Homo sapiens mostly didn't leave Africa until about 100k years ago, but when dealing with these things there is always a fair amount of uncertainty so some could have left much earlier.

There are also other early human species besides Homo sapiens that could in theory be responsible for something like this.

Homo erectus was galavanting around the world perhaps up to 2 million years ago, and they were tool users. Homo heidelbergensis was on the move around 600k years ago. Homo neanderthalensis was out of Africa around 300k years ago.

maybe there was a form of homo erectus already in america, using stone tools etc, having arrived 130k yrs or more ago, and then the indians wiped them out when they arrived much later--that would explain indian tales of having wiped out primitive cannibal tribes (a movie called bone tomahawk was inspired by these tales)...of course the political considerations would tend to suppress this idea.

Come on, you can't take legends from circa 1500 AD to be evidence of anything that happened somewhere between 11,000 and 20,000 years earlier, especially without writing. It's far more likely that primitive cannibal tribes were made up wholesale than that societies carried the memory of them for more than 10,000 years.

The Klamath Native American tribe has legends of the eruption of Mt. Mazama that formed Oregon's Crater Lake - which happened in ~5677 BC [1]. If oral legends that reflect real events can last seven and a half thousand years, is there any reason to think they couldn't last 15ky, or 20ky? It seems to me all that's needed is a continuous cultural line.

[1] https://en.wikipedia.org/wiki/Llao

Well, it wouldn't be entirely unprecedented.

See: "Indigenous Australian storytelling accurately records sea level rises 7,000 years ago"

https://www.theguardian.com/australia-news/2015/sep/16/indig...

There is a competing hypothesis of Recent African origin that states humans evolved over 2 millions years in Eurasia and Africa.

> Multiregional evolution holds that the human species first arose around two million years ago and subsequent human evolution has been within a single, continuous human species

https://en.wikipedia.org/wiki/Multiregional_origin_of_modern...

https://upload.wikimedia.org/wikipedia/commons/c/ca/Homo-Sta...

The suggested date for this puts it the other side of a genetic bottleneck [1]. Whatever was the cause for this, there is evidence that human population numbers reduced at some point.

[1] https://en.wikipedia.org/wiki/Toba_catastrophe_theory

Paleontology is built up out of the most tenuous of evidence. Whole pages of children's dinosaur books are extrapolated out from one or two fragmentary skeletons of unfortunate creatures that just happened to die in places where their corpses were covered up by preserving sediments, instead of being picked apart by scavengers.

Archaeology is a little better, just because it's more recent, and there's more stuff that has managed to survive, but in the absence of ceramics, metals, or large-scale use of stone, almost everything that primitive humans would use is extremely perishable, with the exceptions being where we just happen to have found bodies and graves in extremely preservative conditions, like bog people, or the Peruvian desert cave mummies, or frozen in glaciers. I've an uncle who is an archaeologist specializing in post-contact Native American sites, and the vast majority of the time, the only identifying aspects of a site will be that he's stumbled onto an ancient trash heap, full of discarded and broken mollusk shells.

There is always a first discovery. Arguing that it can't be true because it it were, it would have been found earlier is therefore not logical.