Evolution

by Stephen Baxter

  Though geologically sudden, the great death unfolding across the planet was not instant in the consciousness of those who endured it. For days, weeks, months, many of the doomed clung to life — even dinosaurs.

  Relatively speaking, the euoplos had been well-equipped to survive the end of the world. Their massive bulk, great strength, and heavy armor — together with a fortunate placing beneath a thick layer of cloud close to the bank of a river — had enabled a few of her kind to endure the first few horrific hours. She had survived droughts before; she ought to withstand this unexpected calamity. All she had to do was keep moving and fend off the predators.

  And so, wandering the freezing Earth, she sought food. And found hardly any.

  One by one her companions had fallen away, until the euoplo was alone.

  But, in a final irony, she had endured one last mating, from a male now dead; and she found herself heavy with eggs.

  In this new world, a land of ice and blackness and a lid of gray-black sky, the euoplo had been unable to find the ancestral rookeries. So she had constructed a nest of her own as best she could, from the bare, cinder-strewn floor of what used to be a rich forest. She had laid her eggs, lowing, setting them carefully in a neat spiral on the ground. Euoplos were not attentive mothers; six-ton tanks were not well equipped to deliver tender loving care. But the euoplo had stayed close to her nest, defending it from the predators.

  Perhaps, despite the cold, the eggs might have hatched. Perhaps some of the young could have survived the great chill; of all the dinosaurs, perhaps it was an ankylosaur who might have endured best in the new, harsher world to come.

  But the stinging rain had leached away the nutrients the euoplo’s body needed to manufacture successful eggs. Some of them had been laid with shells so thick no infant could ever break out, others were so thin they were broken as soon as she produced them. And then the rain began to damage the eggs directly, the grimy downpour etching away their protective surfaces.

  None of the eggs had hatched. The euoplo, mournful, baffled on a deep cellular level, had moved away. Immediately after she was gone, a furry cloud of mammalian predators had descended on the eggs, in their squabbling reducing the nest to a muddy battlefield.

  The last of her kind, the euoplo wandered the land, driven on by a final imperative: to survive. But the poison and the rain worked on her too. Creatures like Purga sheltered from the worst of the rain in her burrow, or under rocks — or even, once, under the scooped-out shell of a dead turtle. The euoplo was too big: There was nowhere for her to hide, and she could not burrow into the ground. So her back was ferociously scalded, and great bony plates of armor were stripped of flesh, the connecting ligaments etched and burned.

  Unthinking, she staggered toward the sea.

  Three months after the impact, Purga and Last stumbled across ground frozen as hard as rock.

  They saw few animals: Sometimes a cautious frog would watch them go by, or a bird would flee at their approach, chirping with eerie loudness, abandoning some frozen bit of offal on the ground. The relics of the lush Cretaceous vegetation, the stumps of trees and patches of undergrowth, were now frozen as hard as blackened sculptures, and any attempt to gnaw them was rewarded only with a mouthful of ice, and more often than not a chipped tooth.

  There were only two of them. Third had gone, lost to hypothermia.

  Purga longed for security, to clamber into a tree or dig into the soft earth. But there were no trees — nothing but ash and stumps and bits of roots — and the ground was too hard to burrow into. When they needed to rest they could only grub in the looser debris, making loose nests of ash and burned leaves and bits of wood, where they would lie shivering, huddled to share body warmth.

  After days of wandering, Purga and Last made their way slowly along the fringe of America’s inland ocean.

  Even here the gritty beach was frozen, and the sea itself, as charcoal gray as the sky above it, was littered with ice floes. But the gentle swell still breathed salty water over the sand. And here at the fringe of the ocean the primates found food — seaweed, small crustaceans, even stranded fish.

  The oceans, too, had been devastated by the impact. The loss of sunlight and the acid rain had massacred the photosynthetic plankton that had populated the ocean’s upper layers. With this key foundation of the ocean’s food chain gone, extinctions were following like tumbling dominoes. On wounded Earth, death stalked every realm, and the ice-littered waters of the darkened ocean hid a holocaust as horrific as that which was unfolding on the land. It would take a million years for the seas to recover.

  Purga came across a stranded starfish. Still new to ocean foraging, she had never seen such a beast before. She poked it with her snout, trying to determine which of her world categories it most closely fit: a threat, or good to eat.

  Her movements were listless. In fact she could barely see the starfish.

  Purga was weakening. She was constantly thirsty, with a nagging pain that clung to her mouth and throat and sank deep into her belly. Since the impact she had lost weight steadily, from a scrap of a body that had little excess to start with. And she was a tropical creature suddenly stranded in arctic conditions. Though her layer of fur helped trap heat, her body form was long and lanky, lacking the spherical, enclosing shape of creatures adapted to the cold. So she burned up even more energy and body mass in shivering.

  She was bony, enfeebled, continually exhausted, her thinking increasingly fuddled, her instincts dulled.

  And she was getting old. Living as vermin, the primates’ principal survival tactic had been fast breeding: there had always been simply too many of them to be eliminated by the dinosaurs’ ferocious hunting. For such creatures, there was no premium on longevity. Already Purga was coming to the end of her short, explosive life.

  Last suffered, too, of course. But, younger, she had more strength to spend. Purga was aware of a growing distance between them. It was not a question of disloyalty. This was the logic of survival. Purga sensed, deep down, that the day would come when her daughter would see her not as a foraging companion, not even as a hindrance, but as a resource. After all she had survived, maybe Purga’s final memories would be of her own daughter’s teeth at her throat.

  But now they smelled meat. And they saw more survivors, more ratlike mammals, scurrying across the beach. There was something to be had. Purga and Last struggled to follow.

  At last, her awareness flickering like a failing lightbulb, the great euoplo stumbled to the shore of the ocean.

  She looked down, uncomprehending. Water lapped at her feet, dappled by heavy raindrops. The sand was flecked with the black of soot and volcanic dust, and littered with the bones of tiny creatures. She made out the silvery bodies of fish, lifeless, their eyes pecked out by opportunistic birds. But the euoplo knew only her own weariness, hunger, thirst, loneliness, pain.

  She raised her head. The sun, setting to the southwest, was a disk, bloodred, not far above a horizon that was charcoal against charcoal.

  The euoplo stood motionless at the edge of the water. She was one of the last large dinosaurs left alive anywhere on Earth, and she stood now like a statue to her vanishing kind. Her head and tail felt very heavy, weighed down by all that armor. She let them droop. She was dying without ever having produced a single viable young. An abject misery clamored within the euoplo’s small consciousness.

  There was a sharp nip at the pad on the base of her foot.

  It was a therian mammal. It was no more prepossessing than Purga, and yet equipped with teeth that scissored — just as, one day, a lion’s would. It had run forward and bit her, with absurd boldness. The euoplo hooted her indignation. With a vast effort, she raised one immense foot. But when she slammed it down into the water she made only a splash; the scurrying mammal escaped.

  But, all around her, more survivors gathered.

  None of these animals were large. Purga and Last were here, and other mammals, little ratlike creatures that had kept themselves
alive in their underground burrows, warmed through this long winter by their constant body heat. There were birds, protected by their hot blood and small size from an event which their more spectacular relatives could not endure. Here, too, were insects, snails, frogs, salamanders, snakes, creatures who had endured in burrows and riverbanks or deep holes. These small, scurrying creatures had been used to feeding off scraps and hiding in the corners anyhow; to them, the comet impact hardly made things worse.

  Now they moved closer to this giant, the last of the monsters who had dominated their world for a hundred million years. In the long empty months since the impact, as they spread out through a world like a charnel house, many of them had learned to exploit a new food source: dinosaur flesh.

  Times had changed.

  Extinction was a terminus more drastic than death.

  At least with death there was the consolation that your descendants would go on after you, that something of your kind would linger on. Extinction took away even that comfort. Extinction was the end of your life — and of your children, and all your potential grandchildren, or any of your kind, on to the end of time; life would go on, but it would not be your kind of life.

  Dread though they were, extinctions had always been commonplace. Nature was packed thick with species, each connected to all the others through competition or cooperation, all endlessly struggling for survival. Though nobody could get permanently ahead, it was possible to fail — through bad luck, or disaster, or invasion by a better-equipped competitor — and the price of failure had always been extinction.

  But the comet impact had now triggered a mass extinction, one of the worst in this battered planet’s long history. Dying was occurring in every biological realm, on land, in the sea, and in the air. Whole families of species, whole kingdoms, were falling into the darkness. It was a huge biotic crisis.

  At such a time it didn’t matter how well adapted you were, how well you evaded the predators or competed with your neighbors, for the most basic ground rules were changing. During a mass extinction, it paid to be small, numerous, geographically widespread, to have somewhere to hide.

  And, crucially, to be able to eat other survivors in the aftermath.

  Even then survival depended as much on good fortune as good genes: not evolution, but luck. For all their smallness and ability to hide, more than half the mammals had gone extinct with the dinosaurs.

  But the mammals owned the future.

  The euoplo was not aware of her legs collapsing. But there was suddenly a damp cold under her belly, a gritty saltiness in her mouth where her head dangled into the water.

  She closed her eyes. The heavy armor made the lids opaque. She rumbled deeply — a sound that another of her kind could have heard kilometers away, had there been any to hear — and tried to spit the brine out of her mouth. She retreated into her bony armor, like a turtle inside its shell. Soon it was as if she could no longer hear the hiss of rain on the sand and water, the scuffling of the ugly little creatures who surrounded her.

  Even to the last she knew no peace, only a huge reptilian loss. But she felt little pain, when the small teeth went to work.

  This last great dinosaur was a storehouse of meat and blood that fed the squabbling horde of animals for a week.

  At the end of that time, as the acid rain began to leach the huge gnawed plates of the euoplo’s back gleaming white, Purga and Last encountered another group of primates. There were several of them, mostly about Last’s age or younger — so they had probably been born after the impact, and had known nothing, all their lives, but this straitened world. They looked lean, hungry. Determined. Two of them were male.

  They smelled strange. They were not even distantly related to Purga’s family. But they were undoubtedly Purgatorius. The males had no interest in Purga; her subtle scent told them she was too old to bear any more litters.

  Last gave her mother a final glance. And then she scampered over to the others, where the males, whiskers quivering, began to sniff her and to nuzzle her with bloodied snouts.

  After that day Purga never saw her daughter again.

  IV

  A month later Purga, wandering alone, came upon the carpet of ferns.

  Entranced, Purga hobbled forward as fast as she could. These were only lowly groundcover growths, but their fronds made a dim green shade. On the underside she could see little spore sacs, brown dots.

  Green, in a world of soot and ash gray.

  Ferns were robust survivors. Their spores were tough enough to withstand fire, small enough to be carried great distances on the wind. In some cases the new growths sprouted directly from surviving root systems, black, creeping roots that were far more indestructible than the roots of trees. In times like this, as the light slowly recovered and photosynthesis became possible, the ferns faced little competition. Amid the muddied ash and clay, the world was taking on a look it had not had since the Devonian age some four hundred million years before, when the first land plants of all — primitive ferns among them — had made their tentative colonies.

  She climbed. The tallest of these ground huggers gave her a platform just a few centimeters off the ground, but she clambered onto the fronds gratefully. It was enough to release in her a flood of inchoate memories of how she had scurried along the branches of the great, vanished Cretaceous forests.

  Later, she dug. The rain still fell, and the ground was boggy, but by digging close to the tough roots of the ferns she was able to construct a satisfactory burrow. She began to relax, for the first time since the impact — perhaps for the first time since the crazed troodon had begun to pursue her.

  Life had nothing more to ask of Purga. One of her pups had survived, and would breed, and through her the great river of genes would pass on, on into an unknowable future. And it was an irony that in former times she would surely already have succumbed to predation by now: It was the great emptying of the world that had preserved her life — a few extra months won at the expense of uncounted billions of creatures.

  As content as it was possible to be, she settled to sleep in a cocoon of earth that still smelled of the great burning that had ended a world.

  The planet was filling up with fast-breeding, short-lived creatures. Already almost all of Earth’s population had been born into the new era, and had known nothing but ash, darkness, and carrion. But as Purga slept her hind legs convulsed and her front paws scrabbled at the ground around her. For Purga, one of the last creatures on the planet to remember the dinosaurs, the terrible lizards still stalked, at least in her dreams.

  There came a morning when she did not wake, and the little burrow became her coffin.

  Soon a blanket of sediment, deposited by the ocean, covered over the vast impact crater. The great geological deformation was eventually hidden under a layer of limestone a thousand meters thick.

  Of the Devil’s Tail itself, nothing remained but traces. The nucleus had been destroyed in the first seconds of the impact event. Long before Earth’s skies cleared, the last remnants of the coma and the glorious tail — the tenuous body of the comet, now cut from its tiny head — blew away in the wind from the sun.

  But still the comet had left a kind of memorial. In the boundary clay would be found tektites — bits of Earth that had been blasted into space and returned, melted into glassy dewdrop shapes like tiny space capsules by their re-entry into the air — as well as fragments of quartz and other minerals, shocked into strange glassy configurations by the impact energy. There were shards of crystalline carbon, normally formed only deep in Earth’s interior, but baked on the surface in those few ferocious seconds: tiny diamonds, littering an ash of burned Cretaceous forests and dinosaur flesh. There were even traces of amino acids, the complex organic compounds once delivered by long-vanished comets to rocky Earth, the compounds that had enabled life to emerge here: a wistful present from a visitor who had come too late.

  And as the dust clouds finally cleared and the chill dispersed, the comet’s final gift
to the Earth came into play. Vast amounts of carbon dioxide, baked out of the limestone of the shattered seabed, now lingered in the air. A savage greenhouse effect kicked in. The vegetation, striving to recover, struggled to cope. The first millennia were times of swamps, of marshes and rotting bogs, where dead vegetation choked lakes and rivers. All over the world coal was laid down in great seams.

  At last, though, as spores and seeds blew around the world, new plant communities blossomed.

  Slowly, Earth turned green.

  Meanwhile, time worked on Purga’s tiny remains.

  Within hours of her death, blowflies had laid eggs in her eyes and mouth. Soon flesh flies were dropping larvae on her skin. As maggots burrowed into the little corpse, so the gut bacteria that had served her all her life burrowed out. Intestines burst. The contents began to rot other organs, and the cadaver liquefied, with a powerful stink, like cheese. This attracted carnivorous beetles and flies.

  In the days after her death, five hundred types of insects feasted on Purga’s corpse. Within a week, there was nothing left but her bones and teeth. Even the great DNA molecules could not survive long. Proteins broke down into their individual building blocks; amino acids in turn decayed into mirror-image forms.

  Just a few days after that, a flood of acidic water swept away the little hollow. Purga’s bones were dumped in a shallow depression half a kilometer away, jumbled with the bones of raptors, tyrannosaurs, duckbills, and even troodons: enemies made equal in the democracy of death.

  With time, more layers of mud were laid down by floods and bank-bursting rivers. Under pressure, the layers of silt turned to rock. And, in her rocky tomb, Purga’s bones were further transformed, as mineral-rich water was forced into their every pore, filling them with calcite, so they became things of rock themselves.