7 new Earth-like exoplanets discovered, NASA announces

Yes, Pellucidar was lit and warmed by a sun-like object in the exact center of the Earth. This sun either puts out less UV than ours or the Pellucidarian atmosphere is better at blocking it, because characters of Caucasian background tan but don't burn. The "sun" takes of a degree and a half of of the sky (wow, the sun's three times as big as back home!) and neither moves nor ever dims, therefore it is always noon and the inhabitants have to concept of time.
As for your idea of a wildlife park for extinct animals and a civilization which fell, I think that could work. Since I've already got to use time travel to get my egar young man and aging professor together (they meet at Woodstock), I'll use that for how the animals got there, but I might still need the culture which put them there to fall.
Thanks for giving it some thought, Mike!