An interesting piece of research from Spain – see http://phys.org/print296738850.html … the facts on the ground don't appear to fit the assumed picture. Mountain glaciers reached a maximum at 26,000 years ago (in Iberia) but the maximum spread of the northern ice sheet occurred at 20,000 years ago – a 6,000 year difference. Why is this?
So, what was happening – was the maximum extent of the ice sheet really at 20,000 years ago or has ice sheet extent been compromised and not all that evidence is due to ice. Might water better explain some of the erratics and gravels, etc.
The mountain glaciers were measured not just by rocks but by using stalagmites and stalactites found in caves in the mountains. These are formed by water dripping through the rocks and are thought to reflect precipitation levels. In other words, it was wetter at 26,000 years ago than it was at 20,000 years ago. This is basically the conclusion. The authors of the paper point to the presence of huge lakes in what is now Utah and Nevada (the Great Basin) at around the same time, saying they were in existence for around 6,000 years. Are they restricted to such a short life time?
The discrepancy in date could also arise as a result of a different dating technique (as outlined in the paper). Whatever, there is a problem.