The most recent glacial period started 120,000 years ago and ended about 12,000 years ago. During the glacial period, much of the earth would have been covered

The most recent glacial period started 120,000 years ago and ended about 12,000 years ago. During the glacial period, much of the earth would have been covered with ice and the agriculturally habitable band around the equator was much smaller. Nomadic hunter gatherers, on the other hand, would be able to move around and follow the fauna that had adapted and survived. This is roughly around the time that humans started wearing clothing (based on body lice molecular clock studies) so hunter gatherers would be able to occupy much larger areas with a much larger diversity of food sources than any agricultural society tied to its productive land. IIRC one of our genetic bottlenecks is from this time period so humanity barely survived as it is and the glaciers would have destroyed most evidence of human habitation, especially when it's in an open field ala agriculture. The stuff that survives was generally buried in a cave of some sort and protected from the elements so even if they had discovered agriculture, evidence of that fact would not have survived. During the glacial period the sea level was also much lower than it is now, so all the settlements are now far underwater, if they existed at all.