Between 12,800 years ago, and 11,600 years ago, the ice age ended, Hard. There's a lot of theories on what caused it, (probably a comet impact on the Canadian ice sheet) but evidence is becoming more clear all the time that it was a cataclysmic time across most of Earth. There was a mass extinction, sea levels rose 400 feet, and we are now left with only legends of great civilizations that sank under the sea.

The more we learn about this time, the more we find out that we are a Species With Amnesia.