The Light of Other Days

part 3: THE LIGHT OF OTHER DAYS Chapter 28 - THE AGES OF SISYPHUS
As two apledons, disembodied WormCam viewpoints, Bobby and David soared over southern Africa.

It was the year 2082. Four decades had elapsed since the death of Hiram Patterson. And Kate, Bobby's wife of thirty-five years, was dead.

A year after he had accepted that brutal truth, it was never far from Bobby's thoughts, no matter what wonderful scenery the WormCam brought him. But he was still alive, and he must live on; he forced himself to look outward, to study Africa.

Today the plains of his most ancient of continents were covered with a rectangular gridwork of fields. Here and there buildings were clustered, neat plastic huts, and machines toiled, autonomous cultivators looking like overgrown beetles, their solar-cell carapaces glinting. People moved slowly through the fields. They all wore loose white clothes, broad-brimmed hats and gaudy layers of sunblock.

In one farmyard, neatly swept, a group of children played. They looked clean, well dressed and well fed, running noisily, bright pebbles on this immense tabletop landscape. But Bobby had seen few children today, and this rare handful seemed precious, cherished.

And, as he watched more closely, he saw how their movements were complex and tightly coordinated, as if they could tell without delay or ambiguity what the others were thinking. As, perhaps, they could. For he was told-there were children being born now with wormholes in their heads, linked into the spreading group minds of the Joined even before they left the womb.

It made Bobby shudder. He knew his body was responding to the eerie thought, abandoned in the facility that was still called the Wormworks-though, forty years after the death of Hiram, the facility was now owned by a trust representing a consortium of museums and universities.

So much time had elapsed since that climactic day, the day of Hiram's death at the Wormworks-and yet it was all vivid in Bobby's mind, as if his memory were itself a WormCam, his mind locked to the past. And it was now a past that contained all that was left of Kate, dead a year ago of cancer, her every action embedded in unchangeable history, like all the nameless billions who had preceded her to the grave.

Poor Hiram, he thought- All he ever wanted to do was make money. Now, with Hiram long dead, his company was gone, his fortune impounded. And yet, by accident, he changed the world...  David, an invisible presence here with him, had been silent for a long time. Bobby cut in empathy subroutines to glimpse David's viewpoint.

...The glowing fields evaporated, to be replaced by a desolate, arid landscape in which a few stunted trees struggled to survive.

Under the flat, garish sunlight a line of women worked their way slowly across the land. Each bore an immense plastic container on her head, containing a great weight of brackish water. They were stick-thin, dressed in rags, their backs rigid.

One woman led a child by the hand. It seemed obvious that the wretched child-naked, a thing of bones and papery skin-was in the grip of advanced malnutrition or perhaps even AIDS: what they used to call here, Bobby remembered with grim humor, the slims disease.

He said gently, "Why look into the past, David? Things are better now."

"But this was the world we made," David said bitterly. His voice sounded as if he were just a few meters away from Bobby in some warm, comfortable room, rather than floating in this disregarded emptiness. "No wonder the kids think we old folk are a bunch of savages. It was an Africa of AIDS and malnutrition and drought and malaria and staph infections and dengue fever and endless futile wars, an Africa drenched in savagery... But," he said, "it was an Africa with elephants."

"There are still elephants," Bobby said. And that was true: a handful of animals in the zoos, their seed and eggs flown back and forth in a bid to maintain viable populations. There were even zygotes, of elephants and many other endangered or otherwise lost species, frozen in their liquid nitrogen tanks in the unchanging shadows of a lunar south pole crater-perhaps the last refuge of life from Earth if it proved, after all, impossible to deflect the Wormwood.

So there were still elephants. But none in Africa: no trace of them save the bones occasionally unearthed by the robot farmers, bones sometimes showing teeth marks left by desperate humans. In Bobby's lifetime, they had all gone to extinction: the elephant, the lion, the bear- even man's closest relatives, the chimps and gorillas and apes. Now, outside the homes and zoos and collections and labs, there was no large mammal on the planet, none save man.

But what was done was done.

With an effort of will Bobby grasped his brother's viewpoint and rose straight upward.

As they ascended in space and time the shining fields were restored. The children dwindled to invisibility and the farmland shrank to a patchwork of detail, obscured by mist and cloud.

And then, as Earth receded, the bulbous shape of Africa itself, schoolbook-familiar, swam into Bobby's view.

Farther to die west, over the Atlantic, a solid layer of clouds lay across the ocean's curving skin, corrugated in neat gray-white rows. As the turning planet bore Africa toward the shadow of night, Bobby could see equatorial thunderheads spreading hundreds of kilometers toward the land, probing purple fingers of darkness.

But even from this vantage Bobby could make out the handiwork of man.

There was a depression far out in the ocean, a great cappuccino swirl of white clouds over blue ocean. But this was no natural system; it had a regularity and stability that belied its scale. The new weather management functions were, slowly, reducing the severity of the storm systems that still raged across the planet, especially around the battered Pacific Rim.

To the south of the old continent Bobby could clearly see the great curtain-ships working their way through the atmosphere, the conducting sheets they bore shimmering like dragonfly wings as they cleansed the air and restored its long-depleted ozone. And off the western coast pale masses followed the line of the shore for hundreds of kilometers: reefs built up rapidly by the new breed of engineered coral, laboring to fix excess carbon-and to provide a new sanctuary for the endangered communities of plants and animals which had once inhabited the world's natural reefs, long destroyed by pollution, overfishing and storms.

Everywhere, people were working, repairing, building.

The land, too, had changed. The continent was almost cloud free, its broad land gray-brown, the green of life suppressed by mist. The great northern mass which had been the Sahara was broken by a fine tracery of blue white. Already, along the banks of the new canals, the glow of green was starting to spread. Here and there he could see the glittering jewel-like forms of PowerPipe plants, the realization of Hiram's last dream, drawing heat from the core of Earth itself-the energy bounty, free and clean, which had largely enabled the planet's stabilizing and transformation. It was a remarkable view, its scale and regularity stunning; David said it reminded him of nothing so much as the old dreams of Mars, the dying desert world restored by intelligence.

The human race, it seemed, had gotten smart just in time to save itself. But it had been a difficult adolescence.

Even as the human population had continued to swell, climatic changes had devastated much of the world's food and water supply, with the desertification of the great grain regions of the U.S. and Asia, the drowning of many productive lowland farming areas by rising sea levels, and the pollution of aquifers and the acidification or drying of freshwater lakes. Soon the problem of excess population went into reverse as drought, disease and starvation culled communities across the planet. It was a crash only in relative terms; most of Earth's population had survived. But as usual the most vulnerable-the very old and the very young-had paid the price.

Overnight, the world had become middle-aged.

New generations had emerged into a world that was, recovering, still crowded with aging survivors. And the young-scattered, cherished, WormCam-linked-regarded their elders with increasing intolerance, indifference and mistrust.

In the schools, the children of the WormCam made academic studies of the era in which their parents and grandparents had grown up: an incomprehensible, taboo-ridden pre-WormCam age only a few decades in the past in which liars and cheats had prospered, and crime was out of control, and people killed each other over lies and myths, and in which the world had been systematically trashed through willful carelessness, greed, and an utter lack of sympathy for others or foresight regarding the future.

And meanwhile, to the old, the young were a bunch of incomprehensible savages with a private language and about as much modesty as a tribe of chimpanzees...

But the generational conflict was not the full story. It seemed to Bobby that a more significant rift was opening up.

The mass minds were still, Bobby supposed, in their infancy, and they were far outnumbered by the Unjoined older generations-but already their insights, folded down into the human world, were having a dramatic effect.

The new superminds were beginning to rise to the greatest of challenges: challenges which demanded at once the best of human intellect and the suppression of humanity's worst divisiveness and selfishness. The modification and control of the world's climate, for example, was, because of the intrinsically chaotic nature of the global weather systems, a problem that had once seemed intractable. But it was a problem that was now being solved.

The new generations of maturing Joined were already shaping the future. It would be a failure in which, many feared, democracy would seem irrelevant, and in which even the consolation of religion would not seem important; for the Joined believed-with some justification- that they could even banish death.

Perhaps it would not even be a human future at all.

It was wonderful, awe-inspiring, terrifying. Bobby knew that he was privileged to be alive at such a moment, for surely such a great explosion of mind would not come again.

But it was also true that he-and David and the rest of their generation, the last of the Unjoined-had come to feel more and more isolated on the planet that had borne them.

He knew this shining future was not for him. And- a year after Kate's death, the illness that had suddenly taken her from him-the present held no interest. What remained for him, as for David, was the past.

And the past was what he and David had decided to explore, as far and as fast as they could, two old fools who didn't matter to anybody else anyhow.

He felt a pressure-diffuse, almost intangible, yet summoning. It was as if his hand were being squeezed. "David?"

"Are you ready?"

Bobby let a comer of his mind linger in his remote body, just for a second; shadowy limbs formed around him, and be took a deep breath, squeezed his hands into fists, relaxed again. "Let's do it."

Now Bobby's viewpoint began to fall from the African sky, down toward the southern coast- And as he fell, day and night began to flap across the patient face of the continent, centuries falling away like leaves from an autumn tree.

A hundred thousand years deep, they paused. Bobby and David hovered like two fireflies before a face: heavy-browed, flat-nosed, clear-eyed, female.

Not quite human.

Behind her, a small family group-powerfully built adults, children like baby gorillas-were working at a fire they had built on his ancient beach. Beyond them was a low cliff, and the sky above was a crisp, deep blue; perhaps this was a winter's day.

The brothers sank deeper.

The details, the family group, the powder-blue sky, winked out of existence. The Neanderthal grandmother herself blurred, becoming expressionless, as one generation was laid over another, too fast for the eye to follow. The landscape became a grayish outline, centuries of weather and seasonal growth passing with each second.

The multiple-ancestor face flowed and changed. Half a million years deep her forehead lowered, her eye socket ridges growing more prominent, her chin receding, her teeth and jaws pronounced. Perhaps this face was now apelike, Bobby thought. But those eyes remained curious, intelligent.

Now her skin tone changed in great slow washes, dark to tight to dark.

"Homo Erectus" David said. "A toolmaker. Migrated around the planet. We're still falling. A hundred thousand years every few seconds, good God. But so little changes!..."

The next transition came suddenly. The brow sank lower, the face grew longer-though the brain of this remote grandmother, much smaller than a modern human's, was nevertheless larger than a chimpanzee's.

"Homo Habilis," said David- "Or perhaps this is Australopithecus. The evolutionary lines are tangled. We're already two million years deep."

The anthropological labels scarcely mattered. It was profoundly disturbing, Bobby found, to gaze at this flickering multigeneration face, the face of a chimpanzee-like creature he might not have looked at twice in some zoo .,. and to know that this was hi? ancestor, the mother of his grandmothers, in an unbroken line of descent. Maybe this was how the Victorians felt when Darwin got back from the Galapagos, he thought.

Now the last vestiges of humanity were being shed, the brain pan shrinking further, those eyes growing cloudy, puzzled.

The background, blurred by the passage of the years, became greener. Perhaps there were forests covering Africa, this deep in time. And still the ancestor diminished, her face, fixed in the glare of the WormCam viewpoint, becoming more elemental, those eyes larger, more timid. Now she reminded Bobby more of a tarsier, or a lemur.

But yet those forward-facing eyes, set in a flat face, still held a poignant memory, or promise.

David impulsively slowed their descent, and brought them fleetingly to a halt some forty million years deep.

The shrewlike face of the ancestor peered out at Bobby, eyes wide and nervous. Behind her was a background of leaves, branches. On a plain beyond, dimly glimpsed through green light, there was a herd of what looked like rhinoceros-but with huge, misshapen heads, each fitted with six horns. The herd moved slowly, massive, tails flicking, browsing on low bushes, and reaching up to the dangling branches of trees. Herbivores, then. A young straggler was being stalked by a group of what looked like horses-but these "horses," with prominent teeth and tense, watchful motions, appeared to be predators.

David said, "The first great heyday of the mammals. Forests all over the planet; the grasslands have all but disappeared. And so have the modem fauna: there are no fully-evolved horses, rhinos, pigs, cattle, cats, dogs..."

The grandmother's head flicked from side to side, nervously, every few seconds, even as she chewed on fruit and leaves. Bobby wondered what predators might loom out of this strange sky to target an unwary primate.

With Bobby's unspoken consent, David released the moment, and they fell away once more. The background blurred into a blue-green wash, and the ancestor's face flowed, growing smaller, her eyes wider and habitually black. Perhaps she had become nocturnal.

Bobby glimpsed vegetation, thick and green, much of it unfamiliar. And yet now the land seemed strangely empty: no giant herbivores, no pursuing carnivores crossed the empty stage beyond his ancestor's thin-cheeked, shadowed, huge-eyed face. The world was like a city deserted by humans, he thought, with the tiny creatures, the rats and mice and voles burrowing among the huge ruins.

But now the forests began to shrink back, melting away like summer mist. Soon the land became skeletal, a plain marked by broken stumps of trees that must once have risen tall.

Ice gathered suddenly, to lie in thick swaths across the land. Bobby sensed life drawing out of this world like a slow tide.

And then clouds came, immersing the world in darkness. Rain, dimly glimpsed, began to leap from the darkened ground. Great heaps of bones assembled from the mud, and flesh gathered over them in gray lumps.

"Acid rain," murmured David.

Light flared, dazzling, overwhelming.

It was not the light of day, but of a fire that seemed to span the landscape. The fire's violence was huge, startling, terrifying.

But it drew back.

Under a leaden sky, the fires began to collapse into isolated blazes that dwindled further, each licking flame restoring the greenery of another leafy branch. The fire drew at last into tight, glowing pellets that leapt into the sky, and the fleeing sparks merged into a cloud of shooting stars under a black sky.

Now the thick black clouds drew back like a curtain. A great wind passed, restoring smashed branches to the trees, gently ushering flocks of flying creatures to the branches. And on the horizon a fan of light was gathering, growing pink and white, at last turning into a beacon beam of brilliance pointing directly up into the sky.

It was a column of molten rock.

The column collapsed into an orange glow. And, like a second dawn, a glowing, diffuse mass rose above the horizon, a long, glowing tail spreading across half the sky in a great flamboyant curve. Masked by the daylight, brilliant in the night, the comet receded, day by day, drawing its cargo of destruction back into the depths of the Solar System.

The brothers paused in a suddenly restored world, a world of richness and peace.

The ancestor was a wide-eyed, frightened creature that lingered above ground, perhaps incautiously trapped there.

Beyond her, Bobby glimpsed what appeared to be the shore of an inland sea. Lush jungles lapped the swampy lowlands along the coast, and a broad river decanted from distant blue mountains. The broad ridged backs of what must be crocodiles sliced through the river's sluggish, muddy waters. This was a land thick with life- unfamiliar in detail, and yet not so unlike the forests of his own youth.

But the sky was not a true blue-more a subtle violet, he thought; even the shapes of the clouds, scattered overhead, seemed wrong. Perhaps the very air was different here, so deep in time.

A herd of homed creatures moved along the swampy coast, looking something like rhinos. But their movements were strange, almost birdlike, as, lumbering, they mingled, browsed, nested, fought, preened. And there was a herd of what looked at first glance like ostriches- walking upright, with bobbing heads, nervous movements and startled, suspicious glances.

In the trees Bobby glimpsed a huge shadow, moving slowly, as if tracking the giant plant-eaters. Perhaps this was a carnivore-even, he thought with a thrill, a raptor.

All around the dinosaur herds, clouds of insects hovered.

"We're privileged," David said. "We've a relatively good view of the wildlife. The dinosaur age has been a disappointment for the time tourists. Like Africa, it turns out to be huge and baffling and dusty and mostly empty. It stretches, after all. over hundreds of millions of years."

"But," Bobby said dryly, "it was kind of disappointing to discover that T. rex was after all just a scavenger... All this beauty, David, and no mind to appreciate it. Was it waiting for us all this time?"

"Ah, yes, the unseen beauty. "Were the beautiful volute and cone shells of the Eocene epoch and the gracefully sculpted ammonites of the Secondary period created that man might ages afterward admire them in his cabinet?" Darwin, in the Origin of Species."

"So he didn't know either."

"I suppose not. This is an ancient place, Bobby- You can see it: an antique community that has evolved together, across hundreds of millions of years. And yet."

"And yet it would all disappear, when the Cretaceous Wormwood did its damage."

"The Earth is nothing but a vast graveyard, Bobby. And, as we dive deeper into the past, those bones are rising again to confront us... ."

"Not quite. We have the birds."

"The birds, yes. Rather a beautiful end to this particular evolutionary subplot, don't you think? Let's hope we turn out so well. Let's go on."

"Yes."

So they plunged once more, dropping safely through the dinosaurs" Mesozoic summer, two hundred million years deep.

Ancient jungles swept in a meaningless green wash across Bobby's view, framing "the timid, mindless eyes of millions of generations of ancestors, breeding, hoping, dying.

The greenery abruptly cleared, revealing a flat dusty plain, an empty sky.

The denuded land was a desert, baked hard and flat beneath a high, harsh sun, the sands uniformly reddish in color. Even the hills had shifted and flowed, so deep was time.

The ancestor here was a small reptile-like creature who nibbled busily on what looked like the remains of a baby rat. She was on the fringe of a scrubby forest, of stunted ferns and conifers, that bordered a straggling river.

Something like an iguana scampered nearby, flashing rows of sharp teeth. Perhaps that was the mother of all the dinosaurs, Bobby mused. And, beyond the trees,

Bobby made out what looked like warthogs, grubbing in the mud close to the sluggish water.

David grunted. "Lystrosaurs" he said. "Luckiest creatures who ever lived. The only large animal to survive the extinction event."

Bobby was confused. "You mean the dinosaur-killer comet?"

"No," David said grimly. "I mean another, the one we must soon pass through, two hundred and fifty million years deep. The worst of them all..."

So that was why the great lush jungle panorama of the dinosaurs had drawn back. Once again, the Earth was emptying itself of life. Bobby felt a profound sense of dread.

They descended once more.

At last the final, stunted trees shuddered back into their buried seeds, and the last greenery-struggling weeds and shrubs-shriveled and died. A scorched land began to reconstitute itself, a place of burned-out stumps and fallen branches and, here and there, heaped-up bones. The rocks, increasingly exposed by the receding tide of life, became powerfully red.

"It's like Mars."

"And for the same reason," David said grimly. "Mars has no life to speak of; and, in life's absence, its sediments have rusted: slowly burning, subject to erosion and wind, killing heat and cold. And so Earth, as we approach this greatest of the deaths, was the same: all but lifeless, the rocks eroding away."

And all through this, a chain of tiny ancestors clung to life, subsisting in muddy hollows at the fringes of inland seas that had almost-but not quite-dried to bowls of lethal Martian dust.

Earth in this era was very different, David said. Tectonic drift had brought all of the continents into a single giant assemblage, the largest landmass in the history of the planet. The tropical areas were dominated by immense deserts, white the high latitudes were scoured by glaciation. In the continental interior the climate swung wildly between killing heat and dry freezing.

And this already fragile world was hit by a further calamity; a great excess of carbon dioxide, which choked animals and added greenhouse heating to an already near-lethal climate.

"Animal life in particular suffered: almost knocked back to the level of pond life. But for us it's nearly over, Bobby; the excess CO, is drawing back into where it came from: deep sea traps and a great outpouring of flood basalts in Siberia, gases brought up from Earth's interior to poison its surface. And soon that monstrous  world continent will break up.

"Just remember this: life survived. In fact, our ancestors survived. Fix on that. If not, we wouldn't be here." As Bobby studied the flickering mix of reptile and rodent features that centered in his vision, he found that idea cold comfort They moved beyond the extinction pulse into the deeper past.

The recovering Earth seemed a very different place. There was no sign of mountains, and the ancestors clung to life at the margins of enormous, shallow inland seas that washed back and forth with the ages. And, slowly, after millions of years, as the choking gases drew back into the ground, green returned to planet Earth.

The ancestor had become a low-slung, waddling creature, covered with short dun fur. But as the generations - fluttered past, her jaw lengthened, her skull morphing back, and at last she seemed to lose her teeth, leaving a mouth covered with a hard, beaklike material. Now the fur shrank away and the snout lengthened further, and the ancestor became a creature indistinguishable, to Bobby's untrained eye, from a lizard.

He realized, in fact, that he was approaching so great a depth in time that the great families of land animals- the turtles, the mammals and the lizards, crocodiles and birds-were merging back into the mother group, the reptiles.

Then, more than three hundred and fifty million years deep, the ancestor morphed again. Her head became blunter, her limbs shorter and stubbier, her body more streamlined. Perhaps she was amphibian now. At last those stubby limbs became mere lobed fins that melted into her body.

"Life is retreating from the land," David said. "The last of the invertebrates, probably a scorpion, is crawling back into the sea. On land, the plants will soon lose their leaves, and will no longer be upright. And after that the only form of life left on land will be simple encrusting forms..."

Suddenly Bobby was immersed, carried by his retreating grandmother into a shallow sea.

The water was crowded. There was a coral reef below, stretching into the milky blue distance. It was littered with what "looked like giant long-stemmed flowers, through which a bewildering variety of shelled creatures cruised, looking for food. He recognized nautiloids, what looked like a giant ammonite.

The ancestor was a small, knifelike, unremarkable fish, one of a school which darted to and fro, their movements as complex and nervous as those of any modem species.

In the distance a shark cruised, its silhouette unmistakable, even over this length of time. The fish school, wary of the shark, darted away, and Bobby felt a pulse of empathy for his ancestors.

They accelerated once more: four hundred million years deep, four hundred and fifty.

There was a flurry of evolutionary experimentation, as varieties of bony armor fluttered over the ancestors" sleek bodies, some of them appearing to last little more than a few generations, as if these primitive fish had lost the knack of a successful body plan. It was clear to Bobby that life was a gathering of information and complexity, information stored in the very structures of living things-information won painfully, over millions of generations, at the cost of pain and death, and now, in this reversed view, being shed almost carelessly.

...And then, in an instant, the ugly primeval fish disappeared. David slowed the descent again.

There were no fish in this antique sea. The ancestor was no more than a pale wormlike animal, cowering in a seabed of rippled sand.

David said, "From now on it gets simpler. There are only a few seaweeds-and at last, a billion years deep, only single-celled life, all the way back to the beginning."

"How much further?"

He said gently. "Bobby, we've barely begun. We must travel three times as deep as to this point."

The descent resumed.

The ancestor was a crude worm whose form shifted and flickered-and now, suddenly, she shriveled to a mere speck of protoplasm, embedded in a mat of algae.

And when they fell a little further, there was only the algae,

Abruptly they were plunged into darkness.

"Shit," Bobby said. "What happened?"

"I don't know."

David let them fall deeper, one million years, two. Still the universal darkness persisted.

At last David broke the link with the ancestor of this period-a microbe or a simple seaweed-and brought the viewpoint out of the ocean, to hover a thousand kilometers above the belly of the Earth.

The ocean was white: covered in ice from pole to equator, great sheets of it scarred by folds and creases hundreds of kilometers long. Beyond the icy limb of the planet a crescent Moon was rising, that battered face unchanged from Bobby's time, its features already unimaginably ancient even at this deep epoch. But the cradled new Moon shone almost as brightly, in Earth's reflected light, as the crescent in direct sunlight.

Earth had become dazzling bright, perhaps brighter than Venus-if there had been eyes to see.

"Look at that," David breathed. Somewhere close to Earth's equator there was a circular ice structure, the walls much softened, a low eroded mound at its heart. "That's an impact crater. An old one. That ice covering has been there a long time."

They resumed their descent. The shifting details of the ice sheets-the cracks and crumpled ridges and lines of dunelike mounds of snow-were blurred to a pearly smoothness. But still the global freeze persisted.

Abruptly, after a fall of a further fifty million years, the ice cleared, like frost evaporating from a heated window. But, just as Bobby felt a surge of relief, the ice clamped down again, covering the planet from pole to pole.

There were three more breaks in the glaciation, before at last it cleared permanently.

The ice revealed a world that was Earthlike, and yet not. There were blue oceans and continents. But the continents were uniformly barren, dominated by harsh icetipped mountains or by rust-red deserts, and their shapes were utterly unfamiliar to Bobby.

He watched the slow waltz of the continents as they assembled themselves, under the blind prompting of tectonics, into a single giant landmass.

"There's the answer," David said grimly. "The supercontinent, alternately coalescing and breaking up, is the cause of the glaciation. When that big mother breaks up, it creates a lot more shoreline. That stimulates the production of a lot more life-which right now is restricted to microbes and algae, living in inland seas and shallow coastal waters-and the life draws down an excess of carbon dioxide from the atmosphere. The greenhouse effect collapses, and the sun is a little dimmer than in our times."

"And so, glaciation."

"Yes. On and off, for two hundred million years. There can have been virtually no photosynthesis down there for millions of years at a time. It's astonishing life survived at all."

The two of them descended once more into the belly of the ocean, and allowed the DNA trace to focus their attention on an undistinguished mat of green algae. Somewhere here was embedded the unremarkable cell which was the ancestor of all the humans who ever lived.

And above, a small shoal of creatures like simple jellyfish sailed through the cold blue water. Farther away, Bobby could make out more complex creatures: fronds, bulbs, quilted mats attached to the seafloor or freefloating.

Bobby said, "They don't look like seaweed to me."

"My God," David said, startled. "They look like ediacarans. Multicelled life-forms. But the ediacarans aren't scheduled to evolve for a couple of hundred million years. Something's wrong."

They resumed their descent. The hints of multicelled life were soon lost, as life shed what it had painfully learned.

A billion years deep and again darkness fell, like a hammer blow.

"More ice?" Bobby asked.

"I think I understand," David said grimly. "It was a pulse of evolution-an early event, something we haven't recognized from the fossils-an attempt by life to grow past the single-celled stage. But it's doomed to be wiped out by the snowball glaciation, and two hundred million years of progress will be lost... Damn, damn."

When the ice cleared, a further hundred million years deep, again mere were hints of more complex, multicelled life forms grazing among the algae mats: another false start, to be eliminated by the savage glaciation, and again the brothers were forced to watch as life was crushed back to its most primitive forms.

As they fell through the long, featureless aeons, five more times the dead hand of global glaciation fell on the planet, killing the oceans, squeezing out of existence all but the most primitive life-forms in the most marginal environments. It was a savage feedback cycle initiated every time life gained a significant foothold in the shallow waters at the fringe of the continents.

David said, "It is the tragedy of Sisyphus. In the myth, Sisyphus had to roll the rock to the top of the mountain, only to watch it roll back again and again. Thus, life struggles to achieve complexity and significance, and is again and again crushed down to its most primitive level. It is a series of icy Wormwoods, over and over. Maybe those nihilist philosophers are right; maybe this is all we can expect of the universe, a relentless crushing of life and spirit, because the equilibrium state of the cosmos is death..."

Bobby said grimly, "Tsiolkovski once called Earth the cradle of mankind. And so it is, in fact the cradle of life. But."

"But," said David, "it's one hell of a cradle which crushes its occupants. At least this couldn't happen now. Not quite this way, anyhow. Life has developed complex feedback cycles, controlling the flow of mass and energy through Earth's systems. We always thought the living Earth was a thing of beauty. It isn't. Life has had to learn to defend itself against the planet's random geological savagery."

At last they reached a time deeper than any of the hammer-blow glaciations.

This young Earth had little in common with the world it would become. The air was visibly thick-unbreathable, crushing. There were no hills or shores, cliffs or forests. Much of the planet appeared to be covered by a shallow ocean, unbroken by continents. The seabed was a thin crust, cracked and broken by rivers of lava that scalded the seas. Frequently, thick gases clouded the planet for years at a time-until volcanoes thrust above die surface and sucked the gases back into the interior.

When it could be seen through the thick rolling smog, the sun was a fierce, blazing ball. The Moon was huge, the size of a dinner plate, though many of its familiar features were already etched into place.

But both Moon and sun seemed to race across the sky. This young Earth spun rapidly on its axis, frequently plunging its surface and its fragile cargo of life into night, and towering tides swept around the bruised planet.

The ancestors, in this hostile place, were unambitious: generation after generation of unremarkable cells living in huge communities close to the surface of shallow seas. Each community began as a spongelike mass of matter, which would shrivel back layer on layer until a single patch of green remained, floating on the surface, drifting across the ocean to merge with some older community.

The sky was busy, alive with the flashes of giant meteors returning to deep space. Frequently-terribly frequently-walls of water, kilometers high, would race around the globe and converge on a burning impact scar, from which a great shining body, an asteroid or comet, would leap into space, briefly illuminating the bruised sky before dwindling into the dark.

And the savagery and frequency of these backward impacts seemed to increase.

Now, abruptly, the green life of the algal mats began to migrate across the surface of the young, turbulent oceans, dragging the ancestor chain-and Bobby's viewpoint-with it. The algal colonies merged, shrank again, merged, as if shriveling back toward a common core.

At last they found themselves in an isolated pond, cupped in the basin of a wide, deep impact crater, as if on a flooded Moon: Bobby saw jagged run mountains, a stubby central peak. The pond was a livid, virulent green, and, somewhere within, the ancestor chains continued their blind toil back toward inanimacy.

But now, suddenly, the green stain shriveled, reducing to isolated specks, and the surface of the crater lake was covered by a new kind of scum, a thick brownish mat.

"...Oh," David breathed, as if shocked. "We just lost chlorophyll. The ability to manufacture energy from sunlight. Do you see what's happened? This community of organisms was isolated from the rest by some impact or geological accident-the event that formed this crater, perhaps. It ran out of food here. The organisms were forced to mutate or die."

"And mutate they did," Bobby said. "If not."

"If not, then not us."

Now there was a burst of violence, a blur of motion, overwhelming and unresolved-perhaps this was the violent, isolating event David had hypothesized.

When it was over, Bobby found himself beneath the sea once more, gazing at a mat of thick brown scum that clung to a smoking vent, dimly lit by Earth's own internal glow.

"Then it has come to this," said David. "Our deepest ancestors were rock-eaters: thermophiles, or perhaps even hyperthermophiles. That is, they relished high temperature. They consumed the minerals injected into the water by the vents: iron, sulphur, hydrogen... Crude, inefficient, but robust. They did not require light or oxygen, or even organic material."

Now Bobby sank into darkness. He passed through tunnels and cracks, diminished, squeezed, in utter darkness broken only by occasional dull red flashes.

"David? Are you still there?"

"I'm here."

"What's happening to us?"

"We're passing beneath the seabed. We're migrating through the porous basalt rock there. All the life on the planet is coalescing, Bobby, shrinking back along the ocean ridges and seafloor basalt beds, merging to a single point."

"Where? Where are we migrating to?"

"To the deep rock. Bobby. A point a kilometer down. It will be the last retreat of life. All life on Earth has come from this cache, deep in the rock, this shelter."

"And what," Bobby asked with foreboding, "did life have to shelter from?"

"We are about to find out, I fear."

David lifted them up, and they hovered in the foul air of this lifeless Earth.

There was light here, but it was dim and orange, like twilight in a smoggy city. The sun must be above the horizon, but Bobby could not locate it precisely, or the giant Moon. The atmosphere was palpably thick and crushing. The ocean churned below, black, in some places boiling, and the fractured seabed was laced with fire.

The graveyard is truly empty now, Bobby thought. Save for that one small deep-buried cache-containing my most remote ancestors-these young rocks have given up all their layered dead.

And now a blanket of black cloud gathered, as if hurled across the sky by some impetuous god. An inverted rain began, rods of water that leapt from the dappled ocean surface to the swelling clouds.

A century wore by, and still the rain roared upward out of the ocean, its ferocity undiminished-indeed, so voluminous was the rain that soon ocean levels were dropping perceptibly. The clouds thickened further and the oceans dwindled, forming isolated brine pools in the lowest hollows of Earth's battered, cracked surface.

It took two thousand years. The rain did not stop until the oceans had returned to the clouds, and the land was dry.

And the land began to fragment further.

Soon bright glowing cracks in the exposed land were widening, brightening, lava pulsing and flowing. At last there were only isolated islands left, shards of rock which shriveled and melted, and a new ocean blanketed the Earth: an ocean of molten rock, hundreds of meters deep.

Now a new reversed rain began: a hideous storm of bright molten rock, leaping up from the land. The rock droplets joined the water clouds, so that the atmosphere became a hellish layer of glowing rock droplets and steam.

"Incredible," David shouted. The Earth is collecting an atmosphere of rock vapor, forty or fifty kilometers thick, exerting hundreds of times the pressure of our air. The heat energy contained in it is stupendous... The planet's cloud tops must be glowing. Earth is shining, a star of rock vapor."

But the rock rain was drawing heat away from the battered land and-rapidly, within a few months-the land had cooled to solidity. Beneath a glowing sky, liquid water was beginning to form again, new oceans coalescing out of the cooling clouds. But the oceans were formed boiling, their surfaces in contact with rock vapor. And between the oceans, mountains formed, unmelting from puddles of slag.

And now a wall of light swept past Bobby, dragging after it a front of boiling clouds and steam in a burst of unimaginable violence. Bobby screamed-

David slowed their descent into time.

Earth was restored once again.

The blue-black oceans were calm. The sky, empty of cloud, was a greenish dome. The battered Moon was disturbingly huge, the Man's face familiar to Bobby- save for a missing right eye... And mere was a second sun, a glowing ball that outshone the Moon, with a tail that stretched across the sky.

"A green sky," murmured David. "Strange. Methane, perhaps? But how..."

"What," Bobby said, "the hell is that?"

"0h, the comet? A real monster. The size of modern-day asteroids like Vesta or Pallas, perhaps five hundred kilometers across. A hundred thousand times the mass of the dinosaur killer."

"The size of the Wormwood."

"Yes. Remember that the Earth itself was formed from impacts, coalescing from a hail of planetesimals that orbited the young sun. The greatest impact of all was probably the collision with another young world that nearly cracked us open."

"The impact that formed the Moon."

"After that the surface became relatively stable-but still, the Earth was subject to immense impacts, tens or hundreds of them within a few hundred million years, a bombardment whose violence we can't begin to imagine. The impact rate tailed off as the remnant planetesimals were soaked up by the planets, and there was a halcyon period of relative quiescence, lasting a few hundred million years... and then, this. Earth was unlucky to meet such a giant so late in the bombardment. An impact hot enough to boil the oceans, even melt the mountains."

"But we survived," Bobby said grimly.

"Yes. In our deep, hot niche."

They fell down into the Earth once more, and Bobby was immersed in rock with his most distant ancestors, a scraping of thermophilic microbes.

He waited in darkness, as countless generations peeled back.

Then, in a blur, he saw light once more.

He was rising up some kind of shaft-like a well- toward a circle of green light, the sky of this alien, prebombardment Earth. The circle expanded until he was lifted into the light.

He had some trouble interpreting what he saw next.

He seemed to be inside a box of some glassy material. The ancestor must be here with him, one crude cell among millions subsisting in this container. The box was set on some form of stand, and from here, he could look out over-

"Oh, dear God," said David.

It was a city.

Bobby glimpsed an archipelago of small volcanic islands, rising from the blue sea. But the islands had been linked by wide, flat bridges. On the land, low walls marked out geometrical forms-they looked like fields- but this was not a human landscape; the shapes of these fields seemed to be variants of hexagons. There were even buildings, low and rectangular, like airplane hangars. He glimpsed movement between the buildings, some kind of traffic, too distant to resolve.

And now something was moving toward him.

It looked like a trilobite, perhaps. A low segmented body that glittered under the green sky. Sets of legs- six or eight?-that flickered with movement. Something like a head at the front.

A head with a mouth that held a tool of gleaming metal.

The head was raised toward him. He tried to make out the eyes of this impossible creature. He felt as if he could reach out and touch that chitinous face, and - and the world imploded into darkness.

They were two old men who had spent too long in virtual reality, and the Search Engine had thrown them out Bobby, lying there stunned, thought it was probably a blessing.

He stood, stretched, rubbed his eyes.

He blundered through the Wormworks, its solidity and grime seeming unreal after the four-billion-year spectacle he had endured. He found a coffee drone, ordered two cups, gulped down a hot mouthful. Then, feeling somewhat restored to humanity, he returned to his brother. He held out the coffee until David-mouth open, eyes glazed-sat up to take it.

"The Sisyphans," David murmured, his voice dry.

"What?"

"That's what we must call them. They evolved on early Earth, in the interval of stability between the early and late bombardments. They were different from us... That methane sky. What could they have meant? Perhaps even their biochemistry was novel, based on sulphur compounds, or with ammonia as a solvent, or..." He grabbed Bobby's arm. "And of course you understand that they need have had little in common with the creatures they selected for the cache. The cache of our ancestors- No more than we have with the exotic flora and fauna which still cling to the deep-sea vents in our world. But they-the thermophiles, our ancestors-were the best hope for survival..."

"David, slow down. What are you talking about?"

David looked at him, baffled. "Don't you understand yet? They were intelligent. The Sisyphans. But they were doomed. They saw it coming, you see."

"The great comet."

"Yes. Just as we can see our own Wormwood. And they knew what it would do to their world: boil the oceans, even melt the rock for hundreds of meters down. You saw them. Their technology was primitive. They were a young species. They had no way to escape the planet, or outlive the impact themselves, or deflect the impactor. They were doomed, without recourse. And yet they did not succumb to despair."

"They buried the cache-deep enough so the heat pulse couldn't reach it."

"Yes. You see? They labored to preserve life-us, Bobby-even in the midst of the greatest catastrophe the planet has suffered.

"And that is our destiny, Bobby. Just as the Sisyphans preserved their handful of thermophilic microbes to outlive the impact-just as those algal mats and seaweed struggled to outlast the savage glaciation episodes, just as complex life, evolving and adapting, survived the later catastrophes of volcanism and impact and geological accident-so must we. Even the Joined, the new evolution of mind, are part of a single thread which reaches back to the dawn of life itself."

Bobby smiled. "Remember what Hiram used to say? "There's no limit to what we can achieve, if we work together."

"Yes. That's it exactly. Hiram was no fool."

Fondly, Bobby touched his brother's shoulder. "I think."

- and, once again, without warning, the world imploded into darkness.