According to the internet, the human race has been in existence for roughly 200,000 years. Aside from the fact that we've never found one, is there any reason why a civilization couldn't have existed 20 - 150,000 years ago? Also, is it possible that geographical changes might have left evidence of truly ancient civilizations buried, sunk or otherwise obscured in ways we haven't considered, or have the capacity to explore?
Perhaps you would be interested in this answer I gave in a previous topic. In summary, the climate was not stable enough to allow for people to adopt widespread agricultural practices which aid in creating large populations. It is unlikely there is a "lost civilization" lurking somewhere in the soil that dates before 12,000 years ago.