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Tetrahedral: The key to life on Earth?

It seems to me that tetrahedral bonding is responsible for life on earth. 

One might leap to the (reasonable) conclusion that I am referring to the element carbon and its ability to form sp3 bonds.  Life does depend on carbon, no doubt. But where does life exist, by and large?

Instead, I draw attention to the phase diagrams of H2O and SiO2 as a function of p and T, particularly the liquid and solid phases.  

While walking around on the Galapagos islands with my father and brother several years ago, I was struck by the evidence of prior lava flows from previous volcanic activity...there we were, confidently walking on top of a solid that was less dense than the magma (deep) beneath it that would kill us almost instantly if we were to come into contact with it.  Life was tenuously taking hold on a recently solidified lava flow...and of course leaving its imprint by changing the composition so that it could gain a still stronger hold.

I mentioned to Gene Stanley after a seminar that he gave at Northwestern that it seemed to me, from his lecture, that tetrahedral bonding should mean that the p-T phase diagrams of H2O and SiO2 must be quite similar to each other.  He smiled broadly and said "If I remove the units from each axis, I think it would not be possible or at least not easy, to know which phase diagram is which!"

We and most of the rest of land-based life exist on solid plates that are less dense than the liquid beneath them, which float our existence. When water freezes it forms a skin that protects life that is in the water beneath that skin...and also protects some life like polar bears that walk and run on that surface solid layer, again less dense than the liquid beneath it.

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