Last modified: 7:58 AM Saturday, 14 January 2017

Future pluperfect

In the classic Star Trek episode “Devil in the Dark,” the Enterprise receives a distress call: On a remote planetoid, miners are being killed by a creature that bursts upon them in the depths of the mine-shafts without warning and from seemingly solid rock, and burns them to death with a powerful acid. On investigation, the creature turns out to be an exotic organism called the Horta (shown in foreground in the photo below); to the eye, it is a kind of living rock that cuts passages for itself through the stone with the same acid it exuded to kill the miners, but when Spock mind-melds with it, he finds it is something more than that: It is a mother, and the silicon-intensive globules the miners have been smashing and tossing aside in trying to reach the ore they want are her eggs.

Spock reacts during a mind-meld with the Horta

“I feel your pain”: Spock reacts to the anguish of the Horta during a mind-meld.
[ Image Source ]

We also discover two fascinating facts about the Horta, one of which is germane to this article. The first is that, at the conclusion of the episode, during the series’ traditional post-climactic banter session, Spock tells Kirk and McCoy, in reply to a question about what the Horta’s mind had been like, “Refreshingly logical.”

The other is that, in lieu of carbon, the Horta’s DNA was based on silicon.

This was a particular suggestion in exobiology in which, once again, Star Trek was well ahead of its time. Only now, it would appear, are scientists beginning, thanks to the discovery that is the subject of this article, to appreciate that life need not share a common chemical template. And although this article is misleadingly headlined, and the organism it describes is terrestrial after all, and seems only to have implemented a partial substitution of arsenic for phosphorus in its DNA, biologists are now preparing to broaden their search for potential life-bearing planets to include ones with chemical profiles far different from what was previously assumed necessary to produce life.

Those of you who’ve studied much chemistry are probably calling up your mental periodic table of the elements, and realizing why arsenic might, under certain conditions, be a logical substitute for phosphorus. For those who haven’t looked at it in a while, however, here’s an old scholastic acquaintance to refresh your memory.

Periodic Table of the Elements

Periodic Table of the Elements — [ View at full size. ]
[ Image Source ]

Now, the first thing you’ll recall or note is that phosphorus (P) and arsenic (As) are in the same period (the same vertical column); this implies that they will have similar physical and chemical properties. This also applies to carbon (C) and silicon (Si). Thus, it is not unreasonable, I think, for NASA to search with particular attention for organisms in which familiar elements in terrestrial DNA are replaced by similar elements following this pattern. This is not proscriptive: Certainly other, entirely different, chemical foundations for life may exist; in a universe that is for all practical purposes infinite, virtually any elements hypothetically could combine to form life. But it does seem a good place to start.

Happy hunting, exobiologists. And remember: Don’t smash any silicon globules.

Originally published as a review of an article on exotic biology.

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