PART FIVE Falling Into History

       The lab hummed quietly. Desks and tables and benches were cluttered with things, the white walls crowded with graphs and posters and cut-out cartoons, all vibrating slightly under bright artificial light. Like any lab anywhere: somewhat clean, somewhat disorderly. The one window in the corner was black and reflected the interior; it was night outside. The whole building was nearly empty.

      But two men in lab coats stood at one of the benches, leaning forward to look at a computer screen. The shorter of the two tapped at the keyboard below the screen with a forefinger, and the image on the screen changed. Green corkscrews on a black field, squiggling so that they looked sharply three dimensional, as if the screen were a box. An image from an electron microscope; the field was only a few microns across.

       “You see it’s a kind of plasmid repair of the gene sequence,” the short scientist said. “Breaks in the original strands are identified. Replacement sequences are synthesized, and when these replacement sequences are introduced into the cell, the breaks are seen as attachment sites, and the replacements bind to the originals.”

       “Do you introduce them by transformation? Electroporation?”

       “Transformation. Treated cells are injected along with a competent, and the repair strands make a conjugal transfer.”

       “In vivo?”

       “In vivo.”

       A low whistle. “So you can repair any little thing? Cell division error?”

       “That’s right.”

       The two men stared at the corkscrews on the screen, waving about like the new tips of grapevines in a breeze.

       “You’ve got proof?”

       “Did Vlad show you those mice in the next room?”

       “Yeah.”

       “Those mice are fifteen years old.”

       Another whistle.

       They went next door into the mice room, muttering to each other under the hum of machinery. The tall one stared curiously into a cage, where patches of fur breathed under wood chips. When they left again they turned out the lights in both rooms. The flicker of the electron microscope screen illuminated the first lab, giving it a green cast. The scientists went to the window, talking in low voices. They looked out. The sky was purple with the coming day; stars were popping out of existence. Out on the horizon stood a black massive bulk, the flat-topped mound of an immense volcano. Olympus Mons, the largest mountain in the solar system.

       The tall scientist shook his head. “This changes everything, you know.”

       “I know.”

      From the bottom of the shaft, the sky looked like a bright pink coin. The shaft was round, a kilometer in diameter, seven kilometers deep. But from the bottom it seemed much thinner and deeper than that. Perspective plays a lot of tricks on the human eye.

      Such as that bird, flying down the round pink dot of the sky, looking so big. Except it wasn’t a bird. “Hey,” John said. The shaft director, a round-faced Japanese named Etsu Okakura, looked at him, and through their two faceplates John could see the man’s nervous grin. One of his teeth was discolored.

      Okakura looked up. “Something falling!” he said quickly, and then: “Run!”

      They turned and ran over the shaft floor. Quickly John found that although most of the loose rock had been swept off the starred black basalt, no effort had been made to make the shaft bottom perfectly level. Miniature craters and scarps became increasingly difficult as he gained speed; in this moment of primate flight the instincts formed in childhood reasserted themselves, and he kept pushing off too hard with each step, coming down on uninspected terrain with a jolt and then pushing off wildly again, a crazy run until finally he caught his toe and lost control and fell crashing across the ragged stone, arms flung out to save his faceplate. It was small comfort to see that Okakura had fallen as well. Fortunately the same gravity that had caused their tumbles was giving them more time to escape: the falling object had not yet landed. They got up and ran again, and once again Okakura fell. John glanced back and saw a bright metallic blur hit the rock, and then the sound of the impact was a solid whump, like a blow. Silver bits splashed away, some in their direction: he stopped running, scanned the air for incoming ejecta. No sound at all.

      A big hydraulic cylinder flew out of the air and banged end over end to their left, and they both jumped. He hadn’t seen it coming.

      After that, stillness. They stood nearly a minute, and then Boone stirred. He was sweating; they were in pressurized suits, but at 49°C the shaft bottom was the hottest place on Mars, and the suit’s insulation was built for cold. He made a move to help Okakura to his feet, but stopped himself; presumably the man would rather get up himself than owe giri to Boone for the help. If Boone understood the concept properly. “Let’s have a look,” he said instead.

      Okakura got up, and they walked back over the dense black basalt. The shaft had long ago been bored into solid bedrock, in fact it was now about twenty percent of the way through the lithosphere. It was stifling at the bottom, as if the suits were entirely uninsulated. Boone’s air supply was a welcome coolness in the face and lungs. Framed by the dark shaft walls, the pink sky above was very bright. Sunlight illuminated a short conic section of the shaft wall. In midsummer the sun might shine all the way – no, they were south of the Tropic of Capricorn. In shadow forever, down here.

      They approached the wreck. It had been a robot dump truck, hauling rock up the road that cut a spiral into the shaft wall. Pieces of the truck were mixed with big rough boulders, some scattered as much as a hundred meters from the point of impact. Beyond a hundred meters debris was rare; the cylinder that had flown by them must have been fired out under pressure of some kind.

      A pile of magnesium, aluminum and steel, all twisted horribly. The magnesium and aluminum had partially melted. “Do you think it fell all the way from the top?” Boone asked.

      Okakura didn’t respond. Boone glanced at him; the man was studiously avoiding his gaze. Perhaps he was frightened. Boone said, “There must have been a good thirty seconds between the time I caught sight of it and when it hit.”

      At roughly three meters per second squared, that had been more than enough time for it to reach terminal velocity. So it had hit at about two hundred kilometers per hour. Not so bad, really. On Earth it would have come down in less than half the time, and might have caught them. Hell, if he hadn’t have looked up when he had, this one might have caught them. He made a quick calculation. It had probably been about halfway up the shaft when he saw it. But at that point it could have been falling for quite some time.

      Boone slowly walked around into the gap between the shaft wall and the pile of scrap. The truck had landed on its right side, and the left side was deformed but recognizable. Okakura climbed several steps up the wreckage, then pointed at a black area behind the left front tire. John followed him up, scraped at the metal with the claw on his right glove’s forefinger. The black came away like soot. Ammonium nitrate explosion. The body of the truck was bent in there as if hammered. “A good-sized charge,” John observed.

      “Yes,”