On a world with gravity similar to Earth, I understand that you start running into intolerable heat around two or three kilometers down. Of course on the planet Lakshmi, people have the technology for great fans to circulate the air, and I understand that D'ni-type underground watersheds do, in fact, cool things down a bit. This is a community cut off from the surface when nuclear war broke out between the peoples of Lakshmi's two supercontinents and a blast sealed the only entrance. There is air recycling (it helps that there are D'ni-type lakes here and there) and many caverns are dedicated to hydroponics farming. Assuming gravity comparable to Earth's and a now-lost entrance less than fifty meters above sea level, how far down could one live with good air circulation?
"You don't fix faith. It fixes you." -- Shepherd Book, Jaynestown[br][br]Never meddle in the affairs of Daleks, for you are mortal and look good in photo-negative.
What's so interesting to me is that even though they were several miles down, they still hit water. Remains of the "fountains of the deep" that were broken up to make Noah's Flood?
Geology of your planet may vary, of course. If you wanted them to live more than two miles down, you could just cool the core of your planet so more of the crust/mantle was inhabitable. This would have bad implications for the surface, but underground it'd be nice.
Also, the D'ni got resources and food for their civilization through their Books and the worlds on the other side. I think without that, they'd have died off much quicker. I think that's why the Linking Books were so important.
<-- closet Myst nerd
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