I think silicon based life (as opposed to silicone based life) is very unlikely for one simple reason - hydrogen bonding. Hydrogen only H-bonds with nitrogen, oxygen, and fluorine, the first two of which play a fundamental role in carbon based life. There is no H-bonding analog for silicon, and I see that as a serious problem. Water is certainly the primary marker here. Water is fundamental to carbon based life, and H-bonding is fundamental to the properties of water. Without H-bonding, life as we know it would not exist. Unless silicon based life processes water like carbon based life does, which I doubt, I don't see it happening. Anybody have any arguments for or against this theory?