From the guys who bought you Who Built The Moon?: and if you've read that (I have), then in many ways the title for this forms a bit of a run-on sentence that takes away a little bit of the suspense here. But then this isn't posited as a question. (You know the guys...) Who Built The Moon? Well, They Built The Earth. In reality, this is almost just another edition of Who Built The Moon, with updated science to goof off on since the first book came out. It also interpolates another of their books, Civilization One (which I haven't read), to build some wonderful conspiracy theory that alternately people in power are hiding from us, or haven't realised yet.

They Built The Earth doubles down on the mathematical coincidences of Who Built The Moon to suggest that the moon was artificially constructed, and (in this case) the Earth was also bombarded by a destroyed planet to create the conditions for DNA to happen. It's an odd way around their core thesis, which is a Panspermia hypothesis, namely that life of Earth was seeded here. This is not an uncommon theory, and Butler and Knight, as ever, enjoy cherry-picking the scientists who in later life, got on the Panspermia Express (whilst grabbing sentences for Sagan and Hawking that buoy up their side). The amount of time, however, they spend discussing the nonsense film Moonfall, just because its (very different) theory of an artificial moon was broadly based on someone half seeing the title of their previous book in a bookshop, does go to show the straws they are often clutching. They are fond of reminding us how astronomically unlikely the spontaneous development of life on Earth is, and then invoke this to show that it must be artificially induced only to then come up with a theory that requires the invention of something that is seemingly theoretically impossible, philosophically paradoxical and still it seems hugely improbably to nail that the solution. We Built The Moon, was the thesis of Who Built The Moon, humanity or its descendants traveled back in time to set up the conditions required. But we also built the Earth at a different timescale, crudely terraforming it. And have we intervened in the meantime - it seems not, though I daresay "They Lit The Sun" may be on its way in another twenty years. Know your enemy: they are always a fun, if unconvincing, read.