THIS has been keeping me awake at nights so it might as well worry you as well.
I have been reading a book by one Graham Hancock called Fingerprints Of The Gods. The title and the design of the cover are clearly intended to appeal to fans of that genre pioneered by Erik von Daniken in which ancient artifacts and ruins are scrutinised for evidence of visiting spacemen.
That would normally be enough to put me off. But Hancock is not a fruitcake. His last recorded job was as a foreign correspondent for The Economist, a publication not noted for mysticism. The book was well reviewed by respectable newspapers.
Hancock's thesis is that in the thousands of years before recorded history in our modern sense started, there was plenty of room for an advanced and technically adept civilisation.
It only takes three or four thousand years, after all, to go from near scratch to manned flight.
Why is this advanced civilisation no longer with us? Well, there have been plenty of ecological catastrophes over the years, too. Something rather less than the upheaval that wiped out the dinosaurs would produce a very serious setback for an urban civilisation. And there are traces.