by Hal Clement
Throughout the morning, and early afternoon, the hot summer sun beat unmercifully down upon them out of a pale blue sky, reddening already painful sunburns and causing Truck MacLaurie to break out with a rash of prickly heat that had him scratching himself almost continually.
They made only a brief stop for lunch—under a low hill that offered a very poor kind of shade. They would not have stopped at all, but Candace insisted they needed to stretch their legs even if they had lost their appetites. She served them slices of processed ham on crackers, and coffee so hot that Truck wanted to know whether she had actually used the heater or had merely left it out in the sun for two or three minutes.
When they resumed their journey, they found the sun shaded by freshly-assembled clouds, which caused the big football player to mutter, “Thank God!
We’ve got the weather on our side, anyway.”
“I don’t like it,” said Candace, staring thoughtfully at the western sky ahead. The jeep was bumping its way up toward the mountains, and something in her tone caused Hal Parsons to slow down and look at her sharply.
“What is it, baby?’ he asked.
“According to meteorological tables, there has been an average of only one inch of rainfall in these hills during August,” she said. “Furthermore, there has never been a single rainfall of more than a quarter of an inch. Those clouds piling up ahead spell out heavy rain to me.”
“Speaks the climatologist,” said Parsons, concentrating on a barren, rocky patch of hillside ahead.
“Speaks a girl who’d like to know what’s going on,” Candace replied.
In the rear seat, Truck MacLaurie scratched, sweated and said nothing.
Slowly, circuitously, Parsons and Truck got the little jeep and its trailer up the roadless hillside, and set its course toward a notch in the hills ahead. It was after five o’clock when they reached the summit of the pass and could look down into the valley on the other side of the range. To all intents and purposes, it was an exact replica of the valley from which they had so painfully emerged.
“I don’t see anything,” said Truck, letting his eyes roam the panorama of scrub and sand and eroded rock that stretched out before them.
“I don’t either,” said Parsons, battling a feeling of disappointment which he knew to be absurd. There was no reason to believe that a flying object capable of detouring the mountain peak on their right would have selected such a barren piece of earth as its resting place. It could just as easily have steered past other peaks, over other valleys, until it reached a wide, fertile valley.
“Look at those clouds!” said Candace Parsons, staring not at the valley or the range of hills opposite, but at the sky above. “If we don’t get ourselves set up quick, we’ll be in for a wetting.”
“Hello!” Parsons exclaimed, following his wife’s gaze. “It does look grim—and it seems to be right overhead. Come on, Truck.”
“I’m glad we’re up here, instead of down there,” said the king-sized young gladiator, moving to help his professor with the camping gear. “Only time I ever saw clouds like that was in Colorado, when I played left guard for a junior college. We wound up with a flash flood that wiped out half the campus. I came up to Montana Mines the next year.”
“Better give the radio another run, before you break out the tents, Hal honey,” Candace Parsons suggested. “I’ll take charge of them until you get a message through.”
Even as she spoke, a large drop fell on her forehead, and the slow patter of beginning rain rustled around them. She got busy with the tents, moving swiftly, efficiently, and with surprising strength for a slim-looking woman. But her mind was on the weather that was encompassing them.
It simply couldn’t be happening—but it was. Great grey-and-white, swirling masses of cloud had boiled over to fill the heavens above them, and the fall of rain was increasing steadily. Her experience told her that these were not cloudburst formations, from which only a flash flood could be expected. Despite Truck’s concern—they looked more like the prelude to long, steady rain. Yet they were low, closing down relentlessly, making the ceiling almost invisible as they blanketed the taller peaks that rimmed the valley.
It was her husband who broke through her abstraction, saying, “Baby, come here. I got through to Stevensville. According to them, every watcher and radar post has been alerted all day. And we’re the furthest west observers to have seen that thing. They’ve only been waiting for another report to start an air-search.”
“If it landed anywhere around here,” said Candace Parsons, eyeing a sodden cigarette in disgust, “they won’t be able to get a plane over these peaks for quite a while—not even a helicopter.”
III
THE RADAR BEAMS had stopped—or had, at least, ceased to reach the Conservation Agent—before he had gone underground. The point where he had landed was not in line-of-sight range of any of their stations. Needless to say, however, their operators had not forgotten him.
The agent was not considering possible radar operators. In fact, he would not have considered them even if radar had been, to him, something produced by a machine. He was far too busy listening.
If a human being puts his ear close against a wall, or a doorjamb in a fairly large building he will pick up a remarkable variety of sounds. He will hear doors closing, windows rattling, and assorted creaks and thuds whose origin is frequently difficult or impossible to determine. The one thing he will not hear is silence.
The crust of a planet is much the same on a vastly greater scale. It is always full of vibrations, ranging from gigantic temblors—as square miles of solid rock slip against similar areas on the two sides of a fault plane—to ghostly echoes of sound and the faintest of thermal oscillations as the sun’s heat shifts from one side of a mountain to the other, and the rocks expand and contract to adjust to the new temperatures.
These waves travel, radiating from their point of origin, being refracted and reflected as they enter regions of differing density or elasticity, losing energy as they go by heating infinitesimally the rock through which they pass. They may die out entirely in random motion—heat—while still inside the body of the planet. Or a good, healthy wave-train may get all the way to the other side.
If it does so on Earth, it takes about twenty minutes. Then a fair proportion of it bounces from the low-density zone that is the bottom of the atmosphere, or the top of the lithosphere, whichever you prefer, and starts back again.
And every variation in density, or crystal structure, or elasticity, or chemical composition, has some effect on the way such waves travel. They may speed up or slow down. Transverse waves, or the transverse components of complex waves, may damp out—have you ever tried to skip rope with a stream of water?—and the compressional waves alone go through. Transverse waves, polarized in one direction, may be refracted through an interface, where the same sort of wave striking the same interface—at the same angle but polarized differently—may be reflected from it.
The important thing is that constantly varying conditions affect the waves. And that means that the waves carry information.
It is confused, of course. Temblors come from all directions, from all distances, due to many different causes, and through all sorts of rock. Interpreting them is not just a matter of sitting down to listen. One might as well tune in a dozen different radios to as many different musical programs, while sitting in the middle of a battlefield with a thunderstorm going on, and try to decide how many flutes were being used in one of the orchestras. The information is there, but selectivity and analysis are needed.
The agent was equipped for such selectivity, such analysis. His sensitive gear could detect any motion of the rock, down to thermal oscillation of the ions, at frequencies ranging from the highest a silicate group could maintain, to the lowest harmonic of a planet the size of Jupiter.
If his instruments proved inadequate, he could listen himself. But since just listening would involve the projection of a portion of his own body thro
ugh the hull and bringing it into contact with the rock, the act would put a crippling strain on his stone-like flesh, and would consume several millennia of time. He did not plan to take this alternative. Machines were built to be used. Why not use them?
His own senses reacted at electronic speed—were, in fact, electronic in nature, as were his thought patterns. The process of receiving a group of impulses, and of solving the multiple-parameter equations necessary to deduce all the facts as to their origin and transmission, called for just such a fast-acting computer as his mind, though even he took some time about it.
This, primarily, was because he was careful. A temblor originating near by would naturally have fewer unknowns worked into its waveform by the time it reached him. Therefore, it represented a simpler problem. Also, when solved, that problem provided quantities which could be fitted directly into the equations for more distant wave-sources, since their wave-trains must have come through the same rocks as they approached him.
His picture of the lithosphere around him grew gradually, therefore, and by concentric shells. He saw the layers of different sorts of rock and, far more important, the stresses playing on each layer—stresses that sometimes damped out to zero in the endless, tiny twitchings of the planet’s crust and that sometimes built up until the strength of the rocks, and the vastly greater weight of overlying materials could no longer resist them, and something gave.
He sensed the change, as trapped energy built up the temperature in a confined volume, until the rock could no longer be called solid, even though the pressure kept it from being anything that could be called liquid. He saw the magma pockets formed in this way migrate, up, down and across in the crust, like monstrous jellyfish in an incredibly viscous sea.
He saw certain points on the planet where they had reached so nearly to the surface that the weight above could no longer restrain the pressure of their dissolved gases. An explosive volcanic eruption is quite a sight, even from underneath.
His senses, through the vessel’s instruments, probed down toward the core of the world, where magma pockets were more frequent. In such pockets, held in solutions which might some day carry them to the upper crust, they would be accessible—the copper and silver and molybdenum, and other metals his people needed. They would lay diffused through the material of the planet.
Those were the things that interested him. He needed to know the forces at work down there—not in general, as a climatologist knows why Arizona is dry, but in sufficient detail to be able to predict when and where these metals would reach the upper crust and form ore bodies. The fastest electronic computers man has yet built would be a long time working out such problems, given the data. The agent was certainly no faster, and was less infallible.
He knew this to be so, and, therefore, spent much of his time checking and rechecking each step of the work. The task took all his attention, and, for the time being, he was totally indifferent to impulses originating near the surface—much less to a number of feeble ones which originated above the surface.
There was something a good deal more interesting than human reactions to claim the attention of the Conservation operative. He had, of course, confirmed long since his original impression that the ore beds of the planet had been looted. His principal job now was to decide how long the normal diastrophic and other geological processes would require to replace them.
On a purely general basis, replacement should take tens of millions of years for a planet of Earth’s size and constitution. Magma pockets would have to work their way up from the metal-rich depths to the outer crust. Then they would have to come into contact with materials which would dissolve or precipitate, as might be the case, the particular metals he sought.
The geological processes which depended so heavily on water or ammonia, in the liquid state, and concentrated the metallic compounds into ore deposits, could occur only near the surface. Of course, a magma pocket, commencing five hundred miles down, may not go upward. It may travel in any direction whatever, or not at all.
The density, the chemical composition, the melting point of the surrounding material, its ability to retain, in solution, the radioactives which may have been responsible for the pocket in the first place were all vital factors. Equally vital was the question of whether its crystalline makeup is such as to absorb or release energy as increasing temperature reorganizes it—the proximity of one or more of the vast iron-pockets, whose coreward settling contributes its share of energy. All of these things influence the path as well as the very existence of the pocket.
It would be relatively easy to predict, on a purely statistical basis, the number of ore-bodies to be formed in a given ten-million-year period. But the agent needed much more than that. When a freighter is dispatched to pick up metal at one specific point and deliver it to another, the schedule is apt to suffer, if the ship has to wait a million years for its load. Interrupted schedules are not merely nuisances. In a civilization spread throughout the core of the galaxy, none of whose member worlds are self-sufficient, they can be catastrophic.
So the agent measured carefully, and, as he did so, something a trifle queer began to appear. Impulses that did not quite fit into the orderly pattern he had deduced kept arriving—impulses of a nature he found, at first, hard to believe.
Then he remembered that the poachers had been here for quite a while before his own arrival, and an explanation lay before him. The impulses were of the sort that his own hull must have broadcast, while he was digging his present refuge. There could be only one thing which the poachers would logically have left behind them. They could have left evidence of their digging.
They had shown, he decided, a rather unusual amount of foresight for their kind, coupled with a ruthlessness which made the agent wonder whether they had even felt the radar beams that had greeted his own arrival. What the poachers had done was not a thing to do to an inhabited planet.
The out-of-place impulses were from mole robots, slowly burrowing their way into the world’s heart. Each one, as the agent patiently computed its position, course, and speed, was headed for a point where the release of a relatively minute amount of energy would swing delicately balanced forces in a particular direction. The direction was obvious enough. The poachers expected to be back for another load, and were stimulating Earth’s diastrophic forces to provide it.
This was a technique often used by legitimate metal-producers, but only on worlds that were uninhabited. Orogeny, even when stimulated in this fashion, may take half a million years to raise a section of landscape a few thousand feet. That still would not provide time to escape for beings who, without mechanical assistance, would take something like the same length of time to travel a few hundred.
From the agent’s point of view, the presence of such depth-charges meant that Earth was going to become, in a fairly short time, a writhing, buckling, seething surface of broken rock, molten lava and folding, crumpling, tilting rafts of silicate material on a fearfully disturbed sea of stress-fluid.
Such heartless behavior might prove unavoidable—since he wouldn’t be there at the time. But—what had produced those radar beams?
It revolted him that any planet with life should be treated in such a manner. Whether or not the life was currently intelligent was beside the point. Few generations were needed to transform a life-species, from something as unresponsive as the planet that had spawned them, into a species capable of understanding the internal mechanism of a star in detail, for any distinctions of that nature to carry weight. If those beams had originated from living bodies, something would have to be done about the moles.
The agent simply had not the equipment to do a thing. He could fight his little ship. He could investigate and analyze. He could communicate all the way across the galaxy, if something like the ionized layers of a planet’s atmosphere did not interfere.
But he had no mole robots on his vessel, no weapons that would penetrate rock, or even atmosphere, for any great distance. He could not
himself stand the temperatures at depths to which some of the poacher’s moles had already penetrated. Consequently, he could not follow them in his own ship, even if it were able to dig as rapidly as the robots. It was indeed a problem!
Sending for help was possible, but almost certainly useless. His patrol area was so far out near the galactic rim that any message would take several millennia to reach a point where it would do any good—and the ships which answered it would be at least three times as long in covering the distance as the radiation that summoned them.
By then most, if not all, of the robots would have reached then-designated target points. They would have shut off the fields which held their shape against the pressure of the surrounding rock. Once that protection was gone, no material substance in the universe could keep the half-ton of fissionable isotopes forming their cargoes at subcritical separation. All that energy would come out, and the little that wasn’t heat to start with soon would be.
Of course, even such amounts of energy are small in comparison with the usual supplies of a planet’s crust. But once released in carefully calculated spots and at even more carefully calculated times they would do exactly what the poachers wanted. The Conservation agent, checking the placement of the moles, could find no fault with the computations of the poachers’ geophysicist. He was in his own way an operator of genius!
He could, of course, arrange for official freighters to be on hand when the action bore fruit, and would certainly do so, as a last resort. But he must first attack the question of whether or not life was being endangered. For the first time since the beginning of his analysis, the agent directed his attention to the surface layers of the world.
Then he almost stopped again, as a new theory struck him. This planet had free oxygen in its atmosphere. Would its life, if any, be near the surface? But his hesitation was only momentary. He recalled the radar beams which were his only reason for suspecting life. They could not possibly have passed through any significant amount of rock. While his senses swept the surrounding crust, in ever-widening circles, he pondered the question of just how a living creature could endure such an environment. Think hard now, concentrate!
