Evolution

by Stephen Baxter

  The ammonite moved with surprising grace, its upright spiral cutting through the waters. And it scanned its surroundings with wide intelligent eyes.

  The sunlit sea was crowded, translucent, full of rich plankton. Some of the creatures here — oysters, clams, many species of fish — would have been familiar to humans. But others would not: there were many ancient species of squid, the ammonite itself — and, dimly visible as shadows passing through the blue reaches of the deeper ocean — giant marine reptiles, mosasaurs and plesiosaurs, the dolphins and whales of the age.

  As the daylight gathered, more of the ammonite’s kind were rising, to hang like bells in the translucent water.

  But the ammonite spotted movement on the seabed. It descended quickly, sensory tentacles pushing out of its shell. By sight and feel it quickly determined that the scuttling, burrowing thing in the gritty sand was a crab. More arms slid out of the shell and wrapped around the crustacean, tiny hooks on each arm helping to secure their grip. The crab was pulled easily away from the soft seabed. A heavy birdlike beak protruded, and the ammonite bit through the crab’s shell, between its eyes. It injected digestive juices into the shell, and began to suck out the resulting soup.

  As particles of meat diffused in the water, more ammonites came sliding in.

  But the ammonite with the crab saw a shadow moving above, a shadow with a snout and fins, silently sliding, rapidly resolving. It was an elasmosaur; a marine reptile, a kind of plesiosaur with an immensely long neck. Abandoning its kill, the ammonite ducked into its shell. The opening in the shell was immediately sealed off with a heavy cap of hardened tissue.

  The elasmosaur fell on the ammonite, pushed its shell over, and clamped its powerful jaws around the narrowest part of the spiral. But it could not break through. After breaking a cluster of teeth, the elasmosaur dropped the shell, letting it drift back to the ocean floor. Frustration and pain seethed in its one-dimensional awareness.

  The ammonite had endured violent shaking, but it was safe in its armored home.

  But one immature ammonite had not been so wary. It tried to flee, its jets pushing it this way and that.

  The elasmosaur took its consolation kill well. Its teeth sliced expertly across the spiral shell at the place where the body was attached to the inner surface. Then it shook the shell hard until the ammonite, still alive, tumbled out into the water, naked for the first time in its life. The fish-lizard took its prize in a single gulp.

  Now the elasmosaur spotted a cloud in the water. It plunged in without hesitating.

  The cloud was a shoal of belemnites, thousands strong. The little squid had gathered for protection, and their defensive systems, of sentries and ink and shimmying, deceptive movements, were usually effective even against predators as fast as this elasmosaur. But they had been caught out by this creature’s angry lunge. They darted away, venting ink furiously at the immense invader, or even leaping out of the ocean altogether and into the comet-bright air. Still, hundreds of them died: each a pinpoint of awareness, each of them in its way unrepeatable and unique.

  Meanwhile, cautiously, the crab-killer ammonite had opened its shell once more. A tube of muscle protruded from the opening, and a high-pressure stream of water pulsed out, jetting the ammonite up and into the blue waters. It had lost the crab. But no matter. There was always another kill to make.

  So it went. It was a time of savage predation, in the sea as on land. Mollusks hunted ammonites, boring through shells, poisoning prey animals, and firing deadly darts. In response, bivalves had learned to bury themselves deep in sediment, or had evolved spines and massive shells to deter attackers. Limpets and barnacles had forsaken the deep sea, colonizing shallow environments on the shore where only the most determined of hunters could reach them.

  Meanwhile, the seas teemed with predatory reptiles. Carnivorous turtles and long-necked plesiosaurs fed on fishes and ammonites — as did pterosaurs, flying reptiles who had learned to dive for the riches of the ocean. And huge, heavy-jawed pliosaurs preyed on the predators. Measuring some twenty-five meters long, with jaws alone some three meters long, their sole stratagem to rip and shake their prey apart, the pliosaurs were the largest carnivores in the history of the planet.

  The rich Cretaceous oceans teemed, enacting a three-dimensional ballet of hunter and hunted, of life and death. It had been so for tens of millions of years. But now a bright light was building above the glimmering surface of the ocean, as if the sun were falling from the sky.

  The ammonite’s eye was drawn upwards. The ammonite was smart enough to feel something like curiosity. This was new. What could it be? Caution prevailed: Novelty usually equated to danger. Once more the ammonite began to withdraw into its shell.

  But this time even its mobile fortress could not protect it.

  The comet punched through Earth’s atmosphere in fractions of a second. It blasted away the air around it, blowing it into space, leaving a tunnel of vacuum where it had passed.

  The ammonite was trapped right under the comet’s fall. It was as if a great glowing lid closed across the sky. Its substance immediately vaporized, the ammonite died. So did the belemnites. So did the elasmosaur. So did the oysters and clams. So did the plankton.

  The ammonites had stalked the oceans of the Earth, spawning thousands of species, for more than three hundred million years. Within a year, none of them would be left alive, none. Already, in these first fractions of a second, long biographies were being abruptly terminated.

  The few dozen meters of water offered the comet nucleus no more resistance than the air. All the water flashed to steam in a hundredth of a second.

  Then the comet nucleus hit the seabed. It massed a thousand billion tons, a flying mountain of ice and dust. It took two seconds to collapse into the seabed rocks, delivering in those seconds the heat energy released by all of the Earth’s volcanoes and earthquakes in a thousand years.

  The nucleus was utterly destroyed. The seabed itself was vaporized: rock flashed to mist. A great wave pulsed outward through the bedrock. And a narrow cone of incandescent rock mist fired back along the comet’s incoming trajectory, back through the tunnel in the air dug out in the comet’s last moments. It looked like a vast searchlight beam. Around this central glowing shaft, a much broader spray of pulverized and shattered rock, amounting to hundreds of times the comet’s own mass, was blown out of the widening crater.

  In the first few seconds thousands of billions of tons of solid, molten, and vaporized rock were hurled into the sky.

  On the coastal plain of the North American inland sea, the duckbill herds gathered around the pools of standing water. They hooted mournfully as they clustered and nudged each other. Predators, from chicken-sized raptors upwards, watched stray duckbill young with cold calculation. In one place a crowd of ankylosaurs had gathered, their dusty armor glistening, like a Roman legion in formation.

  An orange glow could be seen deep in the south, like a second dawn. Then a thin, brilliant bar of light arrowed into the sky, straight as a geometrical demonstration — straighter, in fact, than a laser beam, for the beam of incandescent rock suffered no refraction as it pushed out through the hole in the Earth’s superheated air. All of this unfolded in silence, unnoticed.

  The crocodile-faced suchomimus stalked the edge of the ocean, her long claws extended. Just as she did every day, she was looking for fish. The death of her mate days before was a dull ache, slowly fading. But life went on; her diffuse grief gave her no respite from hunger.

  Elsewhere a group of stegoceras was foraging, scattered. These pachycephalosaurs were about as tall as humans. The males had huge caps of bone on their skulls, there to protect their small brains during their earth-shuddering mating competitions, when they would crash their heads together like mountain sheep. Even now two great males were battling, ramming their reinforced heads together, the bony clatter of their collisions echoing across the plains. This species had sacrificed much evolutionary potential to these contests. The n
eed to maintain such a vast protective cap of bone had limited the development of the pachycephalosaur brain for millions of years. Locked in biochemical logic, these males cared nothing for shifting lights in the sky, or the double shadows that slid across the ground.

  On this beach it was just another day in the Cretaceous. Business as usual.

  But something was coming from the south.

  By now the crater was a glowing bowl of shining, boiling impact melt, wide enough to have engulfed the Los Angeles area from Santa Barbara to Long Beach. And its depth was four times the height of Everest, its lip farther above its floor than the tracks of supersonic planes above Earth’s surface. It was a crater ninety kilometers across and thirty deep formed in minutes. But this tremendous structure was transient. Already great arching faults had opened up, and immense landslides, tens of kilometers wide, began to collapse the steep walls.

  And the seabed was flexing. The Earth’s deeper rocks had been pushed down into the mantle by the comet’s hammer blow. Now they rebounded, rising up through twenty kilometers, breaking through the melt pool to the surface. The basement rock itself, almost liquefied, quickly spread out into a vast circular structure, a mountain range forty kilometers across, erected in seconds. Meanwhile water strove to fill the pit that had been dug into the ocean floor. And already ejecta debris was falling back onto the crater’s shifting floor, a rain of burning rock. Temperatures reached thousands of degrees — enough to make the air itself burn, nitrogen combining with oxygen to form poisons that would linger for years to come. It was a chaotic battle of fire, steam, and falling rock.

  From the impact site, superheated air fled at interplanetary speeds. A great circular wind gushed out from the Yucatan, down into South America, and across the Gulf of Mexico. The shock wave was still moving at supersonic speeds ten minutes later, when it reached the coast of Texas.

  To the south of the beach, the thin pillar of light had fanned outward. It became more diffuse, and changed color, becoming a deeper orange white. Tiny flecks of orange could be seen flying up around its base. And now a band of darkness spread over the southern horizon. Still, all this unfolded in silence. What was coming was still moving much more rapidly than sound. The dinosaur herds were oblivious; still the young Pachycephalosaurs battled, locked into their Darwinian dance.

  But the birds and the pterosaurs knew the sky. A group of pterosaurs had been working the ocean, skimming low over the surface seeking to scoop up fish in their hydrodynamically elegant beaks. Now they turned and headed inland, flapping to gain speed. A flock of small, gull-like birds followed, rising up on gray-white wings that seemed to pulse in the glowing rock light.

  Of the thousands of dinosaurs, only the suchomimus reacted to the light show. She turned to the south, and her slit pupils narrowed at what she saw. Some instinct made her splash away from the water to run higher onto the shore. The warm sand was soft under her feet, slowing her down. But still the suchomimus ran.

  Two young raptors, working playfully at the shell of a stranded sea turtle, lifted their heads with speculative interest as she passed. A corner of the suchomimus’s clever mind rippled with alarm signals. She was breaking many of her innate rules; she was making herself vulnerable. But a deeper instinct told her that the stain of darkness spreading over the horizon was more of a threat than any raptor.

  She reached a bank of low dunes. A ball of fur squirmed indignantly out from beneath her feet and fled with blurring speed.

  Over the coastal plain, the light began to fade.

  At last the dinosaurs were disturbed. The great herbivore herds, the duckbills and ankylosaurs, lifted their heads from their browsing and turned to face the south.

  The fan of ascending rock was invisible now, hidden by a wall of darkness that spanned the horizon. But it was a moving wall whose front bubbled and writhed. Lightning flickered over the moving surface, making it shine purple white.

  Even now, in these last seconds, there was little sense of strangeness. It was like an eerie twilight. Some of the dinosaurs even felt drowsy, as their nervous systems reacted to the reduced level of light.

  Then, from out of the south, the shock front exploded. From silence to bedlam in a heartbeat. The front smashed the animal herds. Duckbills were hurled into the air, huge adults writhing, their lowing lost in the sudden fury. The competition among the hard-skulled stegoceras was concluded without resolution, never to be resumed. Some of the great ankylosaurs stood their ground, turning into the wind, hunkering down like armored bunkers. But the very ground was torn up around them, the vegetation ripped out and scattered; even the lakes explosively emptied of their water. The shallow dune exploded over the suchomimus, instantly burying her in gritty darkness.

  But as quickly as it had come, the shock wave passed.

  When she felt the ground’s shuddering cease, the suchomimus began to scrabble at the earth. She sneezed the grit out of her nostrils, her great translucent eyelids working to clear her eyes, and clambered to her feet.

  She stepped forward gingerly. The new ground was rubble strewn, uncertain, difficult to walk on.

  The coastal plain was unrecognizable. The dune that had sheltered her was demolished, the wind’s patient, centuries-long work erased in seconds. The plain was littered with debris: bits of pulverized rock, seabottom mud, even a few strands of seaweed and smaller sea creatures. Above her, clouds boiled, streaming north.

  Still the noise continued, great crackling shocks that rained out of the sky as sound waves folded over on themselves. But the suchomimus heard none of this. She had been deafened in the first instant of the shock’s passage, her delicate eardrums crushed.

  Dinosaurs lay everywhere.

  Even the largest duckbills had been smashed to the ground. They lay, broken and twisted, under scattered sand and mud. A group of raptors lay together, their lithe bodies tangled up. Everywhere the old lay with the young, parents alongside their children, predators with their prey, united in death. Most disasters, like floods and fires, selectively affected the weakest, the young and the old and the ill. Or else they targeted species — an epidemic, perhaps, carried by an unwitting host across a land bridge between the continents. But this time, none had been spared, none save the very fortunate, like the suchomimus.

  The suchomimus saw a silver fish. It twitched, carried a dozen kilometers in seconds, still alive. The suchomimus’s gut rumbled gently. Even now, as the world ended, she was hungry.

  But the wind’s work was not yet done. Already, over the ocean, the air was rushing back to fill the vacuum created at the impact site. It was like an immense inhalation.

  The suchomimus, toying with her fish, saw the wall of darkness bear down once more. But this time it came from inland, and it was laden with debris, with dirt and rocks and uprooted trees and even a huge male tyrannosaur that writhed lifeless, high in the air.

  Once more the suchomimus dived at the sand.

  From the furies of the crater the shock front continued to spread out, like a ripple around a fallen stone. Further inland, where Giant had raided the tyrannosaur nest, the front had wrought devastation around a great circle big enough to have been wrapped around the Moon.

  Tornadoes spun off the advancing front like willful, destructive children.

  To Giant, the twister was a tube of darkness that connected sky to ground. At its feet, what looked like splinters rose up, whirled and fell back. The giganotosaurs’ ancestors had invaded a continent. Now Giant reared up and hissed, bobbing his head, eyes triangulating on the approaching menace.

  But this was no saurian competitor. As the twister approached it grew ever larger, towering high above him.

  At last something in Giant’s mind focused on those twigs scattered at the feet of this climatic monster. Those “twigs” were trees, redwoods and ginkgoes and tree ferns, scattered as easily as pine needles.

  His brothers made the same calculation. The three of them turned and ran.

  The base of the twister tore c
asually through the blanket forest, destroying trees, scattering rock. Animals weighing five tons or more were hurled into the air, great slow-moving herbivores suddenly flying. Many of them died of shock even before they hit the ground.

  In her burrow, Purga was shaken awake by the rattling of the earth. She and her mate huddled closely around the two pups, and they listened to the howling of the wind, the clatter and crunch of trees being shattered, the scream of dying dinosaurs.

  Purga closed her eyes, baffled, terrified, longing for the noise to stop.

  And in the foothills of the Rockies, the mother azhdarchid sensed the approach of the mighty wind. Hastily she folded up her wings and waddled on wrists and knees toward her nest.

  Her young clustered around, but she had no food to give them, and they pecked at her angrily. The chicks were still flightless, their wing membranes yet to develop. For now they had only loose, useless flaps of skin trailing between their flight fingers and hind legs. And yet they were already beautiful, in their way; the scales that clustered around their thin necks, a relic of their reptilian ancestry, caught the high sunlight, gleaming and glistening.

  But now clouds raced across the sun. The twisters would not reach so high. But the shock front was still a broiling wall of turbulent air, still powerful even so far from the impact site.

  A first gust buffeted the nest. The chicks screeched and stumbled.

  Without thinking the mother flapped her wings, taking to the air. A primitive imperative had taken over. There would always be more broods, if she survived. The chicks, receding beneath her, squawked their anger and fear.

  As the wall of wind approached, there was a moment of stillness.

  The azhdarchid’s airspeed dropped. She turned and spread her wings, instinctive responses coming to play. She held out her long flight finger and her hind limb, and subtle twitches of thigh and knee adjusted the tension in her wings. She was an exquisite flying device, an apparatus of tendons, ligaments, muscle, skin and fur, shaped by tens of millions of years of evolution.