Its an expression that say that something happened, but it can't possibly be from time itself, something else to to be involved. Example: If someone says, "Mount Rushmore was created from weather." Someone might say, "The sheer passage of time does not account for it." This would mean that just time or all these years did not make Mount Rushmore happen, someone or something else had tohave a hand in creating it.

It means pure or unmixed. The passage of time by itself does not account for it.