When Did Humans Reach the Americas?

This question has been simmering in the back of my mind for decades. I’ve given panels on it at science fiction conventions, and I’ve written blogs on the subject before, too. I believe the last blog I wrote about it theorized that an ice-free channel through the North American glaciers of the last ice age opened up about 14,000 years ago. And therefore people who had crossed the Bering landbridge sometime before that were finally able to leave Alaska and find their way south to the plains of central North America. And from there, they could have gone on to populate all the rest of North America, Central America and South America.

But even that might not be right.

The other night, we watched a documentary about fossilized footprints in the White Sands National Park in New Mexico. Although the area is a desert now, during the last ice age, it housed a large lake. The fossilized footprints recorded the presence of Columbian mammoths, great ground sloths, North American camels and horses. And among all those footprints, it is not at all unusual to find lots of human footprints.

Scientists have to work fast to learn all they can from these footprints, because as soon as they are revealed by the wind blowing the sand away, the blowing sand starts to erode the footprints away. For these are not the usual fossils that have been turned into stone. Some of the footprints are impressions in the sand, that had been filled with silt that was finer than the sand around them. Others are outlined with bulging sand indicating the weight of the animal. All of them dried out when the lake dried up, and little has happened to the area to disturb them. Except the blowing wind.

A number of scientists work the site each year, and I was left with the impression that each year presents a new batch of footprints, at a slightly lower level than the year before.

One year—and it didn’t say what year it was—a pair of scientists who are experts at radio-carbon dating dug a trench in the sand, going down through several layers of human footprints. But you can’t radio-carbon date sand; you can only radio-carbon date organic material, like plants or animals. By examining the layers between the human footprints, they were able to find organic material, such as seeds or pollen. They packaged up a number of these samples and took them back to their lab in Denver to date them.

Two years later, the narrator visited them in their lab to ask what kind of dates they had gotten from their samples. They said they had gotten dates between 21,000 and 23,000 years ago! That would have been long before the ice-free trail through the glaciers had opened up!

At the very end of the show, the narrator was talking to another scientist, and wondered how humans could have gotten so far south before the glaciers had started to melt. The anthropologist said they had probably followed the Pacific coastline, starting in Alaska and working their way south. But, he pointed out, the sea level was much lower at that time (as much as 400 feet lower), with so much water tied up in the glaciers, so any settlements they might have established would be underwater now. He suggested we should be doing more diving along the coastline to find them.

Okay. Who still thinks that ancient alien visitors brought a herd of humans to the Americas? (This was the last suggestion I made when I gave this talk at conventions.)