I enjoyed this comment on the subject from a few years ago, focusing on a search for carbon cenospheres as a sentinel for an earlier civilization: https://news.

I enjoyed this comment on the subject from a few years ago, focusing on a search for carbon cenospheres as a sentinel for an earlier civilization: https://news.ycombinator.com/item?id=16837470 https://news.ycombinator.com/item?id=16837470