Is the fundament supposed to be Saturn? It has the same number of (named) moons… and is a gas giant. Apparently a shard of the Hive home world broke off, and collided with a gas giant, floating in its atmosphere. The events in the Book of Sorrow began a LONG time ago… and Oryx mentions possibly wanting to return to the Fundament at some point to see how things have gone.

So did all this happen before any life evolved on Earth? Or is it just some random gas giant elsewhere?

Elsewhere. Since Fundament soon had less moons:

In the beginning we rode hollow moons from star to star.

That and Saturn has 53 named moons while Fundament had "52 and One." With the One being The Traveler which also left.

So did all this happen before any life evolved on Earth? Or is it just some random gas giant elsewhere?