So why hadn’t this already happened? Why was there no sign of traffic among the stars? Why had the predicted galactic radio network of communications never been detected?

Even more puzzling… why was there absolutely no evidence that Earth had ever been colonized in the past? We were by then quite certain that our world had never hosted visitors from other worlds.

For one thing, there was the history of the Precambrian to consider.

Before the age of reptiles, before fish or trilobites or even amoebae, there was, on Earth, a two-billion-year epoch in which the only lifeforms were crude single-celled organisms without nuclei—the prokaryotes—struggling slowly to invent the basic structure of life.

No alien colonists ever came to Earth during all that time. We knew that for certain, for if they had, the very garbage they buried would have changed the history of life on our planet. A single leaky latrine would have filled the oceans with superior lifeforms that would have overwhelmed our crude little ancestors.

Two billion years without being colonized… and then the silent emptiness of the radioways… the philosophers of the twenty-first century called it the Great Silence. They hoped the starships would find the answer.

Then the very first ship, Seeker, somehow smashed the crystal-sphere we hadn’t even known existed, and inadvertently explained the mystery for us.

During the ensuing CometWar, we had little time for philosophical musings. I was born into that battle, and spent my first hundred years in harsh screaming littleships, blasting and herding iceballs that, left alone, would have fallen upon and crushed our fragile worlds.

We might have let Earth fall then. After all, more than half of humanity at that time lived in space colonies, which could be protected more easily than any sittingduck planet.