Of course I agree that a lot of time had to pass in order for all of the changes to occur ... but if Blue is not Urth, then the double limbed inhabitants of Blue could have been evolving or engineered when the first colonizers approached the planet - and the ruins of the vanished people on Green could indeed be the ruins of the vanished people of Urth - not double limbed people, just dead people. I think that not as much time would HAVE to pass if we allow that animals can change so completely in one generation, if we unquestionably accept an offhand statement by a character to be a steadfast hold on the timeline. I am not prepared to believe that the quote Roy provided is a definitive limit to the time that passed - but it could be a reasonable approximation of a very long time. Just trying to work with information as it is presented. Marc Aramini