I think we've almost been wiped out at least once before, http://www.npr.org/sections/krulwich/2012/10/22/163397584/how-human-beings-almost-vanished-from-earth-

I think we've almost been wiped out at least once before, http://www.npr.org/sections/krulwich/2012/10/22/163397584/how-human-beings-almost-vanished-from-earth-in-70-000-b-c http://www.npr.org/sections/krulwich/2012/10/22/163397584/ho...