Why would Earth need terraforming? Well, what if a giant meteorite smacked into the planet, asks grandmaster Williamson (The Silicon Dagger, 1999, etc.), wiping out all life? Rich eccentric Calvin DeFort insists that a major meteorite impact is likely, and dedicates his life to creating Tycho Base on the Moon, run by a computer, staffed by robots, and complete with frozen human-, animal-, and plant-tissue specimens. When the fateful meteorite duly shows up, devastating Earth, only DeFort's chosen handful escape. Thousands of years later, the computer prepares clones of the original survivors. They study the records intensively until it seems as though they have the actual memories of their originals. Astronaut Pepe and biologist Tanya travel to Earth, finding conditions still hostile; in the interim, weird octopus-like amphibians have evolved. Both explorers perish, however. Many years pass. Tycho Base’s computer raises a new crop of clones who study both the ancient records and those more recent. Their attempt to repopulate the planet succeeds, after a fashion; survivors build a Moon-worshipping civilization whose citizens don't believe that their visitors are really from the Moon. Another impact wipes them out. Millions of years later, the latest clones awaken to discover alien invaders; still later, new clones are raised by humans so advanced that Tycho Base and its contents have been preserved as historical artifacts.
Sweeping, imaginative, and captivating: As good as, perhaps better than, anything Williamson has written in his long and astonishing career.