Originally published 27 September 1999
“Some are born great, some achieve greatness, and some have greatness thrust upon ’em,” says Shakespeare’s Malvolio, reading from Maria’s letter.
One might apply these words to the elements of which the world is made.
Oxygen is born great. Forged in the hot interior of stars, oxygen has from the first moment of its birth a promiscuous tendency to combine with other atoms. This appetite for union springs from its hunger for electrons, which it will happily share with other elements in molecular marriage.
For example, oxygen will combine with two hydrogen atoms to form water, that gushy substance so essential to life. Only a few weeks ago water was discovered in a meteorite, suggesting that wetness might be deliciously primeval.
Oxygen also throws in its lot with silicon and aluminum to form the rocks that make up the Earth’s crust. It constitutes 35 percent of our entire planet by weight, more than any other element. When gravity was pulling the Earth together out of the dust and gas of the pre-solar nebula, it was oxygen that did much of the “heavy lifting,” dragging its companion elements into planetary sphericity.
Carbon achieved greatness. Of the materials of the Earth’s surface it amounts to a mere drop in the bucket, a few hundredths of a percent. Who would have predicted 4 billion years ago that carbon would be the basis for life and intelligence, and ultimately the transformation of the planet?
Unlike oxygen, shy carbon is reticent in making alliances, contentedly inclined to mind the advice of Shakespeare’s Polonius: “Neither a borrower or a lender (of electrons) be.” It resides happily in exclusive affiliation with other carbon atoms, in unions as hard as diamond or as soft as graphite. When it does throw in its lot with other elements, the marriages are likely to be interesting.
The chemistry of no other element is as subtle and various as the alliances of carbon. Entire courses at universities — organic chemistry — consider nothing else. At the heart of every organic molecule is a carbon backbone, a chain or ring of carbon atoms that represents that element’s narcissistic affinity for its own kind.
Organic molecules tend to have low melting and boiling points, and therefore usually exist as liquids or gases at the temperatures of the Earth’s surface. Sometime more than 3 billion years ago, compounds of carbon, stewing in the soft envelope of the early Earth, found the means to self-catalyze their production — and life made its appearance on the planet.
All terrestrial life is carbon based, and life trumps the inorganic. Reluctant carbon was the tortoise to oxygen’s hare.
Silicon is carbon’s heftier cousin, residing just below it in the periodic table and sharing carbon’s chemical affinities. One might think that it would also share carbon’s subtle and prolific chemistry; indeed, some folks have speculated that other planets might harbor silicon-based life. But carbon’s lighter weight makes its compounds more reactive at the temperatures of the Earth’s surface. Silicon is heavier, and its compounds achieve the same degree of reactivity only at hot subterranean depths. At Earth’s surface they are as inert as sand.
Certainly, there’s plenty of silicon about, vastly more than carbon. About a quarter of the Earth’s surface rocks are silicon by weight. Sand is mostly silicon dioxide, and what could be cheaper and more plentiful than sand. But for all of its promise, and all of its plenty, silicon never achieved the greatness of carbon.
Until it had greatness thrust upon it.
Silicon has electrical properties that make it a wonderful substrate for computer circuits. Its ability to conduct electricity can easily be modified by adding impurities to pure silicon crystals. Silicon oxide, which forms on the surface of silicon when exposed to oxygen at high temperature — a kind of silicon “rust” — is a fine insulator. All of which makes it relatively easy to fabricate electrical circuits in silicon on a microscopic scale.
Carbon, in the form of intelligent life, extracted silicon from the rocks and helped it achieve its potential as — the silicon chip.
Of course, life has lifted other elements from obscurity. What would modern civilization be without artifacts of iron and aluminum, for example. But silicon’s rise to prominence incorporates some of the subtlety of its carbon cousin. A microcomputer chip the size of a thumbnail is more complex than, say, the Eiffel Tower or the Titanic. The day may come when silicon-based thinking machines surpass the intelligence of our own carbon-based brains.
And because silicon is less reactive than carbon, computer chips have a kind of stability, and — dare I say it? — immortality that our carbon-based brains lack. A few hundred years down the line, when computers rule the roost, clunky silicon will have trumped supple carbon, by patiently playing a waiting game and following Polonius’s other bit of advice: “To thy own self be true.”
