Could an industrial civilization have predated humans on Earth?
If there were an industrial civilization here before us (modern humans) then it would be astonishing that in all of the fossils we have discovered, we've never yet discovered a single ancient nut, bolt, screwdriver, wrench, etc.  Not one single wire or cast metal part.<p>As per the article, that civilization would have to predate all of the vast history of evolution that we know of.  Wouldn't some higher life forms from such an earlier civilization have been in the fossil record?