Donald Moffitt - Genesis 02

But it’s only twelve million years later.”
    “Close enough,” Jao said. “Now, let’s skip back one hundred and fifty-five million years to the other really major crisis. The one that wiped out half of all animal families on Earth. Have we got a secondary extinction associated with it?”
    “Yes,” Ame said, catching her breath. “A bigger one this time. A very large extinction of marine organisms that could fall within a ten-to fifteen-million-year period. We couldn’t fit it into our data before without stretching it.”
    “All in knowing how,” Jao said with a grin, while Smeth smoldered.
    Jao thickened the axis and shaded it over to include the following arm. “Very interesting,” he said. “The two big ones are at right angles to each other. Forming two arms of the older cross. And it’s the arms sprouting in their wake that turn out to be the real killers.”
    “As if whatever it is was getting stronger,” Ame suggested.
    “Yah.”
    “Jao—”
    “Not yet. Let’s fill in as many blanks as we can first.”
    Over the next several minutes they assigned eleven extinction episodes to the rotating spokes. Nine of them fit the pattern of the eight major spokes, and two fell within the secondary following position.
    “How do you explain the missing pieces?” Smeth asked.
    “How should I know?” Jao rumbled. “Insufficient data. Fluctuations in the strength of the spokes. Maybe factors that we haven’t figured yet. The sun catches up with a spiral arm every hundred million years or so and stays inside for ten million years. It bobs up and down through the plane in a thirty-three-million-year cycle, if it behaves like the other stars at that radius. Maybe the dust intensifies the killer effect on some passes. Maybe it does the opposite and acts as a shield. Why don’t you try to combine all the cycles and see what you can work out? The important thing is that everything we do have fits the pattern.”
    His belligerence died. Like everybody else in the observatory he was staring at the one big fact that hung before them in the rotating holo image.
    “The ninth extinction and the first extinction are doubled up on the same spoke,” Ame said in a half whisper.
    “It came back again for a second swipe,” Jao said.
    “The second visitation was the last extinction before human beings evolved.”
    “The first swipe was the big double event,” Jorv said. “First the trilobites and all that plankton—ninety percent of sea life. Then half of all animal life on Earth.”
    “And if there was a … a similar follow-up,” Ame said, “it would have come at just about the same time that Original Man disappeared from the universe.”
    Smeth’s harsh voice grated through the ensuing silence.
    “It couldn’t be. Man is an intelligent being, not a—a dinosaur! He would have found some way to protect himself. Or flee. After all, it isn’t as if the entire Milky Way was sterilized the way the Father World’s galaxy was. Some life survived each of these—extinctions and went on to evolve.”
    “When the dinosaurs disappeared,” Jorv said, his young voice getting away from him, “no species of land animal weighing more than twenty pounds survived. Man’s ancestors were very small and primitive. It was the highly evolved species that went. The second time around, that was man.”
    Jao stared thoughtfully at the rotating orange arms of his holo model. “Original Man had only spread a few hundred light-years. At most, a few thousand. You can’t travel faster than the speed of light. You can’t outrun something that extends to the galactic rim and sweeps the galaxy laterally. They could only have caught up with the previous killer arm.”
    He retreated into gloomy contemplation. Nobody else seemed very lively, either. Bram was just about to say something, when Jun Davd did it for him.
    “Let’s not jump to conclusions,” Jun Davd said. “This is all highly speculative. Jao doesn’t have a theory, just a hypothesis. We need more data. We’ll set up a long-term computer model and keep feeding our observations into it.”
    “Yah, I’ll get on that today,” Jao said.
    Jan Davd went on, “Original Man’s sector of the galaxy is about thirty thousand light-years from the center, and on our outward spiral, we’ll sweep great areas of the disk over a real-time period of tens of millennia. We’ll be able to make observations that were not possible for Original Man, no matter how much