I'm beginning a science fiction novel that begins a billion, or possibly several billions, of years in the future. Given the best quality structures humans can make out of the longest lasting materials we have, what would buildings and other structures look like after that long of a period of time? And that is exposed to wind, rain, snow, and even the intense heat of the sun far into the future. What about underground structures that aren't exposed to the elements? Do they still show signs of degradation after billions of years? Would they even exist as structures after that long? Even if they're metal or glass? What about an object made of various materials kept in a vacuum? Would it still show signs of degradation after such a long time as billions of years? I know what happens to things in certain conditions after hundreds or even thousands of years, but after billions, that's a whole other story. Thanks.