"I've also determined the origin of the rats."
"They're under control. We're doing nicely."
* * * * *
On the contrary, thought Marin. He searched for the proper beginning.
"Glade has an Earth-type climate and topography," he said. "Has had
for the past twenty thousand years. Before that, about a hundred
million years ago, it was also like Earth of the comparable period."
He watched the look of polite interest settle on the executive's face
as he stated the obvious. Well, it _was_ obvious, up to a point. The
conclusions weren't, though.
"Between a hundred million years and twenty thousand years ago,
something happened to Glade," Marin went on. "I don't know the cause;
it belongs to cosmic history and we may never find out. Anyway,
whatever the cause--fluctuations in the sun, unstable equilibrium of
forces within the planet, or perhaps an encounter with an interstellar
dust cloud of variable density--the climate on Glade changed.
"It changed with inconceivable violence and it kept on changing. A
hundred million years ago, plus or minus, there was carboniferous
forest on Glade. Giant reptiles resembling dinosaurs and tiny mammals
roamed through it. The first great change wiped out the dinosaurs, as
it did on Earth. It didn't wipe out the still more primitive ancestor
of the omnivore, because it could adapt to changing conditions.
"Let me give you an idea how the conditions changed. For a few years a
given area would be a desert; after that it would turn into a jungle.
Still later a glacier would begin to form. And then the cycle would be
repeated, with wild variations. All this might happen--did
happen--within a span covered by the lifetime of a single omnivore.
This occurred many times. For roughly a hundred million years, it was
the norm of existence on Glade. This condition was hardly conducive to
the preservation of fossils."
Hafner saw the significance and was concerned. "You mean these
climatic fluctuations suddenly stopped, twenty thousand years ago? Are
they likely to begin again?"
"I don't know," confessed the biologist. "We can probably determine it
if we're interested."