This song has generally a dirge-like tone, envisioning a bleak future for the human race, sounding much like something out of 'Brave New World', for example. The lines cited above begin the last verse, immediately following a penultimate verse that begun with "In the year 9595". So if that year completed the ten thousand years referred to in these lines, that ten millennium period would have started with 5 BC. This song came out in 1969, when referring to the entire human race as "Man" had seldom if ever been objected to. So that time frame and reference must mean that from 5 BC through 9595 AD, "Man" (i.e. the human race) had cried a billion tears. From the song's overall bleak tone, these lines must be meant to refer to much anguish and misery, right? But what would a billion tears in 10,000 years actually mean? That would mean an average of 100,000 tears per year during that time. If the human population remains in the the billions or even in the millions through 9595, that's way less than one tear per person per year! Maybe the human population will drastically drop in the future, even though so far it has steadily been rising since 1969. And since the ten thousand years referred to herein seem to begin back around the birth of Jesus, the human race had already cried vastly more than a billion tears from then until the song's release in 1969. So, many tears would have to be somehow uncried from 1969 to 9595 to make the lines accurate. But even if the billion tears were envisioned to be those cried between 1969 and 9595, the world would be way way over that billion even by now in the early 21st Century. Any way you look at it, a human race crying ONLY a billion tears in the better part of 10,000 years would mean only a trivial amount of crying. That would be consistent with a quite bright future, NOT the bleak future of this song's overall tone!