carbon-based adj.

I for one don’t doubt the possibility that some form of life might exist which had for an elemental basis some other substance than Carbon. However, during the millions of years which have elapsed since the first feeble life struggles of primitive, elemental life-stuff, there is not the slightest sign that any living thing has ever evolved with any element other than carbon as its basic substance. There must be a reason for that, and logic dictates what that reason is: Nature will not tolerate anything but the organic bases [sic] of life as we know it—the carbon base. Assuming that that base can be changed—to silicon as suggested by our distinguished colleague—would the game be worth the candle? It might be a defense against the Devil Plants—I believe it would be—but would it be a defense against Nature, the Nature that has told us what she wanted in a million year-long record—man—protoplasmic—organic—carbon-based.

Minute aquatic life feeds on the microscopic forms. Small fish, minnows, and other fry, feed on the smaller aquatic creatures. The minnows in turn supply food for larger species. It’s a chain. Destroy the first link and you destroy the whole chain. In weeks our waters will be devoid of carbon-based life in any form!

‘They aren’t carbon life at all. They're silicon life!’ Matt stared at her in disbelief. Theoretically, of course, it was quite possible. Silicon had the ability to form complex molecules very closely akin to carbon compounds. Somehow, though, he had never seriously considered life manifesting itself in anything but carbon-based protoplasm.

‘Sire,’ replied Feghoot, ‘most marvelous of all are our Ixixixangos.’ He pointed to a couple of creatures who looked like vitrified anteaters and clanked when they walked. ‘All other life-forms are either carbon or silicon based. Only the Ixixixango has a chemistry based upon both, and requires both for its substance.’

The life that we have observed—the life-as-we-know-it-on-Earth—can be defined in terms of these criteria. Carbon is the building stone, an element with a great affinity for multiple kinds of chemical combinations resulting in stable compounds. For carbon-based life, water is the solvent, and as far as we can determine it is the only solvent that could possibly fill the bill. The energy-producing chemical reaction is biochemical, an oxidation-reduction reaction which produces energy in the form of heat. Finally, carbon-based life of this sort demands an abundant supply of oxygen to allow the reaction to proceed.

Of course, we have no factual basis on which to speculate that non-carbon-based, non-water-or-colloid-based, nonprotoplasmic life does exist on Mercury any more than we can justifiably assume that it does not. We have every justification, however, in speculating that life, in order to exist, need not be life-as-we-know-it. It need not be carbon-based, it need not conform to any of the conditions required by carbon-based life-as-we-know-it here on Earth.

But once you begin with a silicon-oxygen chain, what if the silicon atom’s capacity for hooking on to two additional atoms is filled not by more oxygen atoms but by carbon atoms, with, of course, hydrogen atoms attached. Such hybrid molecules, both silicon- and carbon-based, are the ‘silicones’.

As for life as we do not know it, he speculates that it could be based on some noncarbon multivalent element, in a medium that could be gaseous or solid and, of course, on very different compounds. If we ever came across such life, he muses that we might not recognize it as living, or, if we did and it was completely different from carbon-based life, we might have to ‘revise our conception of what life is’.

As pointed out by Henderson as long ago as 1913, and by the natural theologians a century before that, carbon-based life appears to depend in a crucial way on the unique properties of the elements carbon, hydrogen, oxygen and nitrogen.

While acknowledging the possibility that these silicon-and-steel progeny might render humans, as well as other forms of carbon-based life, obsolete, the authors chose to view the situation more optimistically (no surprise since they were, after all, advocating that we begin to build these machines).

Perhaps they could get some useful information when the carbon-based polymer fabric penetrated the field.

Wes has raised my ranking by more than a dozen places and turned me into a carbon-based fighting machine.