We think we`re the first advanced earthlings-but how do we really know?
(PHYSorg.com Space & Earth)

Imagine if, many millions of years ago, dinosaurs drove cars through cities of mile-high buildings. A preposterous idea, right? Over the course of tens of millions of years, however, all of the direct evidence of a civilization-its artifacts and remains-gets ground to dust. How do we really know, then, that there weren`t previous industrial civilizations on Earth that rose and fell long before human beings appeared?