It's been suggested that once a civilisation learns to recycle its raw materials it would disappear from the archaeological record. Modern humans have been around for at least 40 thousand years, and probably 90, whereas our particular civilisation only stretches back to the end of the last ice age.chrismb wrote:I have gone on to make the following 'challenging' speculation, just to crank the amusing debate; not all coal was formed by decomposition of trees, etc., it is also the remains of buried charcoal from attempted carbon capture from previous failed civilisations billions of years ago!
That leaves plenty of room for speculation. You see, the glaciers destroyed the evidence...