That fact had taken approximately twenty years to discover.

But what controlled the order of amino acids in the protein? The answer turned out to be DNA, the genetic-coding substance, which acted like a switching manager in a freightyard.

That particular fact had taken another twenty years to discover.

But then once the amino acids were strung together, they began to twist and coil upon themselves; the analogy became closer to a snake than a train. The manner of coiling was determined by the order of acids, and was quite specific: a protein had to be coiled in a certain way, and no other, or it failed to function.

Another ten years.

Rather odd, Leavitt thought. Hundreds of laboratories, thousands of workers throughout the world, all bent on discovering such essentially simple facts. It had all taken years and years, decades of patient effort.

And now there was this machine. The machine would not, of course, give the precise order of amino acids. But it would give a rough percentage composition: so much valine, so much arginine, so much cystine and proline and leucine. And that, in turn, would give a great deal of information.

Yet it was a shot in the dark, this machine. Because they had no reason to believe that either the rock or the green organism was composed even partially of proteins. True, every living thing on earth had at least some proteins—but that didn't mean life elsewhere had to have it.

For a moment, he tried to imagine life without proteins. It was almost impossible: on earth, proteins were part of the cell wall, and comprised all the enzymes known to man. And life without enzymes? Was that possible?

He recalled the remark of George Thompson, the British biochemist, who had called enzymes "the matchmakers of life." It was true; enzymes acted as catalysts for all chemical reactions, by providing a surface for two molecules to come together and react upon. There were hundreds of thousands, perhaps millions, of enzymes, each existing solely to aid a single chemical reaction. Without enzymes, there could be no chemical reactions.

Without chemical reactions, there could be no life.

Or could there?

It was a long-standing problem. Early in planning Wildfire, the question had been posed: How do you study a form of life totally unlike any you know? How would you even know it was alive?

This was not an academic matter. Biology, as George Wald had said, was a unique science because it could not define its subject matter. Nobody had a definition for life. Nobody knew what it was, really. The old definitions—an organism that showed ingestion, excretion, metabolism, reproduction, and so on—were worthless. One could always find exceptions.

The group had finally concluded that energy conversion was the hallmark of life. All living organisms in some way took in energy—as food, or sunlight—and converted it to another form of energy, and put it to use. (Viruses were the exception to this rule, but the group was prepared to define viruses as nonliving.)