Are these time lines credible? I always thought the people of Asia could have come as late as 2000 BC over the land bridge and then massed into 50 million or so by the time Cortez arrived. Does the 12,000 year time table preclude the land bridge theory?
One early view about antiquity of humans in the Americas was about 1000 BC, with some of the (still) puzzling monumental construction attributed to a poorly-understood and poorly-articulated collection of "Old World" civs, such as the Phoenicians. The Viking presence before Columbus is now of course documented in archaeology, but their numbers were apparently too small to move the needle when looking at what passes for Native American DNA; either they didn't intermarry, which is likely, and eventually returned to Europe, or whatever genetic heritage they left vanished through luck of the draw and give or take the vanishing of entire tribes post-Great Migration (that's the relevant geographic area).
During the 1920s (if memory serves) the antiquity got a major bump backwards into time with the discovery of stone-age technology families, the oldest (then) known being Clovis (named for the place of first discovery). This was widely doubted, and not accepted until the 1950s after the radiocarbon method was discovered and verified (and somewhat increased) the age of the Clovis period.
Hidebound as the academic community is (always and everywhere), the higher date rotted into what I call Clovis-First-and-Only, a rubbish idea that humans knew nothing about boats, a weird claim to make considering the maritime hunting and fishing that goes on to this day on both sides of the Bering Strait. Also, the dates on sites like Cactus Hill and Dillehay's site in South America don't fit the CFAO narrative.