[Drammach]

(Going from memory) Current estimates on existance of "modern man" go back approx. 50,000 years..

Judging from that, given a means of travel to the North American continent, inhabitence by early human is possible..

Next question is, why isn't there more evidence of their existence ?
If conditions were good, ( hunting, etc..) then such a population, even a small one, would have thrived and grown..
Thus, there should be ample evidence of pre-glacial habitation..

I'll have to take this one with a grain of salt..
Possible, but not likely..

[SunkenCiv]

I'll ping blam as well, I'm sure he has a number of topic links to post regarding your question.

Briefly, the idea that the spread of modern humans across the Earth began about 50,000 years ago is part of the Replacement model, which I don't accept anyway.

The other problem -- that there isn't more evidence -- is easy to explain. There is and has been plenty of evidence, but it was rejected on a priori grounds under the "Clovis First and Only" bias (I call it a bias because it was never a scientific theory). Here's a quickie about the Calico site (not cats) as an example. Tom Dillehay suffered ad hominem attacks for 20 years over his findings at Monte Verde, which are now accepted as the consensus. Ironically, I think the NAGPRA will lead to many such findings, pushing back human antiquity in the Americas.

Hope this helps.