Dryer I can ask Dr Ot about that question but my understanding of her statement is that there were no humans on North America at that time and that ALL humans everywhere on the planet died except for a handful in southern Africa. That we are ALL descendant from 40 to 100 females that survived.

There has been a lot of work on the bacteria from space thing. They did find bacteria on the moon and they have found fossil bacteria in meteorites. A lot of this work has been done since 2000 and many university microbiology web site can offer more detail under extremophile prokaryotes. But its not my job to convince you... thanks
Jim
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These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.