I love this topic and ponder it often. There have been three mass extinctions in earth's history resulting the dominant species on earth being wiped out which carved the way for the next era of dominant species to begin. A few other apocalyptic realities include the possibility of a gamma ray burst from a supernova explosion of a dying star headed in our direction, and the inevitable death of our sun and its expansion into a red dwarf which would envelop the earth. That last one in an unavoidable eventuality. Fortunately we have approximately 5 billion year for that to occur. It certainly would behoove our generation or one of the next few generations to get populations of humans on other planets or installations to assure the preservation of humankind. Great post and following you.