Well, the carbon our civilization has been burning started forming about 350-300 million years ago (from Carboniferous period, it's in the name), and the Siluri

Well, the carbon our civilization has been burning started forming about 350-300 million years ago (from Carboniferous period, it's in the name), and the Silurian period was 420-440 million years ago, so what Silurians would have had under their tentacles isn't what we bootstrapped our society with. Maybe they used plenty of the under-your-tentacles fuel sources, but it's been a very long time since, and it's hard to tell. https://en.wikipedia.org/wiki/Geologic_time_scale https://en.wikipedia.org/wiki/Geologic_time_scale