Not quite eternity, but ... When I was in grade 7 or 8, our geography teacher one afternoon drew a line with a piece of chalk, starting at one end of a black board, going the full length of that black board, which was the length of one wall, then continued on to the blackboard on the next wall, and went almost the full length of that black board, stopping just a few inches from the end. "If that line represents the age of the universe", he said, "then the length of time man has existed is this little bit of chalk at the very end of that line."

That made quite an impression on me.