Evolution (15 page)

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.

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.

Buried deep, Purga began a spectacular journey lasting millions of years. As continents collided, the land was uplifted, bearing all its entombed passengers like some vast ocean liner riding a swell. Heat and compressing forces fractured and twisted the rocks. But erosion continued, a relentless, destructive force balancing Earth’s creative uplift. Eventually this land became an angular landscape of plateaus, mountains, and desert basins.

At last the erosion cut through the mass grave that had swallowed Purga’s bones. As the rock crumbled away bits of fossil bone emerged into the light, corpses bobbing to the surface, waking from a sixty-five-million-year slumber.

Almost all of Purga’s bones were lost, flashing to dust in geological instants, all that patient chthonic preservation wasted. But in 2010 a remote descendant of Purga’s would pick out a blackened shard in a wall of gray rock, just beneath a strange layer of dark clay, and recognize it for what it was, a tiny tooth.

But that moment lay far in the future.

Texas, North America. Circa 63 million years before present.

Through the endless forest, Plesi climbed.

Squirrel-like, she scampered up a scaly trunk and along a fat branch. Though it was close to noon, the light was dappled, uncertain. The canopy was high above her, the floor lost in green layers far below. The forest was silent save for the rustling of leaves in the warm breeze and the call of the canopy birds, those colorful cousins of the vanished dinosaurs.

It was a world forest. And it belonged to the mammals— including the primates, like Plesi.

She glanced back along her branch. There were her two pups— both daughters— who she thought of as Strong and Weak. About half Plesi’s size, they clung to the angle of branch and tree. Even now, Strong was pushing Weak subtly aside. In some species the runtish Weak might have been allowed to die. But Plesi’s kind bore few young, and in an uncertain and dangerous world, all of them had to be cared for.

But Plesi could not protect her pups forever. They were both weaned now. Though they had learned to seek out the fruit and insects that inhabited this, their birth tree, they must learn to be more adventurous— to move out into the forest, to seek out their own food.

And to do that, they had to learn to jump.

Hesitantly, scrambling at the scaly surface of the branch, Plesi tensed, and leapt.

Plesi was a plesiadapid: she belonged, in fact, to a species that would one day be called carpolestid. Plesi closely resembled her remote grandmother, Purga. Like Purga, she looked something like a small squirrel, with a low-slung body like a large rat’s, and a bushy tail. Though a true primate, Plesi retained Purga’s claws rather than nails, her eyes did not face forward, and her brain was little developed. She still even had the big night-vision eyes that had served Purga so well in the time of the dinosaurs.

The most significant development of primate bodies since Purga’s time was in the teeth; Plesi’s was a species adapted to husk fruit, as would be the possums of Australia, much later. It was a necessary response, if the primates were to find something to eat. Few animals of this time fed off leaves. In an equable world where tropical or paratropical forests spread far from the equator, there was little seasonal variation, and here in Texas the trees did not shed their leaves regularly. In fact, the trees loaded their leaves with toxins and chemicals to make them bitter or poisonous to curious mammalian tongues.

But still, since Purga, there had been little innovation in the primate line— even across two million years. It was the same for many other lineages. Long after the great impact, it was as if the emptied world had been shocked into stasis.

Plesi landed on her target branch without difficulty.

Her two pups were still huddled hesitantly against the tree trunk, and they made the mewling calls of babies. But, though the calls tugged at her, Plesi only raised her head and twitched her snout. She tried to encourage the pups to follow her by nibbling the fruit that clustered on this new tree.

At last the pups reacted. To Plesi’s surprise it was the little one, Weak, who came forward first. She scampered to the end of the branch— nervous, hesitant, but showing good balance. She raised her tail and tensed her muscles— she backed off nervously, preened the fur of her face— and then, at last, she jumped.

She overjudged slightly. She came tumbling out of the air and collided with her mother, making Plesi hiss in protest. But her agile hands and feet soon gripped the lumpy bark, and she was safe. Trembling, Weak scampered to her mother and buried her face in her belly, seeking a nipple that was now dry. Plesi let her suckle, rewarding her with comfort.

But now there was a blur of movement from the other tree. Strong, left behind, suddenly lunged forward, her immature feet slipping on the bark. And— without looking carefully, without trying to use her innate skills to estimate the distance— she leapt into the air.

Fear prickled inside Plesi.

Strong made the branch, but she landed too hard. Immediately she slid backwards. For a heartbeat she hung there, her small hands scrabbling uselessly at the bark, her hind legs waving. And then she fell.

Plesi saw her tumble in the air, wriggling, her white underbelly exposed, her hands and feet clutching at nothing. Even now Strong made the peeping cry of a lost infant. Then she fell into the leaves, and in a moment she was gone, taken by the green below, which swallowed all the forest’s dead.

Plesi clung to her branch, shuddering. It had happened so quickly. One young lost, one runtish weakling left. It was not to be borne. She hissed her defiance into the menacing green.

And, leaving Weak clinging piteously to the trunk of the tree, Plesi began to descend, down toward the green, down to the ground.

At last she reached the lower story of branches, and looked down into an oasis of light.

This was one of the endless forest’s few clearings. Within the last few months, an ancient canopy tree had fallen, eaten from within, wrecked by a random lightning strike. When it had crashed down it had cut a swath through the dense foliage. This clearing would not last long. But for now the plants of the undergrowth, like those hardy survivors, the ground ferns, were taking the opportunity to germinate, and the forest floor here was unusually lush and green. And already saplings were sprouting, beginning a ruthless vegetable race to steal the light and plug that hole in the canopy.

The forest was an oddly static place. The great canopy trees competed with each other to trap as much sunlight as they could. In the gloom of the lower levels, the light was too weak to support growth, and the floor was customarily littered by dead vegetable matter and the bones of any animals or birds unlucky enough to fall. But under the silent ground, seeds and spores abided— waiting centuries, even millennia if necessary, until the day came when chance opened up a gap in the canopy, and the race to live could begin.