Because we have so many written records…..
In reading Graham Hancock’s America Before I learned that the Younger Dyas event consisted of 21 years of bollides crashing to the planet twice a year—in June and again in late October, early November. The intensity was the greatest for the first 14 years and began tapering the last seven years. Unbelieveable that any humans lived through that—of course North American was wiped clean-—and this was before the event that brought an end to the Ice Age itself...