The Glacial maximum was 25,000 years ago. For some reason they want
there to be an open corridor on land between ice covered landscapes.
Inuits have made it across ice sheets to Greenland. You probably have
to be able to kill enough seals or fish on the sea ice to survive the
crossing, but my guess is that humans could have crossed any time during
the last glacial period. It would not have been easy, but humans can
obviously do it. The warm and cold periods have been about the same for
the last 5 ice ages, and the ice ages have been on their 100,000 year
cycle for the last million years.
> Here's a link to the abstract of the cited paper:
> Here, we present evidence from excavated surfaces in White Sands
> National Park (New Mexico, United States), where multiple in situ
> human footprints are stratigraphically constrained and bracketed by
> seed layers that yield calibrated radiocarbon ages between ~23 and 21
> thousand years ago. These findings confirm the presence of humans in
> North America during the Last Glacial Maximum, adding evidence to the
> antiquity of human colonization of the Americas and providing a
> temporal range extension for the coexistence of early inhabitants and
> Pleistocene megafauna.
> This date is thousands of years earlier than the dates suggested by
> Clovis stone tools of about 12K years BP, and closer to even eariler
> dates of at least 32K years BP of Pedra Furada sites in Brazil.
> The region is a high basin completely surrounded by the San Andres and
> Sacremento Mountains deep in the American Southwest. Although the
> past climate almost certainly was wetter and milder than the present,
> I can only imagine what would motivate someone to walk hundreds of
> miles to go there.
Like I indicated above the sea levels have dropped and the ice sheets
have extended to about the same extent for the last 5 ice ages (over
half a million years). Humans likely had to only wait until the
technology was developed to allow them to make the crossing. If we can
get ancient DNA what we might find is that if there were humans here in
the Americas 32,000 years ago that they didn't make it. Small bands may
have made it over, but they may have never estabilished successful
populations. Inbreeding depression and the changing environment (the
glacial max wouldn't occur until 25,000 years ago) could have done them
in before more successful migration events occurred.
Unless they were living on the sea ice there likely were no humans
living around Tierra del Fuego during the glacial max 25,000 years ago
because it was one big ice sheet.