Evolution

by Stephen Baxter

  Near the lake itself a desolate scene greeted the giganotosaurs.

  Dinosaurs stampeded. Great herds of rival duckbill species mingled, armored beasts like ceratops and ankylosaurs jostled for room, herbivores ran alongside giant predators. There were even mammals, blinking in the light, running amidst giant feet. All the animals charged in panic, their feet burned by the smoldering ground, clattering into each other blindly. This would have been unimaginable just a couple of hours ago. The intricate ecological relationships of herbivores and carnivores, of predators and prey, built up over a hundred and fifty million years, had utterly collapsed.

  Giant pushed forward, barging his way through the panicking mob, driven to the water by a deep instinct. He plunged into the lake, ignoring the smoldering debris that floated on the surface. The deeper layers were still blessedly cool. But even with his head submerged he could see more meteors hitting the lake, creating bubble trails in the water like bullets.

  And now a missile shape rose before him, a great mouth gaped white, and through the murky water he could see rows of conical teeth. He flailed back.

  The crocodile had lain at the bottom of her lake, silent, patient.

  A distant cousin of the seagoing deinonychus, so far the events of this tumultuous day had meant little to her. She had felt the shuddering of the Earth and the responding ripple of the water, noticed the peculiar lights in the sky. But she expected to ride out this storm, as she had ridden out many before. She could stay underwater for an hour at a time, as her metabolism was capable of shutting down almost completely when necessary. Her thinking was slow, patient. She knew that all she had to do was lie here in the mud, and the storm would pass, and once more her food would come to her.

  But now a dinosaur came blundering clumsily into the water — not just skimming the fringe to drink and browse, like the stupid duckbills, but immersing itself, actually swimming in her domain. She felt anger at this intrusion, mixed with anticipation at any easy meal. She pushed herself away from the mud and rose toward the surface, which glimmered with meteor light. But more massive bodies plunged helplessly into the turbid water, struggling in the clinging mud of the lake bottom.

  She attacked, of course.

  Giant thrashed, evading the crocodile’s reaching jaws, and in his blundering he managed to land a kick on the crocodile’s snout. The crocodile backed away briefly. But soon she was returning to the attack. Giant might have withdrawn. But a crowd of animals was pushing into the water behind him. The crocodile fought and snapped at the invaders; and the animals warred amongst themselves.

  But now there was a mighty surge, as an aftershock of the comet’s seismic jolt shuddered through the basement rock. The ground was uplifted, cracked — and the water drained suddenly away, leaving Giant stranded amid drying vegetation and writhing animals.

  The crocodile, suddenly exposed to hot, dry air, could not understand what had happened. She tried to burrow into the mud, instructed by instincts that had guided her as a baby from her shell to her first swim. But the mud was hardening, drying fast; she could not even dig into the ooze.

  Still the meteors fell, lancing through the clouds of smoke like pillars of light.

  The winds and the tsunami had already wiped out most of the living things, from insects to dinosaurs, in North and South America. Around the world, the gathering fires were now killing most of those who had survived.

  But the worst was yet to come.

  The coarser ejecta at the periphery of the comet impact had fallen back quickly, much of it pounding the disturbed ground within one or two diameters of the central crater, the rest falling as forest-igniting meteors. But the great central plume of rock vapor had continued to rise, propelled by its own heat energy. In the vacuum of space, solid particles condensed out of this glowing cloud, and, still white-hot, began to fall back to Earth. But where they had risen through a tunnel of vacuum, now they fell back into atmosphere, and they dumped their energy into the air. It was a lethal hail of fire, a planetwide blanket of uncounted billions of tiny, white-hot meteors.

  All over the planet, the air began to glow.

  Purga had reached a foothill. Her mate, Third, and her one surviving pup were at her side. They could go no further toward the true Rockies, for even here the land had been broken and jumbled by the ground waves, littered with boulders that were many times Purga’s height.

  This would have to do. She began to dig into the loose dirt, seeking to build a burrow.

  She glanced back the way she had come. Under banks of billowing smoke the whole of the land glowed bright orange; it was an extraordinary sight. Even here, on this rocky rise, she could feel the heat; even here she could smell the stink of smoke and burning flesh.

  She could see the clouds that had drawn her here. They were ragged, but still clustered around the upper slopes of the mountains. Against a sky as black as night the clouds glowed orange white, reflecting the glow of the burning land. But now, beyond the clouds, that orange light from the south crept overhead. The sky itself began to glow, like a dawn erupting all over the sky, all at the same time. The color quickly escalated to orange, then yellow, then a dazzling white, sun-bright.

  The heat’s first breath reached them.

  The primates scrabbled desperately at the ground.

  On the cracked pond floor Giant was somehow on his feet, surrounded by the dead. He couldn’t breathe; his chest strained at air that was dense with smoke and bits of glowing, charred vegetation. It was like being in a gray fog. He saw nothing but smoke, dust, swirling ash.

  Heat pulsed, hot as an oven. There was a stink of burning meat.

  He felt a sharp pain in his hand. He lifted it in dim curiosity. His fingers were burning, like candles.

  His last thought was of his brothers.

  His death came in a moment of fulminant shock. He knew nothing about it: His vital organs were destroyed too quickly for his brain to process a conscious reaction. Then his muscles cooked and coagulated. They contracted his arms and legs, but his spine was extended, so that in this moment of death he adopted a posture oddly like a boxer’s, head back, hands up, legs flexed. His flesh was seared away, and the enamel on his teeth began to shatter.

  All this before Giant had time to fall to the ground.

  And then the very rocks began to crack.

  Jewel-like, its sudden brilliance reflecting from the ancient seas of its companion Moon, Earth was beautiful. But it was the beauty of a dying world.

  Half of all the heat energy released by the burning air was injected into the deeper atmosphere and the ground. All over the planet, the sky was as hot and bright as the sun. Plants and animals burned where they stood. The trees of the mighty Cretaceous forests were consumed like pine needles. Any birds in the air disappeared in a puff of flame, and the pterosaurs vanished into the maw of extinction. The burrows of mammals and insects and amphibians turned into tiny coffins. Purga’s second pup, whimpering and alone, was quickly baked.

  Purga was spared. The last clouds, shadowed black, became ragged, dispersing quickly, soon vaporized into steam — but for the crucial minutes of the great heat pulse they served to shield the ground beneath them from a sky as bright as the sun.

  It was just an hour after the impact.

  III

  After the first few days the Earth’s shuddering died away, and the daily stamping of the great mountain-reptiles was gone.

  Purga was used to darkness. But not to silence, this eerie stillness that went on and on.

  For countless generations the dinosaurs had framed the lives of Purga’s kind. Even after this cataclysmic shock, she had vague visions of arrays of dinosaurs waiting in silent rows to trap any mammal unwise enough to poke her snout out of her burrow.

  But she could not stay here, in this hasty burrow. For one thing there was nothing to eat; the family had quickly excavated and consumed any burrowing worms or beetles they could reach. They didn’t even know when it was day and when it was night. Thei
r sleep cycles had been thrown off by their flight during the day of the impact, and they found themselves waking at different hours, their hunger conflicting with their fear of the strange, cold silence above. They bickered among themselves, snapping and biting.

  And as time wore on the temperature plunged, from the intense heat of the hours of the burning sky to a bitter cold. The primates were sheltered by the thick layer of earth above them, but even that would not protect them forever.

  Finally Third turned on the pup — Last, for she was Purga’s last surviving child. Purga couldn’t see Third. But with her whiskers and well-developed hearing she could sense her mate approaching the pup, step by step, mouth wide, as if stalking a centipede.

  Third was angry, confused, frightened, and very, very hungry. But what he was doing made a certain sense. After all, there was nothing to eat here. If the flesh of the pup kept the adults alive a little longer, long enough for them to produce another litter, the genetic program would be fulfilled. The calculations were relentlessly logical.

  Perhaps in other times Purga would have submitted to Third’s aggression, even helped him finish off the pup. But Purga’s life had already been long for her kind, and she had suffered a series of extraordinary events: the destruction of her first home, her dogged pursuit by Wounding Tooth — and now the nightmare of the comet impact and her stranding in this world of cold and silence.

  The imperatives resolved themselves. She bit Third savagely on the thigh, and scrambled past him to stand alongside her daughter.

  Last was just as confused as the others. But she figured out that her mother was defending her from some kind of attack by her father. And so she stood with Purga and bared her teeth at Third. For a full half-minute the burrow was filled with hissing and the sound of tiny paws scraping the ground aggressively; three sets of whiskers filled the space between the primates, each of them waiting for the other to strike.

  In the end it was Third who backed off. He gave up quite suddenly, abandoning his aggressive posture and curling up alone in a corner of the burrow. Purga stood with her daughter until the anger and aggression had drained out of her system.

  It was this final incident that changed the balance of the forces in Purga’s mind.

  They couldn’t stay here, for they would starve, or freeze, if they didn’t kill each other first. They had to go out, regardless of what mysterious dangers lurked in the newly silent world above. Enough was enough. When her body clock next woke her, Purga pushed away the dirt that clogged the entrance to the burrow.

  And emerged into the dark.

  After two days, the fire in the sky had died. But now, from pole to pole, dust and ash covered the wounded Earth, a black shroud laced with wispy, yellow-white clouds of sulfuric acid. The Earth had been transformed from a starlike shining to a dismal, gloomy darkness, darker than the core of the comet which had wrought such devastation. Dust and ash: The dust was comet fragments, and sea-bottom dirt, and even volcanic debris spewed out after the immense seismic shocks that had rippled through the planet. And the ash was burned life, trees and mammals and divergent species of dinosaurs from America and China and Australia and Antarctica, burned to cinders by the global firestorms and then burned again in the pulse of superheat, now mingled together in the choked stratosphere. Meanwhile, sulfur, baked out of seabed rock in the first moments of the impact, had lingered in the air, forming sulfuric acid crystals. The high, bright acid clouds reflected away sunlight and drove the cold deeper still.

  Followed by Third and Last, Purga crept cautiously away from her burrow’s mouth, whiskers twitching nervously. It was late afternoon, here in the chill heart of North America. If the sky had been clear, the sun would still have been well above the horizon. There was only the gloomiest of twilights, barely sufficient even for Purga’s huge, sensitive eyes.

  She stumbled forward over bare, scorched rock. Everything was wrong. There was no scent of green growing things, nor the pungent, spicy stink of the dinosaurs, not even of their dung. Instead, she smelled only ash. The whole of the great thick green-brown layer of Cretaceous life had been burned off: even the dead leaves, even the dung, all destroyed. All that was left were minerals, lifeless dirt, and rock. It was as if Purga had been transported to the surface of the Moon.

  And it was cold, a deep intense cold that quickly penetrated through diminished layers of fat to her bones.

  She came to the ruins of what had been a small stand of tree ferns. She scraped at the ground with her claws, but the ground was strangely hard — and it was cold, deep cold, so cold it hurt the pads of her hands. But when she licked her hand, a slow trickle of water gathered in her mouth.

  Just a few days earlier this had been a place of tropical forest and swamplands. No frost had formed here in millions of years. But now there was frost. Purga scrabbled at the ground, cramming the strange, chill stuff into her mouth. Slowly she got mouthfuls of water — and plenty of ash and dirt along with it.

  She tried to dig deeper. She knew that even after the most ferocious fire there was food to be had: hardened nuts, deep-buried insects, worms. But the nuts and spores were trapped under a lid of frozen ground, too tough for Purga’s small paws.

  She moved on, feeling her way through the dark with her whiskers.

  She came to a shallow puddle. In fact it was the footprint of a vanished ankylosaur. Her snout hit a hard surface: brutally cold and hard as rock. The cold that stabbed through her fur was intense. She backed up hastily.

  Like frost, she had never encountered solid ice before either.

  More cautiously she poked at the ice with her snout and hands. She scraped and scratched — she could smell the water that was somehow hidden here, and it maddened her to be able to get no closer to it. Frustrated, she began to circle the little puddle, pushing and probing. At last she came to a place where the ankylosaur’s foot, pushing into what had been soft warm mud, had dug a somewhat deeper pit. The ice here was thin, and when she pushed at it, the surface cracked and lifted up. She jumped back, startled. The fragment of ice, upended, slid slowly into the black water. Cautiously she slid forward once more. And this time, when she tentatively dipped her snout, she found liquid water: chill, already frosting over with fresh ice, but liquid nonetheless. She sucked in great mouthfuls, ignoring the bitterness of the ash and dust that laced it.

  Attracted by the sound of her drinking, Third and Last came hurrying to her side. They quickly extended the hole she had broken, jostling to slurp up the gritty water.

  For the first time since the comet had struck, things had gotten better for Purga: not by much, but better.

  But now something touched her shoulder: something light, cold. She yelped and turned. It was a wisp of white, already melting.

  Now more flakes came drifting down out of the sky. They fell with a random, gentle movement. When a flake came close enough, she leapt up and took it in her mouth, like plucking a fly from the air. She got a mouthful of soft ice.

  It was snowing.

  Spooked at last beyond endurance, she turned and bolted for the security of the burrow.

  The impact had hurled vaporized ocean water into the air. After weeks of suspension, it began to fall back.

  There was a lot of vapor. An epochal rain fell, all over the planet.

  But the rain itself brought further devastation. It was full of sulfuric acid from the ice clouds, and the impact had injected thin clouds of toxic metals into the atmosphere, metals that now rained out. Nickel alone reached twice the threshold of toxicity for plants. Runoff water washed substances like mercury, antimony, and arsenic out of the soils, concentrating them in lakes and rivers.

  And so on. For years, every raindrop would be poisoned.

  The great rain washed out the dust and ash. All over the world, a fine layer of blackened clay was laid down, a band of darkness that would forever show up as a punctuation in the sedimentary rocks of the future — a boundary clay, one day to be studied by Joan Useb and her mother, the la
st remnant of a biosphere.

  After months of dark the sun showed, at last, through the planet-girdling layers of dust and ash. But it was only a pinprick, shedding barely any heat on the frozen land; there would be no more than a murky twilight for another year.

  The returning sun illuminated a skeletal landscape.

  Tropical plants, if not burned, had been killed by the sudden cold. Any surviving dinosaurs were succumbing to hunger and cold, their bones quickly stripped of flesh by the surviving predators. But here and there living things moved in the ash: insects like ants and cockroaches and beetles, snails, frogs, salamanders, turtles, lizards, snakes, crocodiles — creatures that had been able to hide in mud or in deep water — and many, many mammals. Their furry bodies and habits of burrowing into the shelter of the ground were protecting them from the worst of the cold. Their indiscriminate eating habits helped as well.

  It was as if the world ran with rats.

  And even now the survivors were breeding. Even now, despite the cold and the shortage of food, in the absence of their ancient predators, their numbers were increasing. Even now the blind scalpels of evolution took raw material adapted for a vanished world and cut and shaped it for the conditions of the new.

  Alone, the female euoplocephalus stumbled through the endless cold, seeking the rough forage she needed.

  She was of a species of ankylosaur. Her body was ten meters long and, before her slow starvation had begun, she had weighed as much as six tons. Her armor was bone: plates of it set in the skin of her back, neck, tail, flanks, and head. Even her eyelids were plates of bone. The plates were woven into a layer of tough ligaments, making the great carapace flexible, if heavy. Her long tail terminated in a fused mass of bone. Once she had used this club to lame a young male tyrannosaur, her greatest triumph — not that she was able to remember it; all that armor had left little room, and little need, for a large brain.