I guess my blimp joke went over like a lead- uh, forget it. ;')
My view is that humans have been in the Americas for a very long time, and remains will be found pretty much as deep as anyone cares to keep digging. Problem is, the preservation of remains is rare, as shown by the vanishing of much more recent remains, like, say, my great-great-grandmother.
If I had to guess, I'd say the Barringer impact ("Meteor Crater") had negative consequences on North American inhabitants (and animal species) over a wide area, perhaps opening the door a bit for a more recent wave, or more than one. Also, glaciation dropped global sealevel, meaning that plenty of potential sites are now part of the continental shelf and submerged.
More to the point, the water's edge was lower altitude, and all other things being equal, the lower the altitude, the warmer the climate. Getting to the Americas from Europe or eastern Asia (or vice versa) by boat was probably commonplace, and probably happened more than once.
:')
Well, you know how it is; you gotta draw a picture for we Nenaderthals ;^)
And yeah, it sounds like a needle in a haystack sorta thing, which I suppose explains so many "accidental" finds.
Do you know right off hand what length the average glacial cycles runs. Seems like ~20,000 years??? In any event, I would expect much of ancient civilizations would be near a coast AND fresh water both. And there would be some movement inland by a few "explorers", again staying near fresh water sources over hundreds maybe thousands of years. So yeah, it would seem there is probably a trove of artifacts....under water.....near river mouths?
great-great grandmother, eh?
FGS
LOL. I was ridiculed here four years ago when I ask the question, "I wonder how many humans were killed from the Barringer Impact?"
A less 'crazy' question these days, it seems.
"The classic "ancient site" in the New World is "Calico," located in the Central Mojave Desert of California (Shlemon and Budinger, 1990). Two issues have dogged acceptance of Calico by mainstream archaeologists: (1) the authenticity of the artifacts; are they truly the product of human manufacture, or merely naturally produced "geofacts?" and (2) the obvious pre-Clovis age of the deposits (see, for example, lengthy discussions in Leakey and others, 1968; Haynes, 1973; Bryan, 1978; Taylor and Payen, 1975; Carter, 1980; Meighen, 1983; Patterson, 1983; and Budinger and Simpson, 1985).
A lot of these old 'artifacts' became known as "Cartifacts" because George Carter found so many of them.
Carter was a geologist and could not get anyone to take his discoveries serious...so, he obtained a PhD in archaeology...with the same result, lol.
Carter wrote a good book years ago titled: Older Than You Think.