Yep, one more coming to cap this series. By the way, one more thing for your list of what will be different from the previous cave era, or at least a big reason why civilization will not rise as quickly next time, is that there will be no easy-to-get-at fossil fuels, so no industrial revolution. Just water wheels and heat from the sun. And only guano for fertilizer. The incredible 1949 book, "Earth Abides," recommended by Richard Crim in response to my column Essential Climate Change Fiction, illustrates how all modern knowledge will disappear in just a few generations.