The standard model, in my understanding, is that people crossed Beringia during the most-recent Ice Age, at which time the sea-level was decreased let's say 15 thousand years before present (BP,) and that the emergence of organized material hunter-gatherer culture in about 11,500 BP, amongst the so-called Clovis people, supports this hypothesis.
And it's true, mostly but it's incomplete.
There is evidence from archaeology (both via radiocarbon dating and skeletal-morphology analysis) and from genetics (the study of the minority mitochondrial DNA constituent "haplogroup X") that do not let this accepted version of ancient immigration rest easily.
Across the Americas, there are several archaeological sites of apparent conspicuous antiquity far from the Clovis region and possibly of even profound antiquity.
One of the first great challenges to the Ice-Age-Beringian-crossing theory came from the 1975 discovery of the remains of a human encampment in Monte Verde, Chile. The radiocarbon-derived dating of ca. 14,800 years BP is now not controversial. A deeper layer *is* controversial but we don't even need to get into that right now. (The fella who acquired the accepted dates for the upper layer "remains cautious" about speculation of a proposed 33kBP dating for the lower one.)
|Theories about early human migration to the Americas were originally and quite logically based only upon the "Bering Strait" theory....|
There are others. In 2004, an archaeologist claimed he'd found charcoal evidence of humans at the Topper dig in South Carolina dating from 50,000 BP. It remains controversial. Evidence not proof....
Cactus Hill in Virginia appears to provide stone tools from 15 to 17k BP.
Meadowcroft Rockshelter in Pennsylvania, 16 to 19k BP.
Anyhow. The point is clear enough there seems to be emerging plenty of evidence of sites of conspicuous antiquity, an antiquity that is troubling for the Beringia-first, Clovis-culture-centric hypothesis. The suggestion that some of this evidence is profoundly ancient is only further intriguing; but never mind that I'm only trying to support the idea that the standard model is incomplete.
Then there's the skeletal evidence. There appears to be quite a bit of it, more appearing all the time.
Kennewick Man is notable but not for his antiquity. He's "only" ca. 9k years old; but he shares a characteristic with "Penon Woman III," who may be related to the Pericues of the Baja Peninsula, a peculiar variety of people who died off after the arrival of Europeans. All of these are notable for their morphology, which is not consistent with that of the Amerindians.
Penon Woman was one of 26 skeletons discovered in 1959 near the shore of the erstwhile lake at the site of the present Mexico City. She appears to have lived about 12,700 years ago.
Luzia, discovered in Brazil in 1975, is the skeleton of a woman who dates from about 11,500 BP. She too had a morphology disimilar to Amerindians.
These discoveries provide a serious challenge to the idea that migration to the Americas happened only during the brief decrease in sea level that allowed hunters to cross from Siberia. Their age is not profoundly great but they're skeletons really good evidence, from long ago, and far away from Alaska.
Okay. So that addresses the radiocarbon dating and the skeletal morphology. One more thing the mitochondrial DNA.
Xenia. Haplogroup X (and here I'm only parroting information that I do not hope to ever understand. I'm simply paraphrasing that which I believe is a matter of accepted academic record.)
Haplogroup X, which may have originated amongst the Druze minority population in the Levant and is prevalent across the Middle-East and less so in Europe, has a small but conspicuous presence amongst pre-Columbian North Americans. About 3% but more in the Northeast. Amongst the Algonquins, 25% (according to Wikipedia.) It's 5% amongst the Yakama....
The four other (and more-prevalent) mitochondrial DNA variations within the pre-Columbian American population clearly associate with Asia, as do the only two branches of Y-DNA. Haplogroup Xenia does not seem to have arrived from that direction.
The standard theory about the peopling of the Americas is under suspicion.