A question I'm often asked is: Why don’t we find any fossils of humans in the layers of sediments with dinosaurs? If dinosaurs and people lived together, why do we find dinosaur fossils but no humans, supposedly not even the remnants of their civilizations?
This is a totally valid question, and there actually are no easy answers to it.
Various creationists have postulated several scenarios, which might be valid, or partly valid, or not valid at all. I'm not really comfortable with any that I've read so far. So, here are several possibilities that I personally would suggest:
1 - Mathematically, there could have been several billion people on the earth at the time the flood started. However, since the Bible describes humans as being only evil continually, it could possibly be that the human population on the planet had been drastically decimated by crime, wars, murder, disease, etc.
It is possible, then, that the human population might not have been that great at the time of the flood. Hence, there might not have been huge numbers of humans around when the
flood started.