alternatehistory.com

The latest re-evaluation of the Younger Dryas Event seems to make the "comet" hypothesis unlikely, but the idea that the earth experienced a "super-Tunguska" event between 12,900-10,000 BC could apparently have occurred without altering earth's ecology too much--but for the purposes of this scenario, with one major exception.

We'll assume the comet struck relatively late in history--close to the 10,000 BC mark, after the last probable ancestors of the Native Americans had already made it the continent. The impact, probably equivalent to thousands of megatons, wipes out not only the American megafauna, but the human population as well. Man never manages to reach South America. The last of the Native groups, the ancestors of the people who would in OTL become the Eskimo/Inuit, arrive two thousand years after the cataclysm, but fail to thrive on the devastated continent.

Now we'll assume that history somehow unfolds normally in the Old World, giving rise to familiar cultures and events. 11,000 years after the extinction of the first wave of humans in the Americas, the Vikings reach the shores of northeastern Canada...how do you see history proceeding from there?
Top