Earth isn’t gone. But sometimes, we wish it was.
When all this started, we’d just achieved long-range spaceflight with the Cleave drives – my great-grandparents were on one of the first cruisers out to the Alpha Centauri system. Kind of a big deal, getting to escape the solar system like that. We’d managed to colonize a few worlds in our backyard, but ideal they weren’t; if we could get our ships to cut through interstellar space the way they did in our neighbourhood, we might have a better chance at finding a liveable world.
Terraforming? That’s a fool’s errand. Best you can hope for is to change a series of icy moons into windy dustballs that snow like the devil’s dandruff, or make a bunch of dry rocks into slightly moist ones. ‘Course, other folks in the galaxy might have other notions, but they weren’t around then; it was just humans trying to find a new home in the badlands.