B) What they're looking for is not on land, but in water up to 100M deep. Only the very last of the "red paint" people would have moved that far inland as the climate warmed, and the seas rose up to their modern levels.
Good point, but that close to the Laurentide ice sheet would have seen some rising after it melted.
Although modern scholars no longer believe in the diffusion theory it was once thought that the Red Paint people traveled across the Northern Hemisphere from Europe to North America.
The diffusion theory was based on similarities between the Red Paint people's stone tool technology, houses, and ritualistic burial habits that included the use of red ocher. Red ocher is common in many geographic regions, and is commonly used in many prehistoric cultures. The stone technology and similar geometric designs of dots and lines that appear on the stone tools of both the North American Red Paint culture and on the tools of European prehistoric cultures could have developed independently of each other.
As scientific methods improved, over the years, it has been determined from studying the burials and skeletons of the Red Paint people that they are in fact Native Americans.