base pairs that DNA is limited to. Or it could have non-redundant transcription, 64 from 64 chemical transcriptions, instead of the 20 from 64 with DNA. There are many alternatives, and the building blocks are certainly there: Silane (SiH4) gas instead of methane (CH4) gas, Silicon dioxide (SiO2) instead of Carbon dioxide (CO2). It's far more likely that any silicon-based life form will be made of organosilicates, chemicals made from a mixture of Carbon and Silicon, rather than an inflexible Silicon only base.

Organosilicates, Silicates
Dimethylsilanediol (DMSD)Si(CH3)2(OH)2

It's interesting to note, the ratio of dissolved Nitrogen to Silicon is the main factor deciding whether a Silicon-structured or Carbon-structured animal dominates an environment. Higher Silicon means more Silicon structures, while higher Nitrogen means more Carbon-structures. Also, the availability of dissolved Iron affects the strength of the Silicon structure. Less dissolved Iron means a weaker Silicon structure. Silicate-structured species also remove more CO2 from the atmosphere than CaCO3-structured species do.