Is the preponderance of carbon compounds due primarily to their biological origin?
Well, carbon also happens to be the fourth most abundant element in the universe...
However, considering that almost all uses for carbon (gasoline, organic acids, and the like) come from biologicals, you could say that this is somewhat the case.
Don't count on it for diamond and graphite though.
carbon is important because it can form four sigma bonds VERY stably (sp?) allowing large complex molecules (like biological ones....) to form with carbon as the backbone.
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