The Earth presented in this game is Earth Mark II
From what we know in The Hitchhiker's Guide to the Galaxy, Earth was demolished, but a new one was rebuilt in a factory, and it took manual labor to reconstruct every bit of its natural parts, not to mention that the life cycle itself was started manually to finish off the final touches. So, what if, being manmade, the interior of the planet was mechanical as well because of that? After all, there were humans from the present day overseeing the World Works system, as both Osgoods' logs show, while there were dinosaurs still around.
