"It appears that consciousness is a very rare & precious thing & we should take whatever steps we can to preserve the light of consciousness. Only now, after 4.5 billion years has that window been open. That’s a long time to wait and it might not stay open for long.” -
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His follow up comment was more interesting in that it took 4.5 billion years for humans to exist but (in something like) less than a few hundred million years, the earth will not be able to sustain human life.