Ecclesiastes 3

"For what happens to the sons of men also happens to animals; one thing befalls them: as one dies, so dies the other. Surely, they all have one breath; man has no advantage over animals, for all is vanity.  All go to one place: all are from the dust, and all return to dust. Who knows the spirit of the sons of men, which goes upward, and the spirit of the animal, which goes down to the earth?" vv.19-21

Read chapter 3
Dust.  It's what we were and what we will be.  Just as it says in Genesis 3:19, "In the sweat of your face you shall eat bread till you return to the ground, for out of it you were taken; for dust you are, and to dust you shall return.”  This goes for believers and nonbelievers alike, the difference will be in the resurrection.  Here it compares men and animals that all have the same ruach (Hebrew for spirit or breath).  Just because man has dominion over animals doesn't mean man has dominion over what happens at death.  Now this isn't saying that dust is "hell" or heaven.  It's saying we become earth again and our spirit or break departs from us.  Just as the beginning of the chapter says "there's a time to be born and a time to die" (v.2) so we all are appoint once to die: "And as it is appointed for men to die once, but after this the judgment," Hebrews 9:27.  He asks the question "who knows if the spirit of man rises?" Do you?  If so prove it.  
Is it hard to admit we are but dust?  Yet praise the Lord, He has made beautiful things out of dust!