Though the planet Earth had taken an enormous amount of damage from
the impact of the Dinosaur Killer, the effects were in truth less
severe than they appeared.  The mass extinction brought about by the
D-K was only a shadow of the effects of the earlier Permian
Extinction.  Where the previous assault had extinguished over 95% of
all animal species, the K-T extinction had seen the end of fewer than
50%, with even smaller percentages of plant species gone.

The recovery from the K-T Extinction was faster than it had been from
the Permian event.  Seeds lay dormant under sheets of ash, waiting for
better conditions to germinate and grow.  Many small species had had
endured the heat, the cold, the rains, and the darkness, and now they
had inherited a nearly empty world into which they could expand and
differentiate.

Just as the previous attack of NEMESIS had marked the of the
Paleozoic, the era of 'ancient life', this new attack marked the
beginning of end of the Mesozoic, the age of 'middle life'.  A new
geological era began with the new Tertiary Period.  Now Pangaea was no
more than an Eldren memory, as the separate continents began to drift
toward positions somewhat recognizable to a modern human. The Atlantic
Ocean had opened up in the Cretaceous, in the Tertiary it widened and
deepened.

The tiny insectivores, predators, and fruit eaters of Class Mammalia,
so long scurrying in the shadow of the dinosaurs, now spread across
the empty lands like wildfire, generating new species at a tremendous
rate.  Some remained in or took to the trees, others spread onto the
plains, settled into the newly regrown forests, or began to hesitantly
return to the sea.

Though the promising pseudo-birds were now extinct, and many of the
most promising bird species with them, NEMESIS did not succeed in
exterminating the Aves Class.  It had not really expected to
accomplish that, but it had hoped for it.  Unfortunately, from the POV
of the NEMESIS entity, the birds proved to be a durable breed, and
over the course of the Tertiary Period they recovered from their
losses at the K-T Event and then continued to differentiate into
countless niches.  None, though, ever showed the hint of presapience
that their ancestors had displayed in the late Cretaceous, and which
had earned them a death sentence from NEMESIS.

The D-K had succeeded (with help) in wiping the great oceanic
reptilian predators such as the mososaurs from the seas, but their
cousins the snakes survived, returned to the land, and thrived.

The warm, mild global conditions had that characterized much of the
Cretaceous did not immediately end with the K-T transition, but a
gradual deterioration of climatic conditions did occur.  The climate
warmed again during the early Eocene Epoch, about 57-34 million years
ago, with subtropical forest reaching to the general neighborhood of
the Arctic Circle, but the warmth did not hold throughout the epoch.
Many of the familiar Mammalian orders emerged during this time.  The
first primates, bats, hoofed mammals, and the early cetaceans put in
their initial appearance during this time.

Three broad types of mammals, the placentals, marsupials, and
monotremes, struggled for primacy, with the placentals winning a
decisive victory, the marsupials taking the silver, and the
monotremes, the odd egg-laying mammals, reduced to a handful of
species.

As the Eocene closed out, the temperature decline continued, driven in
part by further continental splits between Australia and Antarctica.
As Antarctica was propelled south, the formerly verdant land began to
build up the first thin layers of what would in time become the
miles-thick Southern Ice Cap.  In the northern hemisphere, the
subtropical forest was driven south, as cool temperatures returned to
the high latitudes.

The Oligocene Epoch saw the emergence in North America of the first
camels, of true (though still small) bears, the following warmer
Miocene the first true horses, again in North America.  This later
period saw the emergence of the true grasses, which transformed the
ecosystem of the planet.  Animals adapted to thrive on the tough,
silica-rich grasses could tap into an immense potential source of
food, but the adaptations could also leave some species so specialized
as to be able to live on few things other than various grasses.

The mild middle Miocene was the last period of global warmth, like a
final drawing-of-breath.  The onset of the Pliocene, 5 megayears
before the present, brought a sharp acceleration of the global cooling
trends.  Ice cover appeared on the open Arctic Ocean, and tundra
replaced forest in the northern reaches of Asia, North America, and
Europe.  Antarctica was fully ice-bound, the sea levels were lower,
and the world colder and drier than it had been even a few million
years before, and the trend was accelerating.

Finally, the Pliocene gave way to the Pleistocene, and the Ice Ages
began.  Great ice sheets spread out across North America, Europe, and
Asia, advancing southwards and lowering global sea level enormously,
only to temporarily retreat during the brief, warmer 'interglacial'
periods.  This cycle repeated over and over, wiping out many species
and encouraging adaptation in others.  The southern hemisphere was
spared the worst of the ice sheets, since the ice mass in Antarctica
was fenced off from South American and Africa by the ocean, but the
cold and dry conditions did not spare the southern lands.

In the Atlantic Ocean, still slowly, steadily widening under the
impetus of the outflowing new oceanic crust from the Mid-Atlantic
Rift, a modest magma plume had reached the surface, along the general
region of the Rift.  In no mood to take chances, after the relatively
recent disaster of the Dinosaur Killer impact, the Watcher decided to
modify the geology of the region to reduce the risk of a global-effect
eruption series.

Instead, a geologically peculiar island complex rose in the middle of
the Atlantic, an odd but distinctly temporary feature, a sort of
artificial version of the smaller island of Iceland to the north.  In
later times, this odd, self-contained island mini-continent would be
known as Atlantis.[1]

Now the lands and seas would have appeared very familiar to a modern
observer.  The flora and the fauna were of types and shapes and sizes
familiar to the gaze of a modern human.  The Earth had recovered from
the Dinosaur Killer long since, but that crucial event was far from
forgotten.

The Eldren had been caught off-guard, again. It did little to improve
their mood that the damage was far less in in the K-T Event than it
had been previously.  Yet again, a fascinating and unimaginably
complex ecosystem had been irretrievably destroyed, and if the new one
rising in its place was also fascinating, it did not change the fact
that the previous one had been a painful loss.

The Watcher, for its part, was fed up.  Determined to make sure their
mysterious enemy could not repeat the D-K attack, the Familiar Eldren
proceeded to spend over a quarter million years sweeping most of the
larger NEO rubble piles into the outer Solar System.  Only a handful
of rocks remained that crossed the orbit of Earth, most of them small
and unlikely to impact.

Of course, new rocks were periodically perturbed onto Earth-crossing
orbits, but usually the Eldren swept them out again.  On a couple of
occasions, big rocks _did_ get through, but the Eldren knew how to
cope with that now, and in each case they were able to localize the
damage and prevent a major mass extinction.  NEMESIS noted this last
through its hidden eyes with disturbed interest.

The ease with which the Eldren contained and repaired the damage from
what should have been global-disaster level impacts made it clear to
the ancient living computer that another Dinosaur Killer type attack,
even if it could have readily arranged such, was by no means
guaranteed to be effective.  Concluding from this (and other examples
of increased Eldren preparedness elsewhere in the Greater Milky Way)
that piecemeal attacks should be avoided where possible, NEMESIS
focused still more of its attention on its steadily maturing plans for
its next full-scale attack on Solarigen life, its next attempt at
total extirpation of the problem.

As well as it could, it kept a close 'eye' on the Solarigen worlds,
but it didn't have the clear view in had possessed in the Paleocene,
and there were more worlds than ever now.  By the beginning of the
Pleistocene, the Eldren had raised the number of living Solarigen
worlds in the Greater Milky Way over well over 100 million.  It should
be noted that they had never entirely ceased spreading helium-based
life, as well.  Along with the 100 million Solarigen worlds, the
Eldren still watched over and observed 10 million or so Heliugen
biospheres.  NEMESIS had no brief for the Heliugen worlds, however.

As for the Helialisks, they continued to watch for the actions of
NEMESIS, hoping to blunt or stop those actions before they could serve
to infuriate the Eldren and perhaps lead the disclosure of the
existence of the Helialisks.  But their efforts were less strong at
the end of the Cretaceous than they had been at the end of the
Permian.

Roughly 200 million years separated the first and second of NEMESIS'
great assaults on Earth.  The time between them was almost as great as
the time from the creation of the Helialisks to the Permian
Extinction.  There were far fewer Helialisks left 'operational' at the
end of the Cretaceous than there had been at the end of the Permian.

The reasons were varied.  Sometimes, in spite of the best efforts, a
natural disaster would damage or destroy a Helian Graveyard.
Improbable events can turn out to be nearly inevitable in hundreds of
millions of years.  But the Last Helians had planned well, and most of
the Graveyards were in very, very, calm safe places.

A more common failing of their big for immortality was that the Last
Helians, being mortals themselves, had had _no conception_ of how long
even a million years could be.  As the millions mounted up into the
tens of millions, and then the hundreds of millions, many of the
Helialisks who had hoped to outlive the stars found themselves losing
interest in the project.

This 'saturation' befell some far sooner than others, of course.  The
first 100 million years of the history of the Helialisks it was a rare
thing, so strong was the native desire of the Last Helian psyche to
endure and so well had they prepared.  But after 100 million years
this condition began to appear more and more often.  By the end of the
Cretaceous, only about 30% of the original Helialisks were still
meaningfully functional.

The results of a loss of interest in continuation could very in
detail.  A few of them simply shut themselves down, a form of suicide.
 But most simply gradually slipped from the slow, steady, glacial
thought pattern that was the norm for the Helialisks into a
repetitive, ever less varied pattern, almost a trance state, and when
they finally slipped into that trance fully, they never emerged.  The
life-support systems of the given monolith still operated, the Helian
organs-of-thought preserved inside continued to live in a biological
sense, but all reaction to stimuli and all interaction ceased.

A Helialisk in that state could continue on for a very long time
before the organs-of-thought finally died from lack of mental
activity, millions of years at times.  But for all practical purposes
a Helialisk in that full trance state was already dead.[2]

Thus the resources of the Helian Graveyards steadily declined over the
course of the Mesozoic.  By now, none of the surviving Helialisks, not
even the surviving original conspirators, had the slightest interest
in their former helium-biosphere homeworlds, and the entire 1.5
million year history of the Helian galactic civilization was a trivial
footnote in their multi-megayear memories.

Thus NEMESIS continued to dutifully execute programming based on
priorities of relevance to nobody, and opposed by the some of the very
beings who had once held those goals.  It was an irony worthy of a
laugh, save that no Helialisk had a sense of humor nor any ability to
comprehend 'irony'.

No more than the Helialisks did NEMESIS have either a sense of humor
or a sense of irony.  The ancient machine had its programmed
priorities and it was executing its programming, that was enough for
it.

So now, let us step back to the dawn of the Pliocene, ~5 million years
ago.  Earth was recognizably modern in form.  The outline of the
earlier history was told, the stage was set, most of the players were
ready to begin the show.

The Eldren, the Helialisks, NEMESIS, and other players yet to be
introduced were already in the great game, but now a new actor, as yet
unsuspected by any of the others, was about to step onto the stage,
and the story was about to become very strange.

MORE LATER.

                                                  Shermanlee

[1]We're finally starting to come back to where we started from (but
we're not there yet).  :)