Prolog 70 million years ago Five thousand meters down, at the bottom of a cold, dark ocean, a fissure has cracked the seabed. Subterannean water, superheated by the magma core, spews forth, bringing from below sulfurs and other chemicals in a dense black cloud. Clustered around the little mound that edges the fissure are long, pale tendrils, looking like giant worms, swaying in the current. Other, smaller organisms without form drift in and out of the tubeworm forest, riding the random currents from the churning "black smoker" vent. Amazingly, these creatures have developed and flourished in this total absence of light. The hydrothermal vent provides warmth, and the chemicals and minerals it spews provide them nutrients. This is the only way it can be, this deep in the ocean, where no clorophyll-based life can exist. Sunlight could never penetrate so much water, even if a two-kilometer-thick crust of ice didn't envelope the surface. Over time, the amoeba creatures learn to forage for particles in the water and on the seabed. They become independent of the smoker vents which they now occasionally encounter in their deep-sea travels. Some amoebas have long, cilia-covered tentacles, which they strain particles from the water with as they travel. However, most of the creatures in this ocean have retained their basic, gelatinous form. Then the comets come. Hurled from the Oort cloud by the passing of a far- orbiting star which would someday be named Nemesis, hundred of comets are tossed into the solar system. Some of the young planets they encounter are devestated. Neptune intercepts several in a row and is knocked on its side. Like a turtle on its back, it is doomed to forever spin 90 degrees off-axis. Saturn sucks two passing comets into its gravity and tears them apart, adding sparkling rings of ice particles to its collection of rocky debris rings. Earth suffers perhaps the worst. Of all the planets, it has enjoyed a grand success of thriving life. Lush jungles and gigantic reptilian forms inhabit nearly every available land mass. The seas teem with hundreds of thousands of species. A new life form, covered with fur and not scales, capable of life birth and suckling its young, has recently emerged. It has overcome its initial evolutionary weaknesses and appears as though it may actually survive to develop into species larger than rodents. All of that ends in a matter of seconds. The first comet strikes high in the northern hemisphere, in the midwestern sea. Nothing within a thousand kilometers survives the shock wave, earthquakes and tital waves that accompany the impact. Black clouds of dust cloak the Earth and dim the sun. Vaporized water soon becomes dust-blackened clouds, and muddy rain falls across the planet. Once-clean watering holes become brown and undrinkable. Plants wither in the feeble light. Under normal circumstances, these things would taper off and clear up in a couple of years, and life would restore itself. But the next spring another comet hits, repeating and adding to the devestation. Around the planet, life falters. Then, toward the end of fall, the third and largest comet impacts at a low angle near the equator. The force is so great that Earth's spin actually slows, and the days become slightly longer. There is virtually no hope for what little life remains. Perhaps the new rodent-sized creatures, with their omnivorous diet and insulating fur, will find a way to eeke out an existence. Perhaps someday in the far future we will be able to look upon this planet again and find out. The destructive path of the comets has touched even the largest body in the solar system. Several comets punch into Jupiter's thick atmosphere and vaporize in seconds, leaving only dark, sooty blotches. The violent moon Io receives a blow, but is barely affected; its volcano-dotted surface will cover the scar soon enough. Europa is a different matter. A rocky comet strikes the western hemisphere obliquely. It shatters the two-kilometer ice sheath like an eggshell and exits like a bullet in the eastern hemisphere in a geyser of water that instantly flash-freezes into huge chunks. In fact, this is mostly the result of a combination of stress-faults rupturing on the surface and submarine shock waves; the majority of the comet itself pulverized and fused with the surface ice. The chunks of ice blown out of Europa are drawn by gravity toward Jupiter. Slowly, they fall into the upper atmosphere, melting from the size of a small city to the size of city blocks as they tumble. Further down, they have become the size of houses, then cars, then are gone altogether. But water is not the only thing that has been ejected from the Europa. Thousands of the amoebas were caught and flash-frozen. Now a slow rain of the dead, collapsed creatures falls toward Jupiter's liquid-metal surface. Long before then, they will have been crushed into near- nothingness by the intense atmospheric pressure. Jupiter will never notice their existence. But not all of the amoebas are dead. Several hundred emerged from the ice still alive. Many of these survive for only a few seconds, but others find the hydrogen- and sulfur-rich atmoshere to their liking. The pressure is similar to where they lived on Europa, and they can ride the winds much the same way they rode Europa's currents. Their bodies inflated with air, they become spherical, and over time their outer membranes evolve a clorophyl cell structure to take advantage of the new sunlight. The amoeba creatures spawn new species, some with tentacles for a swim-style manouverability, some with flattened wing-like appendages that allow them to glide and dive like birds. And the evolutionary wheel spins...